Kaiser Aluminum Electrical Bus Conductors Technical Manual

!,.,~ i ".'. 'i! 'i KAISER ALUMINUM ELECTRICAL BUS CONDUCTORS TECHNICAL MANUAL } '.I ,::,,,';' KAISER ALUMINUM ...

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KAISER ALUMINUM ELECTRICAL BUS CONDUCTORS TECHNICAL MANUAL

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KAISER ALUMINUM ELECTRICAL BUS CONDUCTORS TECHNICAL MANUAL

FIRST EDITION

KAISER ALUMINUM & CHEMICAL SALES, INC. 919 North Michigan Avenue Chicago 11, Illinois

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EDITORIAL ACKNOWLEDGEMENT Information presented in this book was compiled and written by Chester G. Sorflaten, Electrical Condnctor Sales, Kaiser Alnminum & Chemical Sales, Inc., as a company service to the Electrical Indnstry. Factual data have been obtained from numerous individuals and companies whose help and cooperation Kaiser Aluminuul gratefully recognize. In addition, acknowledgement is offered to the othel' personnel throughout this company and the complete staff of the Technical Publications Department whose combined efforts have made this book possible.

J. M.

AnLE,

Technical Editor

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Copyright 1957

by Kaiser Aluminum & Chemical Sales, Inc.

TABLE OF CONTENTS Page

Page

SECTION I: General.

1-13

Dt . . 0 f~ R' e ermmation

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27

dc

ALLOY CHARACTERISTICS AND PROPERTIES. .. Physical Properties : . . . . .. Electrical Properties . . , , .. Conductivity . . . . . . . . . . . . . . . . . .. Resistivity Thermal Properties of Aluminum Bus Conductors. . . .. Temperature Coefficient of Resistance. . . . . . . . . . .. , . . . . . . . . . . . . . . . . . .. Specific Heat ,............. Thermal Conductivity Effect of Heating on Tensile Strength. . . . . . . . . . . .. '" ,. '" . Creep Conosion Resistance General Classes of Bus Conductor Alloys. . . . . . . . . . .. Non-Heat-Treatable Bus Alloys .. ,. ... . .. . .... .. Temper Designation for Non-Heat-Treatable Bus Bar Alloys. . . . . . . . . . . . . . . . . . . . . . . . . .. Heat-Treatable Bus Alloys. . . . . . . . . . . . . . . . . . . .. Temper Designations for Heat-Treatable Bus Bar Alloys. . . . . . . . . . . . . . . . . . . . . . . . . ..

1 1 2 2 2 2 2 3 3 4 5 5 6 6 6 6

Problem No.2. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 27 INDUCTIVE REACTANCE OF BUS CONDUCTORS. Solid Round and Round Tubular Bus Conductors. . . .. Inductive Reactance to a One-foot Radius. . . . . . . .. " Inductive Reactance Spacing Factor Geometric Mean Distance (GMD). . . . . . . . . . . . .. Inductive Reactance of Rectangular Bars. . . . . . . . . .. Graphical Solution Using Reactance Curves. . . . . .. Methods of Calculation. . . . . . . . . . . . . . . . . . . . . . .. Widely Spaced Conductors. . . . . . . . . . . . . . . . . . . .. Inductive Reactance of Square Tubular Conductors and Channels in Box Form. . . . . . . . . . . . . . . . . .. Method of Calculation. . . . . . . . . . . . . . . . . . . . . . . .. Graphical Solution Using Reactance Curves ..... " Problem No.3. . . . . . . . . . . . . . . . . . . . . . . . . . . . . ..

8 8 8 9 9 9 9 10 10 10 10 11 11 11 11 12 12 12 12

MANUFACTURING PROCESS AND TOLERANCES .. Extruded Bar and Shapes. . . . . . . . . . . . . . . . . . . . . . . .. Tolerances . . . . . . . . . . . . . . . . . . . . . . . . . .. Rolled Bar and Structural Shapes. . . . . . . . . . . . . . . . ..

12 13 13 13

35 35 35 38

BUS IMPEDANCE : Problem No.4 Voltage Drop-Vectorial Relationship. . . . . . . . . . . . .. '" , Problem No.5

39 39 39 40

CURRENT RATING OF BUS CONDUCTORS Current Rating of Round Conductors. . . . . . . . . . . . .. Heat Loss by Convection-Outdoor Rating Heat Loss by Convection-Indoor Rating. . . . . . . .. Heat Loss by Radiation. . . . . . . . . . . . . . . . . . . . . . .. Method of Calculation. . . . . . . . . . . . . . . . . . . . . . . .. Limitations of Round Conductors-Solid and Tubular Cunent Rating of Rectangular Bar. . . . . . . . . . . . . . . .. Effect of Width of Bar on its Cunent Rating. . . . . .. Effect of Bar Thickness on Current Rating. . . . . . . .. , Effect of Position on Cunent Rating Cunent Ratings of Multiple Bar Arrangements. . . . . .. Current Rating for Square Tubular Bus. . . . . . . . . . . .. Current Rating for Standard Channels and Angles. . .. Cunent Rating for Non-Standard Bus Shapes Conversion Factors .Effect of Bus Enclosures. . . . . . . . . . . . . . . . . . . . . . . .. Effect of Painting Bus Bars. . . . . . . . . . . . . . . . . . . . . ..

40 41 41 41 42 42 43 43 43 44 44 46 46 46 46 46 48 49

SECTION III: Mechanical Design SECTION II: Electrical Design

29 29 29 30 30 30 30 34 35

7

BUS CONDUCTOR SHAPES " Rectangular Bar . . . . . . . . . . . . . . . . . . . . . . . . . .. Edge Contours Alumimun Rectangular Bar Alloys. . . . . . . . . . . . . .. Alloy Selection . . . . . . .. Bending Properties . . . . . . . . . . . . . . . . . . . . . . . . . .. Specifications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. Round Tubular Conductor. . . . . . . . . . . . . . . . . . . . . .. Electrical Characteristics . . . . . . . . . . . . . . . . . . . . .. Alloys Bending Properties " Square Tubular Conductor. . . . . . . . . . . . . . . . . . . . . .. Electrical Characteristics . . . . . . . . . . . . . . . . . . . . .. Alloys : . . . . . . . . . . . . . . . . . . . . . . .. Channel and Angle Conductor. . . . . . . . . . . . . . . . . . .. Applications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. Alloys Fabrication Other Conductor Shapes. . . . . . . . . . . . . . . . . . . . . . . ..

15-49

D-C RESISTANCE OF BUS CONDUCTORS Calculation of D-C Resistance. . . . . . . . . . . . . . . . . . .. Problem No.!. " Temperature Conversion of D-C Resistance " Temperature Coefficient of Resistance (it)

15 16 16 16 17

A-C RESISTANCE OF BUS CONDUCTORS Skin Effect . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. Effect of Bus Shape and Size on A-C Resistance. . . . .. Rectangular Bars Tubular Conductors . . . . . . . . . . . . . . . . .. . . . . . . .. Channels and Angles Arranged in Box Form. . . . . .. Calculation of A-C Resistance Independent Variable . . . . . . . . . . . . . . . . . . . . . . . .. Shape Parameter . . . . . . . . . . . . . . . . . . . . . . . . . . . ..

18 20 20 20 21 23 23 23 27

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51-72

SHORT CIRCUIT FORCES oN BUS CONDUCTORS. Lateral Forces , Value of k Short Circuit Cunent. . . . . . . . . . . . . . . . . . . . . . . .. Symmetrical Currents . . . . . . . . . . . . . . . . . . . . . . . .. Asymmetrical Currents . . . . . . . . . . . . . . . . . . . . . . .. '. . . . . . . . .. Effective Current NEMA Standards . . . . . . . . .. Calculation of Fault Current. . . . . . . . . . . . . . . . . . . . .. Calculation of Lateral Short Circuit Forces , Force between Two Conductors. . . . . . . . . . . . . . . .. Force on End Conductor of Three-Phase Bus Spaced Horizontally . . . . . . . . . . . . . . . . . . . . . . .. Force on Center Conductor of a Three-Phase , Bus with Flat Symmetrical Arrangement Forceon Each Conductor in a Multiple Bar Arrangement

51 51 52 52 52 52 54 54 55 56 56 56 56 58

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Vibration and Resonance , Stress Factors Longitudinal Forces Torsional Forces . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ..

59 59 60 61

BUS DESIGN . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. Clearances " Deflections of Bus Conductors Bare and Loaded " Bus Loading-Ice and Wind Ice Loading . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. Wind Loads . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. " Combined Ice and Wind Load Formulas for Deflection and Stress of Bus Conductors. Calculation of Deflection and Stress in a Typical Bus Installation " Expansion of Aluminum Bus Conductors " Calculation of Bus Expansion. . . . . . . . . . . . . . . . . .. Types of Expansion Joints. . . . . . . . . . . . . . . . . . . . .. Application of Expansion Joints " Methods of Support for Buses. . . . . . . . . . . . . . . . . . . .. Fixed Supports in Center Only " Fixed Supports at One End Only " Fixed Supports at Both Ends. . . . . . . . . . . . . . . . . .. Fixed Supports at Intermediate Points " Fixed Supports at!Center and Both Ends. . . . . . . . ..

61 61 62 63 63 63 65 65

SECTION IV: Joining Bus Conductors

69 70 70 71 72 72 72 72 72 72 72

73-103

PREPARING ALUMINUM CONTACT SURFACES Aluminum to Copper Joints , , . .. Silver Plated Contact Surfaces Other Methods of Surface Preparations

73 74 74 74

JOINT RESISTANCE Total Joint Resistance. . . . . . . . . . . . . . . . . . . . . . . . . .. Contact Resistance for a Uniformly Applied Pressure . . . . . . . . . . . . . . . . .. Metal Resistance in a Lapped Joint with Uniformly Applied Pressure Joint Resistance of Bolted Bus Bars , Effect of Overlap on Bolted Bus Bars. . . . . . . . . . ..

75 75 75 76 77 77

77 77 , 78

JOINT BOLTING PRESSURE Distribution of Applied Force in a Bolted Joint Bolting Methods

JOINT DESIGN , . . . . . . . . . . . . . . . . . . . . . . .. Heating in a Typical Bus Joint. Effect of Heating in a Bus Joint. Current Limitation per Bolt , '" , Design of a Lapped Joint" Multiple Bars per Phase , ,, Joint with Silver Plated Surfaces "

79 79 79 80 80 80 81

CLAMPING FORCES DEVELOPED BY BOLTS ..... Joint Stresses Developed by Bolted Clamping Forces.. Reducing Joint Stresses with Flat Washers ,. Strength Characteristics of Fasteners , . .. Aluminum Bolts Steel Bolts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ..

81 81 83 83 83 84

BELLEVILLE SPRING WASHERS. . . . . . . . . . . . . . .. Belleville Washer Design , , . . . .. Belleville Spring Materials and Finish Selection of a Belleville Washer , "

85 85 86 86

WELDING ALUMINUM BUS BAR Melting Point and Thermal Capacity .. ,

87 , .. 87

Page

Thermal Conductivity 87 Oxide Films , 88 Porosity 88 Thermal Expansion and Contraction. . . . . . . . . . . . . .. 88 Effects of Welding Heat on Bus Bar Properties. . . . . .. 88 Preparing Aluminum Bus Bar for Welding ..... " ... 89 Joint Design and Edge Preparation. . . . . . . . . . . . .. 89 Cleaning of Welding Surfaces , '" ., .. " 89 Preheat ' , . .90 Choice of Welding Method 90 Welding Methods for Aluminum Bus Bar. . . . . . . . . .. 90 Gas Welding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 90 Equipment for Gas Welding 90 90 Gas Flame Adjustment , Filler Rods , .. ,................. 91 Welding Flux , , .. , 91 Edge Preparation ahd Cleaning before Welding 91 Preheating . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 93 Welding Procedure 93 Cleaning after Gas We1ding. . . . . . . . . . . . . . . . . . .. 93 Physical Properties of Gas Welded Work Hardened Alloys (EC & 1100) . . . . . . . . .. . . . . .. 93 Properties of Gas Welded, Heat-Treatable Alloys (6101, 6061, & 6063) , . . . . . . . . . . . . . . . .. 93 Metallic Arc Welding , '" . " .. 94 Equipment 94 Electrodes 94 Edge Preparation and Cleaning Before Welding 94 Preheating and Welding Procedure 95 Cleaning after Metallic Arc Welding. . . . . . . . . . . .. 96 Properties of Metal Arc Welds , .. ; . . .. 96 Tungsten-Inert-Gas Welding (TIG) 96 Equipment 96 Filler Rods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 96 Gas Coverage 96 Edge Preparation and Cleaning before Welding , 96 Preheating and Welding Procedures. . . . . . . . . . . .. 98 Properties of TIG Welded Bus , '" 98 Metal-Inert-Gas Welding (MIG) 98 Equipment 98 Filler Wire , , 99 Gas Coverage 99 Edge Preparation and Cleaning before Welding. . .. 99 Preheating and Welding Procedures 100 Properties of MIG Welds 100 Carbon Arc Welding 100 Atomic Hydrogen Welding 101 Resistance Welding 101 Pressure Welding 101 Joining Aluminum to Copper by Welding 101 Joint Design 102 Silver Solder Coating the Copper Bar 102 Procedures ' ~ 102 Physical Properties of Aluminum to Copper MIG Welds " 102 Exothermic Welding 102

SECTION V: Accessories Welding Fittings Bolted Accessories Tee Connectors Expansion Connectors Stud Connectors Bus Supports' ' Couplers and Terminals

105-116 ,

, .105-107 107 108-109 110-111 , .. 112-113 114-115 116

SECTION VI: Tables and Specifications . . , .117-168

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FOREWORD

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The wide acceptance of aluminum and its alloys in the electrical industry rests basically upon its economy and abundance. Aluminum's physical characteristics, such as high conductivity and light weight, give it unique advantages in Plany electrical applications where other non-ferrous metals formerly served exclusively. While the use of EC grade aluminum as bus bar dates back to 1895, the application of alloy aluminum bus conductor has been more recent. The various alloys and tempers now available provide a full range of properties, both elech'ical and physical, to meet practically any requirement. Aluminum bus bar is readily employed in proposed designs of new electrical systems and equipment and, in most cases, with only minor changes it can also be designed into existing systems. The primmy purpose of this book is two-fold: (1) to illustrate, describe and classify the numerous aluminum bus bar shapes and alloys now available; and (2) to assist the reader in making the most advantageous utilization of aluminum for various electrical bus bar applications. The versatility of aluminum bus bar as a rigid conductor is evidenced in the countless small installations designed to carry a few hundred' amperes to the extremely large facilities distributing currents on the order of 60,000 amperes. The smaller installations include rectangular bar in bus duct which provides service to machinery and equipment in many industrial plants. The larger facilities, such as chemical and reduction plants, require massive sections of bus bars to cany the high process currents. Selection of the most suitable alloy to provide both conductance and strength for the proposed usage is covered in Section 1. All of the common shapes of bus conductor offered by producers are described in detail. Fabricating processes, such as extrusion and cold rolling, are outlined to compare surface finish, strength characteristics, and dimensional tolerances inJparted to the alloys processed by each fabricating method. Electrical bus condu:ctor design is discussed in detail in Section II, while Section III presents mechanical design infOlmation to prove the adequacy of the proposed installation when subjected to short circuit forces and vibrational stresses, with or without additional loads such as wind pressure and accumulations of ice in outdoor conductor installations. Section IV offers methods of joining aluminum bus . C:ollductor both mechanically and by fusion processes. Emphasis has been placed upon the proper surface preparation to give low resistance, stable electrical joints; recommended bolting techniques are indicated. Fusion welding by four principal methods, .i.e., gas, metal are, tungsten inert-gas, and metal ineli-gas is described for applications where permanent electrical joints are prefened. Each welding process is covered in detail, including such subjects as preheating, edge preparation, and a practical method of welding aluminum to copper. j" Accessories commonly used for joining, supporting, tapping, and terminating bus bar are illustrated in Section V. These illustrations show the wide variety of installation methods possible with such accessories. Line drawings in this section indicate recent developments in welding fittings for bus conductor. Special attention is directed to the numerous charts, graphs, line drawings, and other illustrations. All have been handled with care both to simplify and augment text material. Numerous tables on bus bar physical and electrical properties provide a ready reference for design and application studies. . A comprehensive table of contents is presented under each section heading. July 1, 1957

ALUMINUM BUS CONDUCTORS

ALLOY CHARACTERISTICS AND PROPERTIES

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ing characteristics. The 59 EC temper is intended for . The abundance of aluminum ores and the rapid severe forming operations such as edge bending. Its eXpansion of aluminum production capacity are two forming properties are thus comparable to EC-H12. iUlportant factors that assure the electrical industry of a continued reliable supply of aluminum bus bar ma- These replacement alloys have somewhat less conductivity than EC grade confluctors, but their physical terials.. The reduction facilities necessary to produce properties and lower cost offset this disadvantage for ll,luminum from aluminum oxide (alumina) depend ·.upon large quantities of electrical power. It requires many applications. :N>proximately 9 kw-hr of electrical energy to produce one pound of aluminum. Since the production costs of electrical power are inherently stable, the price of Physical Properties of Aluminum .aluminum should also be stable. This is reflected in Bus Conductors ,the historical price pattern of aluminum. The many applications for aluminum bus conduc. ' As a result of this stability, aluminum has become tor demand a number of alloys with varied physical . ',the most economical of all conductor materials, and properties in addition to good electrical characteristics. .. because of this, a more extensive use of aluminum bus To supply the designer with this flexibility, several conductor has developed. Such conductor is finding its aluminum bus bar alloys are available that will pro,,!, way into manufactured electrical equipment of all vide physical properties to meet the requirements of kinds where its use heretofore had been considered most applications. This range of properties provides , neither feasible nor economical. Accompanying this alloys with high tensile strength at only a slight sacri'gradual spread of aluminum bus conductor into many fice in ductility for applications requiring high strength electrical usages has been the demand for performance but limited bending or forming properties. More duccharacteristics other"than those available with EC tile alloys for extreme bending or forming require(electrical conductor) grade aluminum. This trend has led to the development of several tempers of. a new . ments are also available where moderate tensile strengths are satisfactory. The physical properties of high strength bus bar alloy. The chemical composition these commonly used aluminum bus conductor alloys of this alloy conforms to the Aluminum Association are shown in Table L designation of alloy 6101. Four tempers of this bus These aluminum alloys have common physical conductor alloy have been developed to providl'l miniproperties important in the mechanical design of a mum conductivities of 55, 56, .57, and 59 per cent bus bar installation. One imp0rtant property is unit . . . (lACS) and physical properties superior to the EC bus weight as measured by density in pounds per cubic bar tempers which the new alloy conductors are reinch. Although other metal additions are made to placing. Kaiser Aluminum has designated these alloys some of the bus bar alloys, theYi are so small that, for as follows: all practical purposes, density. can be considered as 55EC (6101-T6); identical in all of· these alloys. The specific gravity 56EC (6101-T62); will thereby be a constant also. These properties are 57EC (6101-T61); given as: 59EC (6101-HIll). Density-lbs. per cubic inch-0.09765; The high strength tempers-55 EC and 56 EC-are Specific Gravity -2.703. replacements for EC-H17 and are intended for applications where only limited forming properties are deThe modulus of elasticity for all bus bar alloys can sired. The lower strength EC-H12 and EC-H13 alloys also be considered to have the same value, can be replaced by 57 EC and 59 EC which are more E = 10 X 106 (psi). ductile than 55 EC and 56 EC to provide better form-

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section I - general

TABLE .1 -

Alloy

PHYSICAL PROPERTIES OF ALUMINUM BUS CONDUCTOR ALLOYS

Minimum

Typical

Minimum

Typical

Typical Compressive Yield Strength (psi)

Yz

29,000

32,000

25,000

29,000

28,00.0

14

Vil- Yz

27,000

290 000

22,000

26,000

25,000

14

Thickness (Inches)

55 EC

Ys-

56EC 57 EC

Ys - 0.749 0.750 - 1.499 1.500 - 2.000

59EC

-

6061-T6

-

20,000 18,000 15,000 12,000 38,000

Vil- Yz

6063-T6

Ultimate Tensile Strength (psi)

30,000 33,000

Tensile Yield Strength (psi)

Elongation in 2 Inches (Per bent)

-

15,000 11,000 8,000

-

-

-

-

-

-

8,000

-

-

35

35,000

40,000

-

12

35,000

25,000

31,000

31,000

38,000

30,000

36,000'

36,000

10

12,000

10,000

35

-

45,000

-

12

6063-T83

0.050 - 0.150

EC-H12

Vil - 1

12,000

15,000

8,000

- % Ys- Yz

14,000

17,000

12,000

16,000

14,000

20

20,000

15,000

19,000

17,000

14

EC-H13

j~

EC-H17

-

EC-H111 EC-Hl12

Vil- Y2

lh - 1 1

- 1Yz

17,000 9,000

-

4,000

-

-

12,000 11,000 10,000

-

7,000 5,000 4,000

-

-

-

* * * *

-

*Elongation of these tempers will be equal to or greater than the elongation of EC-HI2.

Electrical Properties of Aluminum Bus Bar Alloys

TABLE 2 - PERCENTAGE VOLUME CONDUC· TIVITY (lACS) OF BUS CONDUCTOR ALLOYS AT 20 C

Conductivity-The selection of a bus conductor alloy for current carrying ability is based primarily on its electrical conductivity. In 1913, the International Annealed Copper Standard (lACS) was estabUshed based on annealed copper at 20 C and designating 100 per cent volume conductivity for a rod one meter in length and one square millimeter in cross section, having a resistance of 0.017241 ohm. This is the basis for establishing the percentage conductivity of other metals and their alloys. The percentage volume conductivity of these materials will be inversely proportional to the resistance of identical specimens at 20 C, e.g., the per cent conductivity of an EC (electrical conductor) grade aluminum wire one meter long and having the same one square millimeter cross section and a resistance of 0.028264 ohm at 20 C will have a per cent volume conductivity as follows: Per Cent Conductivity of EC 0.01724:1 100% - 0.028264 Per Cent Conductivity of EC = 61%. The per cent volume conductivity (lACS) for the common bus bar alloys is given in Table 2.

Thermal Properties of Bus Conductors

Resistivity-Resistivity is the reciprocal of conductivity and, like conductivity, is expressed on either a volume or a weight basis. Standard values for resistivity are also based on a temperature of 20 C. These values

Temperature Coefficient of Resistance-Standards for conductivity and resistivity are established for a tem.~ perature of 20 C, and d-c resistance calculations using these values will give resistance at 20 C. Conversi9n '

2

Bus Conductor Alloy

EC Grade (All Tempers) 55 EC 56 EC 57 EC 59 EC 6063-T6 6063-T83 6061-T6 1100 (Annealed) 1100 (Hard)

. . . . . . . . . .

Minimum

Typical

61 55 56 57 59 51

62 56 57 58 53 56 40 59 57

provide the basis for the calculation of. resistance of bus conductors according to formulas presented in the section on electrical characteristics. The resistivity of common bus conductor alloys is given in Table 3 in both units of volume and weight resistivity.

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general- section I

tABLE 3 -

RESISTIVITY (p) OF ALUMINUM BUS CONDUCTOR ALLOYS AT 20 C

. .

-

(Based on Minimum and Typical Conductivity Values)

'.

..

Maximum Values

~"'. : ,

EC Grade 610/0 Condue-

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tivity

,,"

57 EC 570/0 Conductivity

56 EC 560/0 Conductivity

Typical Values

55 EC 55% Conductivity

6063-T6 51~ Con uctivity

EC Grade 62~ Con tlCtivity

1100 Annealed 59% Conductivity

55 EC, 56 EC 1100-Hard 57% Conductivity

Wef~~t Resistivity

6063-T6 53% Conductivity

6063-T83 56% Con duc·tivity

6061-T6 40% Conductivity

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436.24 0.07640 ·¢!crohms-pound/feet' 15.65 ., ~Iuiis-pound/mile' .,. ¢~-gram fmeter' ..

466.85 0.08176 16.75

475.19 0.08322 17.05

483.83 0.08473 17.36

521.78 0.09138 18.72

429.20 0.07516 15.40

451.03 0.07899 16.18

466.85 0.08176 16.75

502.09 0.08793 18.01

475.19 0.08322 17.04

18.195 0.03025 1.191 14.29 3.025

18.520 0.03079 1.212 14.55 3.079

18.857 0.03135 1.234 14.81 3.135

20.336 0.03381 1.331 15.97 3.381

16.728 0.02781 1.095 13.14 2.781

17.578 0.02922 1.151 13.81 2.922

18.195 0.03025 1.191 14.29 3.025

19.568 0.03253 1.281 15.37 3.253

18.520 0.03079 1.212 14.55 3.079

665.27 0.1165 23.86

V:~~~e Resistivity ';ohms-cir mil/foot .... :Johms-sq rom/meter .. ·microhms-inch iIiicrohms--1.; Where: a

is the temperature coefficient of resistance

25.928 0.04310 1.697 20.36 4.310

to raise its temperature a given amount. On an equal weight basis, aluminum has a higher specific heat than copper. EC aluminum is 0.214 cal/gmrC and copper 0.0921 cal/gmrC. On an equal doc resistance basis, the thermal capacities are approximately equal. This high thermal storage capacity enables aluminum bus to withstand high overloads and short circuit currents. Test results show that under short circuit conditions, the bum-off characteristics of equivalent sizes of aluminum and copper conductors are similar. Specific heat values for a number of aluminum bus conductor alloys are: Aluminum Alloys

EC Grade 6063 55 EC (6101) 56 EC (6101)

Specific Heat

0.214 cal/gmrC 0.23 callgmr C 0.23 cal/gmrC 0.23 cal/gmrC

A. is the per cent conductivity (lACS) at 20 C.

TABLE 4-THERMAL COEFFICIENT OF RESISTANCE (a) AT 20 C

Aluminum Alloy

EC 59EC · 57 EC 56EC 55 EC 6063-T6 '"

.. . . . . .

Per Cent Volume Conductivity (lACS)

Thermal Coefficient of Resistance at 20 C

61 minimum 59 minimum 57 minimum 56 minimum 55 minimum 53 typical

0.00403 .0.00389 0,00376 0.00370 0.00363 0.00350

A more complete table of thermal coefficients of resistance is given in the section on electrical charac-· teristics along with examples of resistance conversions to other temperatures, see page 17. Specific Heat-The specific heat of a bus conductor material is a measure of the thermal energy required

Thermal Conductivity-The thermal conductivity of a material is its ability to conduct or carry away heat from a high temperature area and distribute and dissipate it. On an equal weight basis, aluminum bus conductor has higher thermal conductance than both steel and copper. On an equivalent resistance basis, the thermal conductance is comparable for both aluminum and copper bus conductors.}'-·

THERMAL CONDUCTIVITY AT 20 C (WATTS/IN2 IIN/SECI °C) Material

ECAluminum 59 EC, 1100 Soft 57 EC, 1100 Hard 56 EC, 6063-T83 55EC 6063-T6 6061-T6

....

Watts/in' /in/sec/oC

5.9 5.7 5.5 5.4 5.3 5.1 3.9 3

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section I - general

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:.;

'I "I

Effect of Heating on Tensile Strength-The generally accepted maximum continuous operating temperature limit for electrical bus conductor is 70 C. This maximum continuous operating temperature is established at an ambient temperature of 40 C with a conductor temperature rise above ambient of 30 C. These are the standard conditions used to e,stablish the continuous current ratings of bus conductors. These ratings are described in detail in the section on electrical characteristics, page 40. The effect of this 70 C temperature upon the physical properties of aluminum bus conductor is negligible. However, short time emergency conditions or high ambient conditions may cause conductor temperatures in excess of the normal 70 C operation, and the effects of heating' should be considered for such conditions. The effect of time at temperature on the hot and cold tensile' strengths of EC-Hl1 and 6063-T6 aluminum bus ,conductor is shown in Figs. 1 and 2. All alloys show a reduction in tensile strength at elevated tempera.wres. For EC-H17 alloy, tensile strength ranges from 20,000 psi at room temperature to approximately 10,000 psi at 200 C. Likewise, the tensile strength of alloy 6063-T6 falls upon heating, the extent depending upon the magnitude of the temperature as shown in Fig. 1. A similar behavior can be expected from 55 EC, 56 EC, 57 EC, and 59 EC.

These curves also show the effect of continued heating at elevated temperatures. The downward trend of the EC-H17 curves indicates progressive annealing. It is not significant until temperatures exceed 100 C where annealing just starts or proceeg.s very slowly. With rising temperature, the rate of an- . neal becomes progressively faster. At approximately 570 C, annealing is very rapid. Short time emergency overloads can be safely carried on EC aluminum bus conductor without seriously affecting its strength properties. At temperatures of approximately 150 C and below, the continued heating of 6063-T6 has the effect of artificially aging the alloy, and tensile strength.. may actually increase for a period of time before annealing is initiated. At temperatures exceeding 175 C, the continuous heating of 6063-T6 alloy produces an immediate reduction in tensile strength which is more pronounced than for EC-H17. The consequences of continued overheating of bus conductors must also be considered in bolted bus conductor joints where reduced clamping forces may result unless conservative methods of joining are used. These are described in the section on mechanical joining, see page 79. The cumulative effects of continued heating of aluminum bus conductors after they have cooled to

45000 , . . . . . - - - - , - - - - - - , - - - - - , - - - - - , . - - - - ,

45000 TENSILE STRENGTH AT ROOM TEMPERATURE AFTER HEATING

TENSILE STRENGTH AT ELEVATED TEMPERATURES

II

40oo01-----j----+----+----+----j

40000

35000 I - - - - - - - i - - - - / - - - - - t - - - - - + - - - - - j 65 C

35000

.1

6063 -T6

85 C

30000 r6:uJ "'''' -...OuJ 8

I

VAREA No.2

-

o ~.

V

/1

14

./V

/

1/

r/ V

V

_~~o,

AREA No.4

/

\

V

tR . .- TK

~'-~

/

'£. V

AREA No, 5

o

20

40

60

RATIO,

80

lOa.

120

140

OUTSIDE DIAMETER OF TUBE THICKNESS OF TUBE WALL =

160

180

200

0.0.

TK

Fig. 8 Area No. I-No Mandrel or Wiper Die Area No.2-Plug Mandrel and Wiper Die Area No.3-One Ball Mandrel Area No. 4- Two Ball Mandrel and Wiper Die Area No..5-Nat'Practical

Alloys-The high short circuit strength requirements of a square tubular bus usually require a heat-treatable, high strength alloy. Alloys 6063-T6 and 57 EC are generally used for this purpose. The cost and difficulty of drawing EC grade aluminum and the limited strength after drawing usually preclude the use of EC grade aluminum for square tubular conductor.

Channel and Angle Conductor Channels and angles used for bus conductors can either be rolled, extruded, or formed. These shapes may conform to the standard structural channel or angle section used in the steel indusby or they may be of special design for electrical applications. Where they are used for a-c buses, they are usually arranged to form a hollow square to provide an efficient elecb'ical configuration having a low skin effect resistance ratio. This is illusb'ated in Fig. 10.

T

..

l[JIO Courtesy Tal Bending Equip., Inc.

Fig. 9 - Field Bending

Square Tubular Conductor Square tubular conductors are used for applications reqt.Jiring high current carrying capacity and greater rigidity to resist extremely high short circuit forces. They are .used primarily for generator phase bus and for high capacity station bus. Courtesy General Electric Co.

I.

Electrical Characteristics-The current carrying capacity of square tubular conductor, like round tubing, is limited because of the smaller amount of exposed surface area for the dissipation of generated heat. To ventilate the interior surfaces, large holes are sometimes provided in the top and bottom surfaces to supply additional internal cooling by convectiop. air currents.

Fig. 10

The channel alTangements shown approximate square tubular conductor in both electrical characteristics and rigidity with the added advantage of providing cooling for the interior surfaces by convection. Current carrying capacity is thereby increased over an equivalent section of conventional square tubular con11

( I

I

;P-'=

section I - general

ductor. Where space is limited, such as in isolated phase bus, the special channels shown can be used to advantage. This is shown diagrammatically in the two equivalent sections, Fig. 10. The 5 inch special channel shapes arranged in box form have the same rating as the 7 inch standard channels. * In most cases, the size of the housing for isolated phase bus need not be increased when special aluminum channel sections are used.

!

I, ~

I

I I

il II' f

11'

,!, ;1] 1-. Ii

, .1

,

'I I.

:i1'1. i i'{ "j. ~ ,

\: )t

Applications-Standard channel conductor is used primarily for long span construction where a high current rating is desired and structural rigidity is necessary to withstand high short circuit forces. These sections can be used to advantage in outdoor substations and switching stations where a greater current capacity is desired than can be obtained with round or square tubular conductors. Channel bus conductor is also used in many low voltage, high current industrial applications for both a-c and d-c service. Typical of these applications is service to large rotating equipment, induction furnaces, rectifiers, and other mill installations having unusual current needs. It is also employed as bus conductor in industrial sub-stations and for bus ties between sub-stations or large electrical installations. Alloys-High current ratings, high short circuit forces, and long spans usually require high strength, heattreatable alloys such as 6063-T6 and 57 EC. Where even higher strength is desired and some conductivity can be sacrificed, 6061-T6 alloy may be used. For maximum conductivity, EC grade aluminum is preferred; however, the lower physical properties of EC aluminum must be considered in the design of supports, span lengths, and distances between buses. Usually the harder tempers of EC aluminum or a heattreatable alloy are most suited for a high capacity bus because of strength requirements..

t

~~ I

I

Ii 1

I

:1

II I:!: I' ~

t'

Other Conductor Shapes Special designs requiring non-standard shapes of bus conductor are readily fabricated from a number of aluminum alloys. These shapes, Fig. 11, may be produced by the extrusion process where a relatively

Fig. 11

simple extrusion die is required and the conductor thus produced will have close dimensional tolerances. The alloy selected will be governed by the physical and electrical properties required for the application and by cost consideration.

MANUFACTURING PROCESS AND TOLERANCES

!J, )

Fabrication-The broad flat surfaces of ch~umel and angle sections are used to advantage in joining sections of bus together. Flat plates may be bolted to both the inside and outside surfaces in either a straight splice or for making 90 degree angle bends. Prefabricated bus such as isolated phase bus is usually joined in this manner by bolting the prefabricated sections together in the field. Where standard channels and angles are fabricated on the job such as in an outdoor sub-station, these conductors are sometimes joined by welding. This method of joining is economical, particularly for the larger installations. Both methods of joining, either bolting or welding, give reliable elecbical joints when properly made.

.1

The methods of producing aluminum bus conductor generally fall into two classes: 1. Extruded bar and shapes; 2. Rolled bar and structural sections. Other methods are used to a limited extent for producing bus conductor. Among these is the casting method for producing large sections for high capacity bus. Bus conductor is also formed into various bus shapes from rolled aluminum sheet or plate. Drawn bus conductor is usually produced by one of the two basic methods of production indicated above and is an

* "Application of

Alumi.num Charulel Conductors for Station Bus," AlEE TECHNICAL PAPER 52-295, by E. J. Casey and N. Swerdlow, September, 1952.

12

added operation to achieve either strength, contoured edges, or dimensional tolerance. Each of the two general methods of production listed has its advantages and limitations, and discussion will be confined to these methods. The process used by the manufacturer in producing bus conductor should be the one that can most economically produce the quantity and the quality desired in the finished product. All of these basic production methods produce high quality bus conductor. The electrical properties of the conductor are not affected by the process used. The surface finish will be slightly different-each process producing its own inherent surface characteristics. Dimensional tolerances can be held to close

geneml- section I

limits with extruded or rolled bus bar. Cast bus bar has relatively larger tolerances.

Extruded Bar and Shapes The extrusion process is one of the most versatile used in producing bus conductor. All bus conductor alloys, both non-heat-treatable and heat-treatable, can be extruded into practically any shape desired. The process is particularly economical for the heat-treatable alloys which achieve strength through a heat treatment following the extrusion process. The nonheat-treatable alloys on the other hand, such as EC aluminum, must be cold worked to refine the grain structure and thereby impart greater strength to the "as extruded" material. This is done by cold drawing operations following the extrusion process in which the conductor is pulled through a die or series of dies, each being slightly smaller than the preceding one. The number of drawing operations required will depend on the amount of cold reduction necessary to produce the temper desired. The drawing operation is also limited by the shape of the section. Usually only the simple shapes such as rectangular bar, round bar, and round or square tubular sections lend themselves to a drawing operation. Irregular shapes create die design problems, and it is usually advisable to either extrude these shapes in a heat-treatable alloy, or as in the caSe of a standard structural section, it may be produced by cold rolling in rolling mill equipment.

Tolerances-Standard tolerances for aluminum extruded shapes and extruded rod and bar have been established by the Aluminum Association and applicable ASTM specifications. Aluminum Association tolerances are shown on pages 141 and 143 and are applicable to the average section. Column two tolerances in

the table on page 141 apply to all solid metal dimensions such as the thickness and width dimensions of rectangular bars and to all dimensions where 75 per cent or more of the dimension is solid metal. Standard tolerances for solid round bar and aluminum pipe are given on pages 124 and 126, respectively. The ASTM tolerances for EC aluminum rectangular bar in all tempers are shown on page 149.

Rolled Bar and Structural Shapes The production of rolled sections requires large rolling mill equipment which is not as flexible as the extrusion process. This generally limits the hot rolled and cold rolled bus conductor sections to standard structural shapes and flat or round bars. Edge contours on rectangular bar, other than square corners, are usually applied in separate edge rolling or drawing operations. The rolling process does offer advantages in processing wrought conductor alloys such as EC grade aluminum in rectangular or round bars and the standard structural shapes because cold working increases the temper of the material, imparting improved physical properties. Several tempers can be produced depending upon the degree of l~eduction in the rolling process. Hot rolled bus conductor is generally limited to rectangular bar which is sawed or sheared to width from hot rolled plate. In this form, it is designated as EC-H1l2. Although EC grade aluminum plate is commonly employed to produce hot rolled rectangular bar, commercially ptu'e almninum, 99 per cent aluminum which is designated as alloy llOO, can also be used. While dimensional tolerances can be closely controlled by cold rolling, greater dimensional accuracy and contoured edges usually require a drawing operation following cold or hot rolling..

Xl

t:

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13

-

--.~

---

-.

..= , ...

-'-'~~.,_

v

ELECTRICAL DESIGN OF BUS CONDUCTORS D-C RESISTANCE OF BUS CONDUCTORS

a

In long homogeneous conductor carrying a continuous current, the current is distributed through its cross section equally. The resistance is given by the formula:

R dc =

p

volume resistivity and weight resistivity corresponding to the per cent conductivity (lACS) at 20 C of aluminum and the various aluminum alloys used for bus conductor. For the per cent conductivity, (lACS), at 20 C of the various bus conductor alloys, see the table below.

L A ohms (at temperature, t)

in which R dc is the direct current resistance and p isthe volume resistivity of the conductor material, L is the length, and A is the cross sectional area, all at temperature, t. . This may also be written in terms of the weight resistivity, in which case it becomes:

R dc

= P WL

CONDUCTIVITY OF BUS BAR MATERIALS (Per Cent Conductivity (lACS) at 20 C) Material

EC (All Tempers) 1100-0

Minimum

Typical

61

62 59 57

1100-HIB

ohms (at temperature, t).

59EC 57EC 56EC 55EC 6063-T6 6063-T83 6061-T6 HD Copper

Here, p is the weight resistivity of the conductor material at temperature, t, and W is the weight of the conductor material ill either pounds or grams per unit of length consistent with the units of p. R dc is the d-c resistance at temperature, t. With these two formulas, the d-c resistance of a conductor can be calculated when the value of p is in any standard units. This means, however, that where p is given in ohms-cir mil/foot, the unit of area should be in circular mils and the length, L, should be in feet, or where p. is given as the weight resistivity in microhms-poundjfeetz, the weight, W, should be indi; cated in pounds per foot and the length, L, should be given in feet. The 'various values for p are shown in Table 1. This table lists the common units for both

59 57

•• .j'

i·

58 57 56 53 56 40 98

56 55

51

.,

Minimum conductivity is established by ASTM or company standards' and represents a guaranteed minimum conductivity for the respective alloy when purchased according to the governing specification. Typical conductivity values are not guaranteed. They are the representative values obtained from daily

TABLE 1 - RESISTIVITY (p) AT 2.0 C FOR BUS CONDUCTOR MATERIALS J"

% Conductivjty (lACS) at 20 C Aluminum Alloys Units Weight Resistivity

40%

Copper

51%

53%

55%

56%

57%

59%

60%

521.78 0.09138 18.72

502.09 0.08793 18.01

483.83 0.08473 17.36

475.19 0.08322 17.05

466.85 0.08176 16.75

451.03 0.07899 16.18

443.51 0.07767 15.91

20.336 0.03381 15.97 3.381

19.568 0.03253 15.37 3.253

18.857 0.03135 14.81 3.135

18.520 0.03079 14.55 3.079

·18.195 0.03025 14.29 3.025

17.578. 0.02922 13.81 2.922

17.285 0.02874 13.58 '2.q74

I /

61%

62.%.

98%

436.24 0.07640 15.65 .

429.20 0.07516 15.40

893.06 0.1564 32.03

*

Ohms·pound/mile" ... Ohms-gram/meter' Microhms-pound/feet'

665.27 0.1165 23.86

\

Volume Resistivity Ohms-cjr. mil./ft..... Ohms-mm' /meter .... Microhms-sq. in,fft... Microhms~cm. .......

*A

,

25.928 0.04310 20.36 4.310

?

i

~

....

. 17.002 0.02826 13.35 ~. 2.1126 ,,'

16.728 0.02781 13.14 2.2!l1 .

10.583 0.01759 8.31? I 059'

density of 2.703 is tak~n for ,aluminum far can'ductivity values 40-62 per: cent. A density of 8.89 is takeJ' for 98 per cent conductivity copper.

~.' -, ~

r!~ .-

I .70

(?

~

...

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(.~

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/. 16J. '

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/. / 3

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. . ;.IJ

section II - electrical design

D = 1250 mils; A = (1250) 2 = 1,562,500 circular mils; L = 1 foot (unit of length) ; P = 17.002 ohms-cir mil/foot at 20 C (for 61 per cent lACS); ,

production mllS. Typical values will exceed the guaranteed minimum conductivity by a margin which allows for a small variance in the composition or manufachlring process.

L

Calculation of D·C Resistance

Rae=PA;

To illustrate the application of the d-c tesistance fonnulas to the calculation of d-c resistance for common aluminum bus bars, refer to the following problem.

R de

Required: The d-c resistance at 20 C of the following bus bars in microhms per foot: A. Flat rectangular bus bar 4 inches X % inch of EC grade aluminum; B. A I1f4 inch solid round EC bus of 61 per cent conductivity (lACS); C. A 1 112 inch standard IPS extmded almninum tubular bus of alloy 6063-T6 with a typical conductivity of 53 per cent (lACS); D. Extruded aluminum alloy channel bus-4 inches-2.16 lb.-of alloy 6063-T6. Solution: I-A. The d-c resistance of a4 inch X lf4 inch flat rectangular bus bar of EC grade aluminum in microluns per foot at 20 C is calculated as follows: A = 4 inches X % inch = 1 square inch cross sectional area; L = 1 foot (unit of length) ; p = 13.35 microhms per square inch per foot at 20 C (for 61 per cent lACS);

" II'

k ,I I;

,j

,I

Rae

i

,!

, I

L

,j

1

I

= 13.35 microhms

per

foot at 20 C.

;i

I

I-B. The d-c resistance of a 11;4 inch solid round bus of EC grade aluminum of 61 per cent conductivity in microhms per foot at 20 C is calculated as follows:

!:

!I it

"

Laboratory Tests Being Made on Aluminum Bus Conductor

16

The d-c resistance of a 1% inch IPS extruded aluminum alloy tubular bus of 6063-T6 with a typical conductivity of 53 per cent (lACS) is calculated in microluns per foot as follows:

= 0.939

pounds per foot (table on page 126); L = 1 foot; P = 18.01 microhms-lb/feet 2 at 20 C (for' 53 per cent lACS) ; L Rae=PW; W

I ;

I

R de

=

1 18.01 X 0.939

= 19.2 microhms per

foot at 20 C. ' I-D. The d-c resistance of a 4 inch-2.16 lb. extruded channel section of aluminum alloy 6063-T6 in microhms per foot is calculated as follows: A

= 1.84 square inches

(cross sectional area), see page 132; L = 1 foot (unit of length); P 15.37 microluns per square inch per foot at 20 C (for 53 per cent lACS) ;

=

R de

= 15.37 X 1.~4 =8.35 microhms per foot at 20 C.

= P A:;

Rae = 13.35 X

6

ohms per foot at 20 C; = 10.88 microhms per foot at 20 C. l~C.

PROBLEM NO. 1

1 = 17.002 X 1,562500 = 10.88 X 10,

Temperature Conversion of D·C Resistance The heating or coolin b of an aluminum conductor produces a d-c resistance change which is linear

electrical design - section II

f· :

within the normal operating temperatures of the conductor. Graphically, this is shown in Fig. 1. The projection of the linear portion of the curve to the horizontal axis denoting zero doc resistance establishes a theoretical "temperature of inferred zero resistance." This "temperature of inferred ·zero resistance" will be a characteristic of each bus conductor material having a given percentage conductivity (lACS). To convert d-c resistance values from any temperature, such as the standard 20 C temperature, to another temperature within the normal operating limits where the above curve is linear, the following can be used: R tl = R t [1 + at (t, - t)]. Where: R tl is the doc resistance desired at a temperature, t , (in degrees C);

20 C as conductivity, resistivity, and basic resistance values are standardized at this temperature. In Table 2, the value of a is established for other operating temperatures. Care should be taken in the substihItion of a in the foregoing doc resistance conversion formula that its value and the known resistance are both for the same temperahlre. Due to skin effect and other inductive phenomena, a-c resistance does not follow the same linear relationship of temperature versus resistance that the doc resistance follows for the normal operating temperatures. To arrive at the a-c resistance at any value of temperahIre, the doc resistance should first be corrected to the temperatme desired, using the d-c resistance conversion formula. The a-c resistance can then be calculated for that temperature by methods shown in succeeding pages.

R t is the known d-c resistance at a temperature, t (in degrees C); at is the tempel~atme coefficient of resistance at temperature, t; (t , -.,. t) is the change in temperature in degrees C. ;,.

Temperature Coefficient of Resistance (a) The temperature coefficient of resistance represents the change in doc resistance per degree C. Its value will vary with the material, its percentage conductivity, and the temperature. The standard temperature coefficient of resistance is given for a temperature of

Temp. dcg. C. 0 10 20 25

o

·r

TEMPERATU RE

Fig. 1

TABLE 2 -.TEMPERATURE COEFFICIENTS OF RESISTANCE (a) FOR BUS CONDUCTORS 'MATERIALS' O( PERCENTAGE CONPUCTlVITY (lACS) 40% Condo

51% Cond.1 53% Cond.1 55% Condo

0.00279 ·0.00271 0.00264

0.00361 0.00349 0.00337

"il.6026i

ii:'Oo33I

0.00376 0.00363 0.00350 0.00344

I

0.00391 0.00377 0.00363

'D.Do'357

56% Condo

57% Condo

59% Condo

60% Condo

0.00400 0.00384 0.00370 0.00363

0.00407 0.00391 0.00376 0.00369

0.00422 0.00405 0.00389 0.00382

0.00430 0.00412 0.00396

0.00257 0.00251 0.00245 0.00239

0.00326 0.00316 0.00306 0.00297

0.00338 0.00327 0.00317 0.00307

0.00350 0.00338 0.00327 0.00317 __ _ _••:;0

0.00357 0.00345 0.00333 0.00322

0.00362 0.00350 0.00338 0.00327

0.00374 0.00361 0.00348 0.00337

0.00381 0.00367 0.00354 0.00342

70 80 90 100

0.00233 0.00228 0.00223 0.00218

0.00288 0.00280 0.00273 0.00265

0.00298 0.00289 0.00281 0.00273

- 0.00307 0.00298 0.00289 0.00281

0.00312 0.00303 0.00294 0.00285

0.00316 0.00307 0.00298 0.00289

0.00326 0.00315 0.00306 0.00297

0.00331 0.00320 0.00310 0.00301

Materials Aoolicable

6061-T6

Min. 6063-T6

1

Typical 6063-T6

Min.. 55 EC

atl

65ltTB~

Min. 57 EC

Typical 1100 Annealed

J

~

= desired thermal coefficient of resistance

62% Condo 98% Condo 0.00445 0.00426 0.00409 0.00401

0.00417 0.00400 0.00385

0.00387..... '0.00373 0.00360 0.00347

0.00393 0.00378 0.00364 0.00351

0.00371 0.00357 0.00345 0.00334

0.00335 0.00325 .0.00314 0J)!l30~

0.00340 0.00328 0.00318 0.00308

0.00323 0.00313 0.00303 0.00294

Typical EC-All Tempers

Represen.. tative Value for Commercial Copper Bus Bar

0.00438 0.00420 0.00403 0.00395

ii:'iiii38ii

30 40 50 60

Min. 56EC

61"fo Condo

M;" EC-All Tempers

Q.'6O'378

= known value of thermal coefficient of resistance = temperature in degrees C of known value of coefficient of resistance t, = temperature in degrees C at which desired coefficient is wanted.

at t

section IT - electTical design

A·C RESISTANCE OF BUS CONDUCTORS

When a conductor is used to carry alternating current, its resistance is apparently increased over its d-c value by several factors. This increase over the d-c resistance may be the result of one or more phenomena, each contributing an increment of resistance to the total a-c resistance of the conductor. The design of an a-c bus installation is influenced by such factors as skin effect and proximity which act independently of each other to increase d-c resistance. Losses due to induced circulating currents and hysteresis have a related effect on conductor a-c resistance in that both are incurred by the magnetic field of the bus conductor. In the over-all design of a bus conductor for a-c installations, thought should be given to all factors that contribute to a-c resistance. The major factors are: 'I. Skin effect This phenomenon is the tendency of current to concentrate more in the outer layers of the conductor thus apparently increasing the d-c resistance due to less efficient dist:ribution of the current in the conductor. The alternating current frequency, the conductor cross sectional shape, and its d-c resistance are factors that influence the magnitude of skin effect.

ij

2. Proximity effect This is the influence of nearby current carrying conductors on the current distribution in a conductor. When the current in two closely spaced conductors is opposite in direction at any instant, the current will be crowded toward the facing sides. When the current is in the same direction, it will be crowded toward the outer sides. This is shown diagrammatically.

II

:\ d 'j ,I I

,I:-

CURRENTS IN OPPOSITE DIRECTIONS

I I

00

jt

I: " i;'

Ii I~

Current Crowded Toward Facing Sides

I'

I;

Current Crowded Toward Outer Faces

The extent to which proximity increases d-c resistance depends upon the closeness of the spacing. The curves in Fig. 2 show the effect of proximity on the current rating of 55 EC rectangular conductors when spaced on 18 inch and 4 inch centers. Although a slight additional reduction in current rating at 4 inches is due to mutual heating, the majority is due to proximity. The 18 inch spacing may be considered as adequate for most

I: "

i!

,"

CURRENTS IN SAME DIRECTION

"

18

installations to reduce proximity to a negligible amount. 3. Mutual heating effects Mutual heating may be linked closely to proximity, but where proximity effect is the influence of the magnetic field of one conductor on a nearby conductor, mutual heating is due only to the interference of one conductor on the heat dissipation of the other. Close spacing, however, is not always indicative of mutual heating. On closely spaced, vertically arranged rectangular bars, the "chimney effect" created may actually aid in heat dissipation. Usually, however, closely spaced buses concentrate the heat produced by elements of the circuit and convection cannot dissipate this heat as effectively as it can when a greater separation is maintained. Less efficient cooling causes a more rapid temperature rise in the conductor and thereby reduces the current that can be carried for a given temperature rise. This phenomenon does not affect the RRac ratio of the bus. An equal degree of de

heating on either an a-c or d-c bus will produce like heating effects. 4. Induced circulating currents Induced circulating currents in nearby metallic parts require energy which must be supplied from the inducing circuit. This loss is accounted for by an additional component of resistance. The magnitude of this loss is a function of the distance to adjacent metal parts, the magnitude of the current flowing, and the resistivity of the metal part. Where such heating effects become excessive, e.g., in a common enclosure for a 3 phase bus installation, such as segregated phase or isolated phase bus, it may be necessary to make individual housings for each phase. 5. Hysteresis losses Hysteresis losses or magnetic heating is associated with the losses caused by induced circulating currents in that both are a result of the magnetic field of the conductor. This additional loss is also accounted for by an additional component of resistance. Where excessive heating is produced in nearby building steel, it may be necessary to band the steel sh'ucture with low resistance sh'aps or interpose an amortisseur grid between the bus and the steel to be protected. Losses in adjacent building steel will also be reduced by the presence of high circulating currents in metallic enclosures which separate the bus from building steel, as these circulating currents set up fields directly opposed to the conductor fields, thereby reducing the net effect. *

* "Temperature Rise

and Losses in Solid Structural Steel," O. R. Schurig and H. P. Kuehni, Journal AIEE, May 1926, pp. 446-453.


EFFECT OF CONDUCTOR SPACING ON CURRENT RATING 6101 Aluminum Bus at Spacings of 4" and 18"

6"xy"" RECTANGULAR BARS

V

V 3000

Current ratings are for bars arranged vertically and based on a 30 C temperature rise over 40 C

V

/

V

ambient in still but unconfined air.

/ V>

V

w

2000

...

:lj 2500

V

3"xlh" RECTANGULAR BARS

~'"

~ I-

u

J

. ~1"~

I

/

2100

~

I ~~

I Wi ",

I I I I I I

K

I

'"

w

'"a..w

lac

I

~; .'

r

r;;

I

/

';

,II

I

V-

V

I~ J

i' f'

I I

/'

I:

i

~'

.j

V

l/

/ ./

/'

\

Vl

W

~

-

\ \

~

"

/

~

,Vl

~/

,

\ \

;::-

i ~

I

V

~

i,

ti

r

/

R

,;

il

Rae Rdc

1200


normally would be smaller. A round tubular conductor is slightly more efficient than a square tubular conductor as currents will tend to be slightly greater at the corners of square tubing. The magnitude of skin effect increases with wall thickness in a round tubular conductor as shown

internal ventilation. As a result, standard shapes make an efficient bus conductor in the arrangements indicated and are used where high current ratings are desired.

by the RR ae curve in Fig. 10. For thin tubes, skin effect

Calculation of A-C Resistance

lie

conductor. The Rae curve, Fig. 10, shows this variation R rle for a 3 inch outside diameter tube of aluminum alloy 6063- T6 which has a typical conductivity of 53 per cent (lACS). The d-c resistance at 70 C as indicated in Fig. 10 is a function of wall thickness. When the d-c resistance values are multiplied by corresponding

The calculation of the a-c resistance of a conductor is based on the determination of the apparent increase in the d-c resistance of the conductor due to skin effect only, since this is the principal component that influences d-c resistance. For any given cross sectional shape, its d-c resistance, and the frequency of the circuit, skin effect can be evaluated independent of the conductor material and the parameters of the circuit. To find a-c resistance, the "skin effect resistance

. t ance ra t'10,"R va1ues a f t1le "k':ff s m e ect reS1S Ifae ,a curve

ratio," RR ae , is first determined. This ratio is a multiply-

is negligible and increases with wall thickness until it is a maximum where the tube becomes a solid round

(Ie

dc

giving a-c resistance is obtained. This a-c resistance curve, Rae, shows that a-c resistance becomes a minimum with a wall thickness of approximately 0.8 inch and increases slightly when the wall thickness is increased beyond this point. The current rating of this 3 inch diameter tube is also greatest at a wall thickness of 0.8 inch where a-c resistance is at a minimum as shown by the curve, lac. These curves are typical for all diameters of tubing having a conductivity of 53 per cent (lACS at 20 C). A-c resistance will be a minimum and the current rating a maximum at approximately 0.8 inch wall thickness for all diameters. Other materials will produce similar characteristics, but these optimum. characteristics will occur at a different wall thickness. Copper tubing (98 per cent conductivity lACS), has a minimum a-c resistance and maximum current rating when the wall thickness is approximately 0.5 inch and EC aluminum tubing (61 per cent conductivity lACS) at approximately 0.7 inch wall thickness. The effect of high conductivity of the material is to concentrate the current nearer the surface of the conductor. This means that a lower conductivity material fares better, with regard to skin effect; a given cross section is better utilized with current more uniformly distributed. It is sometimes possible to design a conductor of aluminum with the same outside diameter as one of copper, both with the same a-c resistance per foot. As a consequence, the same size fittings can be used. *

Channels and Angles Arranged in Box Form-These shapes arranged in box fonn, shown on page 11, approximate square tubular conductor in configuration. The web or leg thickness of standard sections is usually within the optimum limits where skin effect is at a low value. In addition, such shapes provide for

* "Aluminum in Heavy Current Conductors," 'VilJiam Paper 55-261, April 20, 1955.

Deans, AlEE Trans

ing factor that is used to modify the d-c resistance to obtain a-c resistance at the same temperature, e.g., Rac

=R

de

Rae R dc

X-.

The magnitude of the skin effect resistance ratio,

Rae' can b e determme : d convemen . tl y f rom curves:., R dc The following curves are used in this text as the basis for determining. skin effect for the common shapes of conductor, Fig. 11, page 24, skin effect in isolated rectangular bus conductors; Fig. 12, page 25, skin effect in isolated round wires and tubes; and Fig. 13, page 26, skin effect in isolated square tubular conductors. . Independent V ariable-The conductor shapes in Figs. 11, 12, and 13 have a common independent variable 'which is the abcissa on these graphs. The value of this independent variable is dependent upon the circuit frequency and the d-c resistance of the conductor at a given temperature, t. If the a-c resistance is desired at any other temperature, the d-c resistance must be converted to that temperature before the independent variable is calculated. The d-ch'esistance temperature conversion is shown on page 17. With the d-c resistance converted to the desired temperature, the calculation of tlle independent variable is then made by the following:

Where: Rde is the resistance in microhms per foot; is the frequency in cycles per second.

f

This establishes one coordinate for determining from

* "Electrical Coils and Conductors," H. B.

Dwight, McGraw-Hill Book Co.

23

lilillliililiililllll~

~

__..- ~._.~ . ~~=--.- ~

__.


CURVES FOR SKIN EFFECT OF ISOLATED FLAT RECTANGULAR CONDUCTORS I. 5

v

I

v

/ fl ~

1.4 I - - -

r---

/

t

~

~

I

I-

w.

/

I

II

/

J

)

If /

I I I 7 11 17

iJ ....

'.1

"-

~J

J /

./

J J

VhF! II

'0

J /f

I I 1 I /V II '/

1.3

II'

I

-$')

}

V

J

If

7

.../

7 J

/

/ VI /

If 'I iJlf

1.2

Ii / If V 'I

,j

J

J

j

'j

IJv

1.1

).

v

1/ /v 1.0

,.,.

ji ¥

\.

i ,;; !.

20

40

60

80

~ fx10 3

100

120

H. B. Dwight, "Elech'ical Coils and Conductors," McGraw-Hill Book Co.

.", l::

o

IN MICROHMS PER FOOT

j:

~

l----"V Rdc

L"

il:

/

Fig. 11

24

140

160

180


CURVES FOR SKIN EFFECT OF ISOLATED ROUND ROD AND TUBULAR CONDUCTORS 2. 1

2.0

t~

1.9

! - f--

1.8

ii;'

i'"

e

0

!:2

o· 0

'"

""'Ii "'t:I ~

-

-

'"""

0

1.7

t/ d' tid tid

O.~5

0

'"

0

::J

0.40

tid

1.6

I

o'

0.35

!:!

o'

0.30

!2 O' 0.

0

C::i

~

1.5

O'

&

O'

1.4

~

O'

~

O'

1.3

r;:,~ 1.2 Cl~

J;;P'

,1° 1.1

_0.0'1.

\/0.-

I,

tid-om 1.0

o

50

100

150

200

V

250

300

350

400

f•lO,

Rdc

Rdc

IN MICROHMS PER FOOT.

H. B. Dwight, "Electrical Coils and Conductors," McGraw-Hill Book Co.

Fig. 12

25


CURVES FOR SKIN EFFECT OF ISOLATED SQUARE ROD AND SQUARE TUBULAR CONDUCTORS

2.1

2.0

1.9

1

1.8

iI,

:11

,j:

"I: ~~ I,

1.7

'P

'i iii

J i,

1.6

Ii

~

I,

~

;,:

1.5 " J

t

.. I[

".

f

I

I

1.4 :

!

r " [

I

i

1.3

,;'I' ::

o

Ii

i;

I:: I..

1.2

i' I

II:

I:r, "

.1

I~ ,

1.1

I

I: t:

1.0

It;;

i~ ".

o

50

I {.i, .j

i:

150

200 r e 2 5 0 f,,103

Rdc

1

300

Rdc IN MICROHMS PER FOOT

Fig. 13

Ii

IIf: .

100

H. B. Dw;ghl, "Electrical Coils and Conductors," McGraw-Hill Book Co.

26

.J;

.

i:\

3.$0

400

450


curves the skin effect resistance ratio of the particular conductor section. The other parameter is a function of the conductor shape or physical dimensions, and its detelmination will be considered in the following paragraphs for the common bus conductor shapes.

curve representing the ratio ~

=

0.5 is the limitin

9

case for a solid square conductor. These curves may be used without appreciable error on channel bus conductors arranged in box form and also for angle conductors arranged in box form, Fig. 15.

Shape Parameter-The shape parameter is different for all of the foregoing conductor sections and is extremely variable because of the innumerable combinations of conductor dimensions. The graphical method provides for this variation by offering a family of curves to cover the practical range of bus conductors.

Rectangular Bar-The shape parameter for rectangular bar is the ratio of conductor width, W, to conductor thickness, t, in the same units of measure. The condition where Wit = 1 is the limiting case for a solid square conductor. Where several rectangular bar conductors are grouped together with a small separation between bars, a larger rectangular section is formed. The over-all dimensions of this section may be used with little error to establish the Wit ratio. For example, the Wit ratio for four rectangular conductors each G inches X Y4 inch spaced % inch apart will be as indicated in Fig. 14.

Fig. 15

The

dt ratio for the boxed channel arrangement

will be the ratio of the channel web thickness to the average outside dimension formed by the channels. For the boxed angle arrangement, the

~ ratio is the

ratio of the leg thickness to the average outside dimension formed by the two angles. These dimensions are listed on pages 133 and 135 for the standard clamps usually used as supports and spacers.

W

T=

6 1%

.. f Rac D elerlnluallOn 0 -R dc

= 3.425

With the independent variable calculated as described above and the shape parameter determined from the physical dimensions of the conductor, the Rae "k' . t ance ra t'10" can b e d etelmme . d '-R s m e ff ect reSlS de

Fig. 14

Solid Round and Tubular Conductors-The shape parameter for round tubular conductors is the ratio of the wall thickness of the tube to its outside diameter,

{Z, both in the same units of measure. The limit-

ing case

where~ = 0.5 is the curve for a solid round

conductor.

Square Tubula1' Conductors-The shape parameter for a square tubular conductor is the ratio of the wall thickness to its outside square dimension, _t. The

.

d

from the appropriate graph for the conductor shape. The shape parameter determines the proper curve from the family of shape curves and the independent variable establishes a point on this curve for which a ...:l ·(j)n t I1e or dinate sca Ie. · Rae correspon dmg - ra t"10 IS reaUj R dc To determine a-c resistance, the d-c resistance is multiplied by this ratio. This gives the a-c resistance at the same temperature, R ac = -Roc X Rde· Rdc To illustrate the calculation of the a-c resistance of aluminum bus bar, sample calculation is presented for several common conductor shapes.

a

PROBLEM NO. 2 Required: The 60 cps a-c resistance at 70 C in microhms per foot for the various bus conductor shapes illustrated in Problem No.1 on page 16.

27

section II - elect1'ical design

A. Rectangular EC aluminum bus bar 4 inches X % inch with a d-c resistance of 13.35 microhms per foot at 20 C; B. 1114 inch solid round EC aluminum bus bar with a d-c resistance of 10.88 microruns per foot at 20 C; C. Ph inch IPS tubular bus bar of alloy 6063-T6 with a doc resistance of 19.2 microhms per foot at 20 C; D. Two extruded channels 4 inches-2.16 lb. of 6063-T6 alloy arranged in box form with a d-c resistance of 8.35 microhms per foot at 20 C.

= 1.061

Rae

R de

and the a-c resistance is Rae

=r X

Rae

= 1.061

Rae

2-C.

,I

=

= =

t/fXT03 d and \/~mustbe calculated. These

[1 + a20 (70 - 20) J 13.35 [1 + (0.00403) (50)] 16.04 microhms perfoot at 70 C. R ae20

are given ~s follows for 11;2 inch standard IPS tubing:

t

~f

Rae

3

Rae

= 1.060

and the a-c resistance at 70 C is

R

Rae10

Rae = -R de

R ae10

= 1.060 X 16.04 = 17.00 microhms perfootat70 C.

de10

The a-c resistance at 60 cps of 1% inch solid round EC aluminum bus bar at 70 C is calculated as follows by determining first its d-c resistance at 70 C:

=

[1 + a20 (70 - 20) J [1 + (0.00403) (50)J 13.07 microhms per foot at 70 C. R

/

~ J:

o

~

'"

u

~ 30

~ ~V

/. ~ ~

I

en

.,:

o

.'0

~V

V

A-

.......!. -0

~ =5

/J ~~

v

~ 7d A

.... 25

« w

/I; II

U

z

« ....

t=O",-

u ~ 20

~ ~I t

'"

w

> ;::

If/;/

u

::> Cl

I

~ 15

.

"

-lAr-

B- 2

T-

"A -1

10

W

l~l--s--;1~

A_v: 8- 2

/iJ ~

I

5

IC

R

I

t=115

~ =1/10

/ o

-

8

8 -

//; I"r-..

/

~V

./

I 0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0 S

1.1

1.2

1.3

1.4

A+B Fig. 17 H. B. Dwight, "Electric JOUl'llal," Vol. 16, June 1919, Pages 255~256

1.5

1.6

1.7

1.8

1.9

2.0

I. '

.,.


INDUCTIVE REACTANCE AT 60 CPS OF WIDELY SPACED RECTANGULAR CONDUCTORS 95

90

85

C 0 u.

""w

80

0..

II)

::E :r

,

0

e; 75

(

I.....

~

I

.,; .,; 70

0 a

'0

...< w

65

V

Z

0

~

0 50

o"-

"""-w U'l40

/

~ J:

Inductive Reactance of Square Tubular Conductors and Channels in Box Form The inductive reactance of square tubular conductors can be determined approximately by the formulas an~graphs advanced by Dwight and Wang.* The

* "Reactance of Square Tubular Bus Bars," H. B. Dwight and T. K. Wang, AlEE Transactions. 1938. Vol. 57.

/

o u '"

~ 30

20 1

/

/

V

V

V

V

V

V

rCl

~,~

I I I III

2

3

4 RATIO

5

6

7

8

sic

Fig. 23 - Reactance of Thin Square Tubes

10 12 14

I

=


actance determined from this curve to correct for the wall thickness of the tube and for round comers usually present on commercial tubing. The curves in Figs. 24 and 25 provide the approximate corrections which are added to the reactance obtained from the curve in Fig. 23. 3.0

I

I

{OJ

2.5

~a==i

II)

w

U

>u 2.0 o-0

II

.... -
-

u

~ 1.0 .

.... -
;::

II

u

::::l 0

/

36

V I A

/ If

1/ tf

I

V kf

1/ A

20

VII / ~

Iwl.!ft.

STANDARD CHANNelS'

y~'"

V

3"_1.73#~ Lbs.

r;'

I

1/

V

~

l--:::::.;;::b::b::::~l/

5"-3.10~?:::....-::::~V

....... 1/

6"-4.48#::=:':::::% j

V

~

/ VVVV V V / 7 /: ~V; V / /

~~/

VVA I i

1/

A

A

II

/

V

....... 1.---"

8,,~.80~.%'

3

V

-

.

:

..... ~

I I I II

i

.

4

V

I

II

~c:V 0

~ ~ II

/j 'V0

/:

receiving-end voltage;

= a-c phase current; = impedance angle; e = power factor angle;

I ¢

IZ = impedance voltage drop. The magnitude of the sending-end voltage for a given load and load power factor angle, e, is obtained by the following formulas:

39


E s == \I (E,. cos ()

+ IR)2 +

(Ersin ()

+ IX)2

cos () = 0.9

() = 25.83 degrees

( Generated voltage to neutral)

,/3E. == (Generated voltage phase to phase).

= 0.4359 IR = (728) (17.00 X 10-

sin ()

PROBLEM NO. 5 The application of these formulas to a typical bus installation is offered in the following problem using the resistance, reactance, and impedance values calculated in previous problems.

IX

Required:

=

Solution: With 440 volts available at the load, the sending-end voltage is desired to determine if the installation is within the 2 per cent voltage drop required. watts 1- \13 X volts X pf 500,000 1== (\13) (440) (0.9)

== 728 amperes

(100)

= (728)

(59.4 X 10-6 ) (100) = 4.32 volts

IZ = (728) (61.8 X 10-6 ) (100) == 4.50 volts

It is required to supply rated power to a 440

volt, three-phase, 60 cps load of 500 kw at 0.9 power factor lagging without exceeding a 2 per cent voltage drop. The bus consists of one 1/4 inch X 4 inch EC aluminum bar per phase in a run 100 feet long. The elecb:ical characteristics of this installation have been illustrated in part A of Problems 2, 3, and 4, as follows: a-c resistance, R == 17.00 microhms per foot at 70 C; reactance, X = 59.4 microhms per foot; impedance, Z = 61.8 microhms per foot at 70 C; impedance angle, ep 74 deg., 2 min.

6)

== 1.24 volts

Er .

\13

+ 11)2 +(Ersin + 1x)2 11[(254.0) (0.9) + 1.24)2 + [(254.0)

E s == V (E r cos

=

= 44~ = 254.0 volts (line to neuhal)

(J

(J

(0.4359)

+ 4.32)"

= 257.0 volts to neutral at switchboard E8 Es

== (257.0) \13 = 445.1 volts (line to line) -

E r =445.1- 440

== 5.1 volts (actual voltage difference) A 2 per cent voltage drop required for this installation would be: (440) (0.02) ==8.8volts. The actual voltage difference of 5.1 volts is lower than the 8.8 volts that represents 2 per cent voltage drop so that the installation meets the requirements for voltage drop. The current carrying capacity of a 4 inch X 1/4 inch bar arranged vertically is listed as 1000 amps for a 30 C rise over ambient when installed in still, but unconRned air, so that this installation also meets the requirements for current rating.

CURRENT RATING OF BUS CONDUCTORS In the majority of bus conductor installations, temperature rise of the conductor is the limiting factor. Since bus conductor runs are usually short, voltage drop and energy loss are usually not important factors. This is particularly true on high voltage installations. However, at the a-c distribution voltage level and on low voltage d-c bus where very high currents are encountered, voltage drop and power loss may be important factors. Industrial a-c bus runs utilizing voltages less than 600 volts fall in this latter class. For any given surface condition, i.e., fixed emissivity, the temperature rise of a bus conductor is affected by the magnitude of the current flowing and the resistance of the bus bar. These two factors govern the amount of heat generated within the bus conductor 40

and are directly responsible for increasing the temperature above its surroundings. This generated heat within the conductor is dissipated by two means-the radiation of heat to other bodies located nearby and by air currents which become heated and carry away heat either through natural convection currents, as in a closed room, or by forced air circulation such as a light breeze or wind in an outdoor installation. The difference in the latter two quantities, i.e., the loss due to natural convection air currents or the heat loss by forced air circulation, determines the indoor and outdoor current ratings respectively of bus conductors. Temperature limits for a bus conductor must be established such that continuous operation is possible with a reasonable factor of safety for the bus itself

electl'ical design - section II

and for equipment connected to the terminals of the Where: bus. Where equipment ratings are based on a 30 or J2R represents the heat generated in the conductor 35 C rise, the bus rating is usually limited to the same in watts per unit of length; temperature rise. The bus and the connecting leads to W, and We represent, respectively, the heat loss by this equipment, then, will not operate at a higher temradiation and convection in watts per unit of perature and conduct heat into the equipment, thereby surface area; raising its normal operating temperature. A represents the surface area per unit of length of The physical properties of rolled or drawn prodthe conductor. .ucts, i.e., tensile strength and yield strength, may be The above formula solved for the current, I, gives: sacrificed by excessive heating, and temperature limits should be established with due regard to the thermal I(W, + We) A properties shown on page 4. Expansion lengthwise of 1= '\j Rae amperes. the bus conductors may also become a problem on long bus iuns. Expansion fittings and flexible connecWhen the a-c resistance, Rae, is given in microhms tions are used to compensate for elongation of the bus per foot, the heat losses W, and Weare given in watts members so that strains are not imposed on supporting per square inch of surface area, and the diameter of insulators and equipment terminals. The reliability of the conductor, in inches, replaces the surface area per electrical connections to bus conductors may also be foot, A, I then becomes: affected by high current densities and excessive heating. This is discussed in the section on the joining of 37.7 (W, + We) D X lOG 1= R amperes. bus conductors. ae . To determine the current rating of a bus conductor, it is necessary to establish an ambient air temperature and a maximum safe continuous conductor operating ""'Heat Loss by Convection-Outdoor Rating-The temperature. These temperatures determine the perheat loss due to convection air currents is based on a missible temperature rise over ambient. The continuminimum value of wind velocity which is generally ous current that is required to produce equilibrium at taken as 2 feet per second. This is from 5 to 10 times this established temperature rise is the nominal curthe estimated velocity of air currents due to ·free conrent rating of the conductor. Usual procedure is to use vection, but is a low value for usual outdoor wrnd velocities. Heat loss by outdQOf convection currents is: a 40 C ambient air temperature and a maximum safe continuous operating temperature of 70 C which 0.0128 V PV M . means that a 30 C temperature rise is the limiting We watts per square mch, T aO.123 IjD condition. Once the temperature limits have been established, Where: other variables that affect the current rating must also P absolute air pressure be taken into account. Such variables as wind velocity, (P = l.0 for atmospheric air pressure); emissivity of the conductor surface, atmospheric pressure, the effect .of sunlight, and bus enclosures should V = cross-wind velocity in feet per second; be considered. M = te~perature rise of the conductor above ambient in degrees C; . T a = T +2 To is the average ab soIute temperature 10 Current Rating of Round Conductors

~

=

=

The Schurig and Frick * method of calculating the degrees Kelvin betl'veen conductor and air current carrying capacity of round conductors is gentemperatures; erally accepted as the method which approximates D = the conductor diameter in inches. field conditions and gives proper weight to the above factors. The effect of sunlight in raising conductor v'Heat Loss by Convection-Indoor Rating-The intemperature has been found to be small on loaded door ratmg of a bus conductor is considerably lower conductors and is neglected in this method of calthan the outdoor rating because the heat loss due to culation. . natural convection air currents is lower. Thus, the This method essentially balances the heat generwatts dissipated from a cylindrical conductor indoors ated in the conductor by I2R losses against the heat -free convection-for any temperature rise and any loss by convection and radiation. The general formula ambient air temperature is: for the steady-state condition is: 17.5 X 10-G T aO.754 M VI>

We =

* "Heating and Current Carrying Capacities of Bare Conductors for Outdoor

Service," Schurig and Frick, GENERAL ELECTRIC REVIEW, VoL 33, No.3, March, 1930.

D Ln

[0.0031 T aO.941 Do.s1 f:"t O•27

+1

]

watts per square inch.

41

section II - electl"ical design

For the standard conditions of 30 C temperature rise over a 40 C ambient air temperature at atmospheric pressure, this becomes: 0.01805

We ==

D Log10

watts pe1' square inch.

[0.298] DO.81 + 1

When D is more than 3 inches, an approximate relation for the convection heat loss indoors is:

We

0.14 = DO.19 watts per square inch, approxima.tely.

W _ 0.0128 e -

yW t"t' y'D

Ta,0.123

.

Where: P = atmospheres (air pressure) usually taken as

1; V == cross-wind velocity-2 feet/second; == temperature rise-30 C above an ambient of 40 C; Ta, == average absolute temperature of conductor and ambient temperatures; t"t

== 70; 40 + 273 == 328 K; Heat Loss by Radiation-The radiation heat loss, W n for both indoor and outdoor installations can be calculated as:

W 7 == 36.8e

[C~O Y- (1~~0 y]

watts per square inch. Where: e is the surface emissivity constant-usually given as 0.35 for indoor installations and as 0.5 for outdoor bus with average tarnished metal surface, Black non-metallic surfaces have greater emissivity and 0.9 is generally used; T is the absolute temperature of the conductor in degrees Kelvin; To is the absolute temperature of the surroundings in degrees Kelvin-usually taken as absolute air temperature.

In the case of outdoor installations, bus conductors are subject to more corrosive conditions and the degree of surface tarnish will have an influence on its ability to radiate heat to surrounding objects. This factor is taken into consideration by the term e which represents the emissivity of the surface of the conductor. For outdoor installations, e is generally taken as 0.5; while for indoor bus conductors, the average emissivity has been found to be approximately 0.35, Bus conductors are sometimes painted with a flat nonmetallic paint to increase their emissivity. This is discussed on page 49.

.~

Method of Calculation-The indoor and outdoor current ratings for a 1 ~ inch IPS extruded bus conductor of alloy 6063-T6 are determined as follows for a 30 C temperature rise over 40 C ambient air temperature:

=

Diameter D 1.900 inches; A-C resistance at 70 C = 22.57 microhms per foot; Emissivity e 0.35 for indoor rating; 0.5 for outdoor rating.

,1,1

; I;· . IR':

=

Outdoor Rating The outdoor rating for this conductor is calculated as follows: 42

W- (0.0128) y(l) (2) (30) . (328)0.123'11.9

e-

'

= 0.1931 watts per square inch;

C~O)' - C~~O)']

W 7 = 36.8e [ watts per square inch. 'Where:

T == 70 + 273 = 343 K, conductor temperature in degrees K; To == 40 + 273 == 313 K, temperature of . surroundings usually taken as ambient air temperature in degrees K; e == 0.5 for outdoor installation; W,. == (36.8) (0.5) [(0.343)4 - (0.313)4]; == 0.0781 watts per square inch; We

+ W == 0.1931 +

0.2712 watts per

0,0781 square inch;

7

!( 37.7) 1= '\j

(0.2712) (1.9) lOG 22.57

= 927.8 amperes or 930 amperes. Indoor Rating W _ e-

0.01805 [0.298 D Log10 D 081

+1

0.01805 0.298 1.9 Log10 [ 1.90.81

]

+1

]

= 0.1341 watts per square inch W 7 = 36.8e

[(l~OY - C~~O)']

= (36.8) (0.35) (0.00424) = 0.0546 watts per square inch


We

+ W r = 0,1341 + 0.0546 = 0.1887 watts per square inch 1

=

/37.7 (We

+ Wr )

'\j

D

X

106

Rae

/(37.7) (0.1887) (1.9) 106 - '\j 22.57 _

=

770 amperes

Limitations of Round Conductors-Solid and Tubular-Round bus conductors do not have the disadvantage of requiring orientation with respect to convection air currents for dissipating l"R heat losses. This advantage is offset by the limited amount of exposed surface area on a round conductor. In tubular conductors, the internal surface does not contribute to the dissipation of heat unless methods are provided for circulating a cooling medium. This is not practical for most installations. A small variation in the cunent rating of a tubular conductor can be achieved by varying the wall thickness up to its optimum value, page 22. Wall thicknesses greater than optimum do not add to its current canying capacity. The efficiency of a tubular conductor with a given outside diameter can only be improved by changing the denominator of the efficiency formula, i.e., by lowering the a-c or d-c resistance by increasing the wall thickness up to its optimum value, as surface area remains constant. This is shown by the following relation:

that a rectangular bar of given dimensions and material will have one current rating when arranged with its width vertically and another rating when its width is arranged horizontally. Other intermediate ratings will depend upon the angle the flat sides of the bar make with the horizontal or vertical position. Rectangular bar lacks the symmetry of a round conductor; hence, the dimensions of a rectangular bar-its width and thickness-also affect CUlTent rating in addition to the orientation. Each is discussed in detail. Effect of Width of Bar on Its Current Rating-Since the exposed surface area is more a Mlction of the width of the bar than the tIlickness, changing the width of a bar increases surface area and enhances its ability to dissipate heat. The most efficient rectangular conductor is one that has the highest ratio of exposed surface area to a-c resistance or to d-c resistance for direct cun-ent applications. This is expressed simply as: . exposed surface area/unit of length E ffi Ctency = . /um ' t 0 f lengt}~ reStstance Changing the width of a rectangular bar increases efficiency by affecting favorably both the numerator and denominator in the efficiency formula. The exposed sUlface area is increased and a-c resistance is decreased, both of which increase the efficiency of the bar. Table 3 gives current ratings of various sizes of bar to show the effect of varying tile width of a bar rather than its thickness.

Current Rating of Rectangular Bar The alternating cunent rating and the direct current rating of an aluminum rectangular bar with its width arranged either vertically or horizontally is available from tables for standard design conditions, pages 118 and 119. It is apparent from these tables

I I

,j

~i

I

I/,~

( J

I

Effie' exposed surface area wncy = a-cor d-c resistance . It is impractical to design for maximum efficiency in most instances as this will require a large diameter tube to increase surface area, with a thin wall to give a maximum of surface area per unit of cross section. The design and selection of a tubular conductor is often dictated by the cost of the accessories used to support, tap, and join the lengths together. From filn accessory cost standpoint, good design will usually indicate that an aluminum tube with a wall thickness approaching optimum, see page 22, will allow the replacement of a standard copper IPS conductor with the same outside diameter aluminum tube. Solid round aluminum conductors are practical up to approximately 2 inches in diameter for a-c applications while any size is suitable for d-c operation, see page 125.

I j I

I'

TABLE 3-CURRENT RATINGS (Rectangular EC Aluminum Bar, Arranged Vertically)

Size

A-C Current Rating * (Amperes)

3X ~ 4 X 14 3X %

775 990 955

f

Cross Sec- Surface Area Current tional Area Per Foot Density (Square (Square (Amperes Per Inches) Inches) Square Inch)

%

1

IVa

78

1033

102

990 849

81

* 30 C temperature rise over 40 C ambient in still but unconfined air.

The 60 cps alternating current rating of a 3 X ~ inch rectangular bar arranged vertically is shown to be 775 amperes. The most desirable shape for a replacement bar in order to increase tile current rating to approximately 1,000 amperes would be to select a bar of increased width rather than thickness. The tabulation shows that a 4 X ~ inch bar has a current rating of 990 amperes and a cross sectional area of one square inch. An increase in the thickness of tile original bar to % inch, with the width remaining at 3 inches would provide a ba~. with greater cross sec43


tional area-tVa square inches, while sluface area is increased by only 3 square inches, thus giving a rating of 955 amperes. The use of a 4 X 14 inch bar for the required rating provides a significant increase in surface area-24 square inches per foot, and yet only increases cross sectional area from % to 1 square inch. It is not practical in most installations to pursue the ultimate in efficiency as space limitations often dictate conductor dimensions. A wide thin rectangular conductor, although quite efficient, is obviously not suitable in modem installations. Some degree of latitude in design, however, may be used to take advantage of a slight increase in the width of a rectangular bar. In multiple bar installations, somewhat greater efficiency may be obtained by using more bars of reduced thickness to provide more total surface area between laminations.

Effect of Bar Thickness on Current Rating-From an efficiency standpoint, a change in the thickness of a rectangular bar is not as effective as a change in width as only the resistance is changed without appreciably affecting the amount of exposed surface area. In the efficiency formula, this means that a change in thickness affects primarily the denominator. Since the thickness, t, of the bar is proportional to the cross sectional area, A, for a constant width, W; and the d-c resistance is inversely proportional to cross sectional area:

Wt 1 = A 1 Wt 2 A 2

=R

2

R1

and t 1 t2

=R

2

•

R1

Two bars of the same material, having identical widths, but slightly different thicknesses, possess nearly the same exposed surface area for heat dissipation. These two bars will necessarily generate and dissipate nearly equal amounts of heat to maintain like operating temperatures. This means the J2R losses will be approximately the same for each bar, i.e.:

11 12 =

/2'

\iT = 1.41.

A comparison of the actual current ratings of two bars of equal widtll but with a thickness ratio of 2 to 1, shows a close correlation of the above ratio to the actual ratio of their direct current ratings, e.g., EC aluminum bar, 8 inches 2720 amperes d-c; EC aluminum bar, 8 inches 1920 amperes d-c;

11 2720 12 = 1920

X ~~

inch-

X ~~

inch- .

= 1.417.

A comparison of their alternating cun-ent ratings will show a slightly different ratio due to the influence of skin effect. The actual ratio of the a-c ratings of these bars is 1.34.

Effect of Position on Current Rating-The effect of position on the current rating of a rectangular bar is very pronounced. Where the long flat sides of a bar are arranged vertically, the convection air currents pass upward along the sides of the bar and thereby efficiently canoy away the heat generated by the J2R losses. The horizontal anangement of a rectangular bar prevents the rising convection air currents from contacting the large flat surfaces of the bar which present the greatest exposed area for natural ventilation. The curves in Fig. 29 show the difference in the current rating of a single bar when arranged both vertically and horizontally. 2000 , - - - - - - - , . . - - - - - , . - - - - . . - - - - , - - - - ,

1600 I------il----+----+~,L:.._=..-l"'::::;;..-----l

11 2 R 1 = 12 2 R 2 • Where: 11 2 R 1 is the heat generated in one bar; 12 2 R 2 is the heat generated in the other. A ratio of the currents in the two bars will be:

." 1200. UJ

'" "" ~ UJ

800 ~~~~f=-----+----I----+-~----j

11 2 R 2 11 /R 2 12 2 =R 1 and 7;= VR 1 ' By substitution, the relation between bar thickness and current rating will be approximately,

400

1-----1I--'---+----t---+----j

OL_ _-L_ _-.L 3x!4

5xv..

--L-_ _--L_ _----'

6xv..

7xv..

SIZE OF BARS

The relation between two bars of equal width, where one bar is twice the thickness of the other, will be approximately 44

Fig. 29 - Effect of Position on Rating NOTE: Ratings are for 30 C rise over 40 C ambient temperature in still but unconfined air.


ALTERNATING CURRENT RATING AT 60 CPS*

OF MULTIPLE COPPER AND EC ALUMINUM RECTANGULAR BARS 7000

6000

1f.I "x6" BARS-..........

t---..

5000

o z

~ ~ 4000

"l

w

DVl7 ic

","-

w::E

:t «

o

3000

u

0

VB

2000

~

~

G&H

0

N___

0

5000

R

Q

p

o

o

.~

4000

4;

'"

(M

::E

3000 ~ ::>

"-

""z w -

1f.I"x4" BARS

c.. :::E :::E::>

J

2000

F

4; -' 4;

C---< ~

u

w

A

1000

o

V

V ~ "" /0 ~

;::'"

N

I,.--"

1000

s:

0 1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

CD

n

16

:r

NUMBER OF BARS

III ~

n',

!!!.:

ARRANGEMENT OF BARS

I

A

II

B

I I I

c

"I I

E

III II

r

I II

I I

F

/II

I

G

"I

II

f--",,-j

H

II I

II

0

I

II

I

I II I

/I

J

1111

/I

I

II

/'

/I /I /I II

I

N

I:,;;~

II II

Il'!L

III' III /I

J

/I II

p

II II

II II II

II

II

I I

I M,

II II

I

"'II "'II III III III

II II /I

f--18"~

"

Q

"' "'

'"

""

1/11

""

"II

R

~.;

l' J iJ

""

/1/1

f--",,-i

I'J'~ "i

I

I"

1/1

*

inch. Large spacings between bars are 2% inches.

Fig. 30

fi

1

.

1

j' Ii•if ~

;f'

) r.

1/l u If i" " §nu j

l'r

'"

/III

i:,J

/III

;1

:/

'I'

t" (I

IJ

j: , I:: '

!

:'"

iiI' i~

* For a 30 C temperature rise over 40 C ambient in still but unconfined air. Ratings are for single phase in the multiple arrangements shown above. NOTE: Small spacings between bars are

~

,

1111 K

oti'

I

I

I /I"

0

0 CD ur

i

I'

1:1" : I: I! I' "

'

(IT

,45

'! ,f

,I

"

fl

;, :~

..__.__ ~_JUJ1: '


Current Ratings of Multiple Bar Arrangements A great deal of experimental work has been done in determining the current ratings of copper rectangular bus bars in the many' arrangements being used. These values can be used to determine the current rating of aluminum rectangular bars where the same number and size of aluminum bars are arranged as the copper installation. These copper ratings, however, must be reduced by the conversion factors shown in the table on page 47. These factors will be accurate for d-c conversions and conservative for alternating current ratings. Where a more exact alternating current rating is desired, the direct current rating should be modified to correct for the skin effect resistance ratios of the buses. For example, if the d-c rating of a copper rectangular bar is given as 2000 amperes and the d-c rating is desired for an identical bar in EC aluminum, the conversion factor from the table for the copper bar in terms of the EC aluminum bar at 70 C is 1.273, using EC aluminum as the base value of 1.000. The EC aluminum rating then at 70 C is as follows: 2000 1.273

= 1570 amperes for EC aluminum.

If the d-c rating is desired for the same construction in 55 EC aluminum bar, this is determined from the conversion factor of 0.958 in the same table which gives: 1570 X 0.958

= 1500 amperes for 55 EC aluminum.

To facilitate this conversion for the 60 cps ratings of 4 X lf4 inch and 6 X lf4 inch rectangular bars, the published curves * of copper ratings are reprinted as Fig. 30, with a scale added for the ampere rating of EC aluminum bars. The 60 cps ratings for EC aluminum bars can be converted approximately to other aluminum alloys by the d-c conversion factors in Table 4. Such values will be conservative for aluminum alloys of lower conductivity. Standard replacement sizes of aluminum bars have been designated by Underwriters Laboratories Inc. in their "Standard for Dead-Front Switchboards." These sizes are shown to the right.

Current Rating for Square Tubular Bus The current ratings for square tubular bus are indicated on page 136. Where a ventilated square tubular bus is used, these current ratings can be increased by 15 to 20 per cent. Ventilation is obtained by drilling holes in the top and bottom surface of the square tube to allow convection air currents to pass through the interior section of the bus. These holes are staggered

* "Current

Carrying Capacity of Bus Bars," H. W. Pabst, ELECTRICAL WORLD. September 21, 1929.

46

for maximum effect at intervals of approximately 4 inches. Holes normally are Ilf4 inch diameter for the 3 inch square hlbe and range in size to 1% inch for the 6 inch square tube.

Current Rating for Standard Channels and Angles The current ratings for standard channel shapes arranged in box form are shown on page 133; the current ratings for angles arranged in box -form are also indicated, page 135. The current ratings for standard channel shapes not listed are best determined experi~ mentally.

Current Rating for Non-Standard Bus Shapes The current rating of non-standard shapes should be determined experimentally where an accurate determination is required.

Conversion Factors Many tables give the resistance and current rating of a bus conductor in terms of a particular material or alloy with its conductivity based on the International Annealed Copper Standard (lACS) at 20 C. It is often desirable to know the characteristics of an identical conductor when fabricated of another metal or alloy when only its conductivity is specified. Conversion factors may be used to convert standard values such as the resistance and current rating of one metal to the other without starting from basic values. These values apply only to a given conductor size and shape, i.e., a conductor of equal dimensions and cross sectional area, see Table 4. This table of conversion factors applies essentially to the d-c constants of a given size and shape conductor. In many cases, the direct current rating is of sufficient accuracy that it can be substituted for the BUS BAR CURRENT RATINGS FOR DEAD-FRONT SWITCHBOARDS * Bus Bar Rating in Amperes

225

400 600 800 1000

Minimum Dimensions of Bus Bars in Inches Copper

~by

%

lf4 by IVz Y4 by2 Y4 by3 Y4 by4

Aluminum

Y4 by % Y4 by 2 Y4 by3 Y4 by4 lf4 by 6 or two Y4 by 3

A minimum tolerance of five per cent in the cross sectional area is allowed for rounding and shaping a bus bar. A bus bar having other dimensions may also be acceptable if it has not less than the cross sectional area specified in the table and has equivalent rigidity.

* Underwriters boards."

Laboratories "Standard for Dead-Front Switch-


TABLE 4 - CONVERSION FACTORS FOR IDENTICAL SHAPES BUT DIFFERENT CONDUCTOR MATERIALS (EC Aluminum -

55 EC Minimum

6063-T6 Mini- 6063-T6 Typical 6061-T6 mum

Bus Conductor Material

Per Cent Conductivity (lACS) ..... 40 Equivalent Conductance at 20 C ...... 0.656 Equivalent d-c Resistance at 20 C ...... 1.525 Equivalent d-c Resistance at 70 C* . .... 1.437 Equivalent d-c Rating 0.834 at 70 C. '" .. Equivalent d-c Voltage Drop at 70 C ...... 1. L98

* Resistance

61 Per Cent Conductivity -

51

55

53

as a Base)

56 EC 6063-T83 1100-H18 1100-0

56

57

59

EC

61

Hard Drawn Annealed Copper Copper MiniMinimum mum

98

99

lACS

100

0.836

0.869

0.902

0.918

0.934

0.967

1.000

1.607

1.623

1.639

1.196

1.151

1.109

1.089

1.070

1.034

1.000

0.622

0.616

0.610

1.170

1.126

1.089

1.074

1.060

1.028

1.000

0.618

0.613

0.607

0.925

0.943

0.958

0.965

0.971

0.986

1.000

1.273

1.278

1.283

1.082

1.062

1.043

1.036

1.029

1.014

1.000

0.787

0.783

0.779

oCD

III

aQ' :::I

values calculated for 70 C temperatures by using the following temperature coefficients of resistance:

6063-T6 ................... . 0.00350

..................... 1100-HI8 ..................

55 EC

1100-0 .................... 0.00389

606l-T6 ................... . 0.00264

••••••

0

••••••••••••••

0.00363

57 EC

..................... ........................

0.00376 0.00376

56 EC .................... . 0.00370

59 EC

0.00389

6063-T83

EC

0.00403

•••

0

•••••••••••••••

0.00370

alternating current rating. This is true where the skin effect resistance ratio of the two materials investigated is veIY low or nearly the same and where proximity can be ignored. Where a more accurate equivalent alternating current rating is desired, the d-c rating obtained by the conversion factors in the table must be corrected to allow for the difference in the skin effect resistance ratios of the two conductors. For the standard shapes, the a-c resistance can be determined easily by obtaining first the d-c resistance value at 70 C for each conductor and then multiplying this value by the respective skin effect resistance ratio for each conductor as obtained from the following curves: 1. Round conductors-solid or tubular, page 25; 2. Square conductors-solid or tubular, page 26; '·3. Rectangular conductors, page 24.

Copper- 98 per cent conductivity ......... 0.00385 Copper- 99 per cent conductivity ..... , ... 0.00389 Copper-lOO per cent conductivity

1 -

2

IR2~c

'\j R lac •

....... 0.00393

Where: I 1 is the altemating current rating desired for conductor 1; R lac is the a-c resistance of conductor 1; I 2 is the known altemating current rating of conductor 2; R 2ac is the a-c resistance of conductor 2. The following example illustrates the calculation of the altemating current rating of a 55 EC rectangular bar having a conductivity of 55 per cent using the current ratings of an EC aluminum rectangular bar of the same shape but with a conductivity of 61 per cent. The equivalent values in Table 4 are used to simplify this conversion. These charaCteristics apply to a 3 X ¥4 inch EC aluminum bar with current ratings given for a vertical arrangement.

With these data, the altemating current rating, I 1 , can be determined by the following ratio: I - I

.

Material

Size (Inches)

EC Aluminum 3 X

¥4

Current CarryD-C Resistance ing Capacity ( Microhms at 70 C Per Foot) (Amperes) 20 C 70 C D-C 60 cps

17.81

21.40

780 760 47

_==Uf'


The conversion of the a-c rating of the above EC aluminum bar to the rating of a 55 EC rectangular bar of the same shape is given as follows. The d-c resistance at 70 C for 55 EC aluminum alloy bar, using the conversion factor 1.089 from the table is: R de70 = 21.40 X 1.089 = 23.30 microhms per foot at 70 C. To determine precisely the equivalent a-c values, the skin effect resistance ratios should be calculated and used to correct the d-c resistance values. The skin R effect resistance ratio, Rae, for a 3 X Y4 inch EC de

aluminmn bar is determined from the following calculated values and the curves on page 24.

/f

'\I

X

Rc/e7o

W

Rae de

/60,000 V 21.40

The skin effect resistance ratio,

R Rae,

for a 3 X ~

inch bar of 55 EC is obtained from the curves on page 24 after calculating these values:

dC70

/60,000 = 50.8

'\j 23.30

.

.

-R = 1.036 (from page 24).

jl

The a-c resistance at 70 C for 55 EC aluminum alloy will be: RaC70 = 23.30 X 1.036 = 24.14 microhms per foot. The equivalent alternating current rating of the 55 EC bar may be found from the formula below where R lae and R 2ae are the a-c resistances of the two bars:

"

11 =12

I'"

f_

"I

,

"

:. 1. , i'L~' ,J"

.i

I ' .I": • "

i

"'

I I,

J: j (/I

1':1 I,

1 1'1: 1 ,

I

1

, I"

'

;,

I

" "1 . ;11;'

~l':d'n,

= 1.084.

This compares with a skin effect resistance ratio of 1.041 for an EC aluminum bar of the same shape and 1.036 for a bar of 55 EC aluminum alloy. The d-c resistance of the copper bar using the conversion factor in the table for d-c resistance at 70 Cis: R de - cu = (0.618) (21.40) = 13.22 microhms per foot. R The a-c resistance, using the Rae ratio, will be:

= (13.22) (1.084) = 14.33 mierohms per

~

=

/2228 760V24:14

= (760)

/14.33

155

(0.961)

= lei< '\j 24.14 =leu X 0.771 for a-c conversion.

This compares with the direct current conversion factor of 0.753 as calculated below from values in the table: leu

lEO

lae

= 730 amperes.

The conversion factor for the alternating current rating is 0.961. This compares with the tabulated value of 0.958 for the conversion of the d-c rating. These factors are so nearly equal that for many applications, 48

The conversion factor applying to the 60 cps current rating of 55 EC will be calculated from its a-c resistance at 70 C, calculated above as R ae55 = 24.14 microhms per foot:

R2ae

-R

The a-c rating, then, of the 55 EC bar is:

I

74 6.

foot.

de

1. " , 1 ;,;

de

Rae-au

Rae

I

,I.

Rae

-R

/4

I"

=

de

W 3 -t =v=12

L' "

3

/60,000

'\j 13.22

The skin effect resistance ratio for the copper bar corresponding to the above is:

rle

10

103

W T= 12.

= 1.041 (from page 24).

/f X V R

X

V Rde20

.

The a-c resistance at 70 C for the EC aluminum bar is: R aC70 = 21.40 X 1.041 = 22.28 microhms per foot.

,

/f

= 529

3 ~ =12

T= -R

3

10 =

the d-c values could be used with sufficient accuracy where an approximate value for the alternating current rating is desired. When the change in the conductivity of the two bars is small, the difference in the a-c and d-c conversion factors will also be small. When the materials have a considerable difference in conductivity, skin effect will have a greater influence on the a-c resistance of the higher conductivity material. For example, assume a conversion factor is desired for converting the a-c rating of a copper bar with 98 per cent conductivity to the rating for a 55 EC aluminum bar with 55 per cent conductivity. For the size just calculated, the skin effect resistance ratio for an iden- , tical size copper bar can be obtained by using the curves on page 24 with the following values:

155

155

= 1.273

155

and lEO = 0.958 0.958 leu 1.273 = leu X 0.753 for d-c conversion.

=

Effect of Bus Enclosures Current ratings for indoor bus bar installations are based on a given temperature rise over ambient in

elect1'ical design - section II

still but unconfined air. These ratings apply to installations in a large enclosed room without circulating air, in which the volume of air is sufficient to prevent the heat generated by the bus from having an appreciable effect on the room temperature. Cooling is affected by natural convection air currents and by radiation. Where the bus bars are installed in an enclosure, the heat generated is also dissipated by radiation directly to the inside walls of the housing and by convection air currents. The small volume of air in the enclosure rapidly increases in temperature as it recirculates in this confined space. The temperature rise of this trapped air will depend upon tlle amount of heat it can transfer to the housing before it is recirculated. There exists, therefore, a series of temperature gradients in a bus enclosure, i.e., from the bus bars to the enclosed air, from the enclosed air to the walls of the enclosure, and from the walls of the enclosure to the surrounding air. This process of heat transfer from a small bus enclosure slows up the cooling process, and a de-rating factor is necessary to prevent tlle bus from exceeding its upper temperature limits. The magnitude of the de-rating required when a bus is enclosed in a nonmagnetic housing such as aluminum is variable and will depend on several factors, such as the size of the housing, the quantity of heat generated by the bus, and the relation between the radiation and convection heat losses of the conductor. High current, laminated, rectangular bus bars with Hat sides vertical are cooled principally by convection air currents and depend to a high degree on "chimney effect" for cooling, i.e., the updraft between laminations. Such arrangements will require a more drastic de-rating when installed in a confined housing since convection cooling represents a greater than normal avenue for heat dissipation. The current carrying capacity of enclosed buses in non-magnetic housings can only be discussed in general terms because of the variable factors noted above. De-rating factors for three phase bus arrangements in a compartmented 24 K,V. enclosure each 30Y2 X 32~ inches-have been presented. * For these conditions, the following approximate ratio applies:

Rating in Non-Magnetic Housing do . In or Current Ratmg

= 75 per cent.

A ratio of only 60 to 65 per cent applies for high current, laminated bus bars that depend upon convection air currents as the principal cooling medium. '" "Carrying Capacities of Enclosed Buses" by A. P. Fugal, ELECTRICAL WORLD, March 19, 1932.

Non-magnetic housings are preferred over magnetic housings for a-c bus bar enclosures, particularly for high current installations and installations where the bus is in close proximity to the walls of the enclosure. Alternating current induces eddy currents in the enclosure walls and, in magnetic material, causes additional hysteresis losses, both of which raise the temperature of the housing. Non-magnetic housings eliminate the losses due to hysteresis. Oftentimes a further de-rating is necessary where magnetic enclosures are used. * The relationship between the current ratings in these two types of housing was found to be approximately as follows:

Rating in Magnetic Enclosure 5 R' . N on- Magnetzc . E nclosure = 8 per cent. atmg m This percentage will valY depending upon the proximity of the conductor to the walls of the enclosure and tlle magnitude of the current in the conductor. Common practice is to limit bus bars carrying alternating currents to 1200 amperes when they are instaUed in a magnetic housing. For higher current ratings, a non-magnetic enclosure is usually required. A common enclosure for a three-phase bus installation, such as generator phase bus, usually requires a non-magnetic aluminum housing to minimize heating. In these common enclosures, the heat generated by the combined three-phase circulating currents induced in the covers of the enclosure limit the rating of enclosed bus. When current ratings are 6000 amperes and over, it is common practice to isolate each phase in an individual non-magnetic aluminum enClosure.

Effect of Painting Bus Bars Painting the surface of an aluminum bus bar is done to increase the amount of heat loss by radiation. New aluminum surfaces have a relatively low emissivity which is improved in time upon exposure to the atmosphere. Outdoor weathered bus bar having average tarnished surfaces is usually considered to have an emissivity of 0.5 and indoor bus to have a slightly lower value, taken generally as 0.35 for average conditions. This compares with the value of 1.00 for the ideal black body. For indoor applications, the current rating of a bus bar can be increased appreciably by painting it with a Hat, non-metallic paint of any color. Increases in current rating up to 25 per cent have been attained by the use of some types of Bat paint. A particularly effective application for painted bus bar is isolated phase bus.

MECHANICAL DESIGN SHORT CIRCUIT FORCES ON BUS CONDUCTORS

The mechanical design of bus conductors and their supports must include provisions for resisting the electromagnetic forces due to short circuit currents. These forces, which are exerted on the conductors during short circuit conditions, are in tum transmitted.') to the insulator supports. Bo~h conductors and su?) ports must be designed to wIthstand these short Cll'cuit forces in addition to the natural loading of the bus conductor. The lateral forces of attraction or repulsion exerted on bus conductors during short circuit produce several force components acting on the insulator supports. These are: Lateral forces exerted on these supports at right angles to the axis of the bus conductors; Longitudinal forces which deflect the insulator supports in the direction of the axis of the bus due to the greater bus deflection tending to pull the supports toward the center of the span; Torsional forces exerted on the insulator at the end supports when the bus swings laterally due to short circuit lateral forces.

Where: The currents i 1 and iz are the maximum direct currents or either (1) the instantaneous peak values of the altematmg current or (2) the maximum RMS asymmetrical alternating current; D is the separation between conductors in inches; k is the shape factor of the bus conductor. It is sometimes desirable to state this force in terms of absolute units for convenience in deriving equations for certam shapes of conductor, as:

F

2 k i iz = -D-(Dynes per centimeter of bus length). 1

A r : : L E Of TORSIONAL ROTATION

)(

TORSIONAL fORCE LONGITUDINAL FORCE

LATERAL fORCE

Such forces, Fig. 1, are illustrated in a typical outdoor bus installation.

Lateral Forces

,

,.,'I ,"

:

~~

it.

The direction of the lateral short circuit forces acting on two bus conductors will be one of repulsion when the currents in the two conductors are in opposite direction. When the currents are in the same direction in the two conductors, the force will be one of attraction. Such a condition exists, for example, in a bus conductor composed of two channels arranged in box form. The proximity of the two channels requires the addition of spacer clamps at short intervals along the conductor to maintain a separation during short circuits. These spacer clamps also add rigidity to lateral movement of the bus conductor. Calculation of this lateral short circuit force between conductors utilizes the basic short circuit formula. This formula gives the force between conductors in pounds per foot length of bus conductor: F

=

5.4 k i 1 i z 10-7 D

(Pounds per foot length).

Fig. 1 - Short Circuit Forces

Mter the solution has been obtained from this fundamental relation, the units of measure can be converted to the standard units of pounds and inches by simple conversion factors. *

* prised "Equatio;'s for the Inductance and ShRrt Circui~ Forces of Buses. C,?mof Double Channel Conductors, C. M. SIegel and T. J. Hlggms, AlEE Trans, Vol. 71, January, 1952, pp. 522-531.

!\ "

51

=

section III - mechanical design

Value of k-The value of k in the foregoing equations is determined from the physical shape and arrangement of the bus conductor. It is commonly referred to as the shape factor. For the common shapes of bus conductor, the value of k will be as follows:

( 1.75 or 1.8)

X

I EMS

RMS current (lst half cycle ); i"

2. Round tubular conductors and symmetrical square

tubular conductors for all practical purposes will have a value of k equal to unity. The value of k for non-symmetrical rectangular tubular conductors can be calculated.** However, for the practical spacings used for rectangular tubular conductor, the value of k can usually be taken as unity. 3. The equations for short circuit forces for double

channel and sb'uctural shapes of bus bar have been advanced by Siegel and Higgins and by Higgins. *** In these equations, forces are determined from fundamental formulas. Short Circuit Current-The short circuit current that will produce the maximum electromagnetic force is the maximum d-c fault current or the maximum peak instantaneous value of alternating current. For most design applications, the maximum value of the short circuit force is desired. However, to determine this force, peak currents often must be' calculated in terms of other current values. For example, the ratings of some equipment are based on the root mean square (RMS) symmetrical short circuit current values. To differentiate between the various currents, the symbols below are used to designate current values described in the following paragraphs. i' = instantaneous peak symmetrical current; ( I

I RMS = 'I,

i

z'1 ,

y2 symmetrical RMS current;

= instantaneous peak asymmetrical current (i = 2i/ );

* Fonnulas for the Geometric Mean Distances of Rectangular Areas ** ***

52

and of Line Segments," T. J. Higgins, JOURNAL OF APPLIED PHYSICS, April, 1943, Vol. 14. "Fonnulas for Calculating Short Circuit Stresses for Bus Supports for Rectangular Tubular Conductors," T. J. Higgins, ELECTRICAL ENGINEERING, August, 1942, Vol. 61, pp. 578-580. "Formulas for Calculating Short Circuit Forces Between Conductors of Structural Shape," T. J. Higgins, ELECTRICAL ENGINEERING, October, 1943, Vol. 62, pp. 659-663. "Equations for the Inductance and Short Circuit Forces of Buses Comprised of Double Channel Conductors," C. M. Siegel and T. J. Higgins, ELECTRICAL ENGINEERING, Oct., 1943, Vol. 62, pp. 659-663.

= average peak asymmetrical current, see page 60;

=1.25i'.

1. For rectangular bars the value of k may be deter-

mined by equations advanced by Higgins * from the bus bar dimensions and spacing. However, graphical solutions are more practical for the usual rectangular bus conductor applications and offer, in addition, a visual comparison of the values of k for different shapes and arrangements of rectangular bar. The value of k in terms of the ratio of conductor dimensions and spacing is shown in Fig. 2. It will be noted that where the long sides of the rectangular bars are perpendicular to the plane of the axes, k will be less than unity. If the short sides are perpendicular to the plane of axes, k will be greater than unity.

= maximum asymmetrical

Symmetrical Currents-When it is desirable to use the RMS values of current in calculating short circuit forces, a multiplying factor is necessary to correct RMS values to instantaneous peak current values in the formula. Symmetrical RMS values are denoted by the value of T in Fig. 3. Th~peak instantaneous symmetrical current, i', in terms of the symmetrical RMS current is:

i' =

y2 I EMS

and I EMS = 0.707 i' .

A symmetrical a-c short circuit current results when the fault is initiated at the instant of peak voltage. The current is symmetrical about its axis and no d-c transient exists for this short circuit condition. Instantaneous peak current is represented in Fig. 3 on page 54 by the crest value, B, of the symmetrical CUlTent.

Asymmetrical Currents-The condition for a symmetrical fault current is seldom attained in actual practice; an asymmetrical fault is the general rule since the probability of the fault being initiated at the instant of peak voltage is very small. When the fault is initiated at zero voltage, a maxinrum asymmetrical condition exists and the alternating current wave is fully offset from its axis. This gives a momentary peak current, i, in the first half cycle which decays rapidly as shown in the sketch, Fig. 3. This peak current reaches a value designated by point A, and represents the maximum possible fault condition. This maximum short circuit disturbance usually governs the design and selection of electrical equipment such as bus conductor and bus conductor supports. Normally, the severity of the fault CUlTent will range in magnitude between a symmetrical fault current and a maximum asymmetrical fault current, depending upon the point on the voltage wave in which the fault is initiated. For this reason, the maximum asymmetrical RMS current is sometimes used in place of maximum peak current particularly where dampmg is present in the system. This maximum asymmetrical current is composed of two parts: 1. A d-c decaying component;

2. A sustained a-c componE;nt. The diagram, Fig. 3, shows these current components for an asymmetrical fault condition.

mechanical design - section III

SHAPE FACTOR, k, FOR RECTANGULAR CONDUCTORS 1..4

1. 3 ' .

~~

I A-

~-O A B

I\.

\.

1. 2

I'.. I'\.

"- "......

"

......

1. 1~ ~A""""

5

r-...

r-....

r-.

r-.

I - 1-8=2

1t-

l-

'-""r- +-

f-

1.O

_A B

1-....

--

l...l...-

l-I--

-- --

I-

V

v

~A - .5, / L..-

~

t-t- +-

1

0.9 I-

t-

-

1--1-

I~--

--

.... _I_f.--

I...-

L..-

L..l-

I/

A

~I..

V 1/

00.7 8·=·25 J w :>

/

II 1/

f7 I-~

A--j

....

~.

0.6

1. SINGLE BARS PER PHASE I ....

1/

~

~

1.7

1/

r7

V"

L..-

I.....

O. 8

i 1/

i

0.5

/

I1-'1--''-1--

~I -I

1-11-1~I-

r-A-J

/

~~~ ~~~I

1/

J

II 1/

I-

·0.3 1-1- l - " 8 =0

I I

~

2. MULTIPLE BARS PER PHASE

1/ 0.4

f--

~S r-Tl

J

!-.~ =.1

rJ~ l-

s

l-

IS

-j

~s-'I

J / II

I

IT 0.1

-,.

1

I I

II

o 0.2

0.4

0.6

0.8

1.0

I I I I I I I I I I I I I I I I I Tl I I I I I II I I I 1.4 1.2

1-11-11-11-11-11-11-1-'II-~

1-1I-~

1-1I-~ I-~

1-11-11-11-11-11-11-11-11-11-1-

I I I I I I I I I I I I I I II I I

1.6

1.8

2.0

S-A A+B H. B. Dwight, "Electrical Coils and Conductors," McGraw-Hill Book Co.

Fig. 2

53

section III - mechanical design A

n:--Tl"~~Ir""""r-i:----"--~~_B --T

Fig. 3 - Short Circuit Current* I)

Where: AB is a curve passing through maxima peak cur-

II

'Ii I

'j

,

-I

L ~ j'

_il i: )1 . :,1 T.- ;:',';,

rent values; EF is a curve passing through minima peak current values; DC is the d-c component midway between curves AB and EF and represents the offset of the a-c current due to the d-c component; ST is a curve of the RMS values of the alternating current component only; RT is a curve of the RMS values of the alternating and direct currents. The theoretical maximum asymmetrical peak current as shown by the value at A on curve AB will be a maximum in the first one-half cycle. For conservative bus design, this value will be used to determine the maximum electromagnetic force produced by an asymmetrical short circuit. This maximum instantaneous peak asymmetrical value of current, i, as represented by the conditions in the first one-half cycle will be twice the normal symmetrical peak current, i = 2i', and in terms of the symmetrical RMS current as represented by the value, T, on the curve, ST, it becomes:

,I, .'

i = 2i'

>11[,J_

= 2 (y2I

RMs )

= 2.828 [RbiS Maximum peak asymmetrical

, ,1

amperes.

Effective Current-It is sometimes desirable to use the effective value of current rather than maximum peak current in the calculation of electromagnetic forces. This effective value of current is represented by the curve, RT, and its value at any instant is the

* A.

G. Darling, "Short-Circuit Calculating Procedure for Low-Voltage A-C Systems," AlEE Transactions, 1941. Vol. 60.

54

square root of the sum of the squares of the RMS value of alternating current represented by the curve, ST, and the instantaneous direct current represented by curve, DC. The maximum asymmetrical RMS value of the total short circuit current is represented by the value, R, on the curve, RT, and is sometimes taken as 1.75 or 1.8 times the value of the RMS symmetrical current value. Where these values of current are used to determine short circuit forces, it is well to investigate the system for possible vibration resonance and determine the proper stress factor to apply to the ' system, page 59.

:,i

.,

.

'.i

NEMA Standards The National Electrical Manufacturers Association ( NEMA) standards for Power Switching Equipment, Publication No. SG6-1954, has established conservative standards for the calculation of electromagnetic forces between two current carrying conductors. The basis of this calculation is the fundamental formula for short circuit forces using instantaneous peak current values to establish the maximum force. This standard recognizes the fact that the forces thus calculated are, in most cases, higher than those that actually occur. This, however, tends to compensate for the possibility of increased force due to resonant vibration since this factor is not taken into consideration. The standard force formula shown gives the force in pounds per foot of conductor:

F=M

5.4 i 2 X 10-7

D

The value of i in this formula is taken as maximum asymmetrical peak current and is used in conjunction with a multiplier, M. When maximum peak current is substituted, M 1 for a d-c fault or a single-phase

=

~

;

.'.\

'1 'j


fault on either a single-phase or a three-phase circuit. Often it is desirable to use RMS current values either symmetrical or asymmetrical. Where these current values are available, they can be used in the formula with a corresponding value of M from the following table. The multiplier, M, acts not only as a correction for peak current but also corrects for the maximum force in a' three-phase fault, taken as 0.866 the value of a single-phase fault. This maximum force occurs on the center conductor of a flat symmetrically spaced arrangement, page 57. MULTIPLYING FACTORS Current Used

Circuit

Multiplying Factor, M

Current

1.00

1.0

1 phase a-c or Maximum peak 1.00 1 phase of 3 phase

1.0

Maximum peak

d-c

1 phase a-c or 1 phase of RMS asymmetrical 3 phase

1.63

(1.63)2 or

2.66

1 phase a-c or 1 phase of RMS 3 phase' symmetrical

2.82

(2.82)2 or

8.0

0.866 X (l)2

0.866

** 3 phase a-c ** 3 phase a-c

3 phase a-c

**

Maximum peak 1.00

, RMS asymmetrical

I 1.63

0.866 X (1.63)2

2.3

2.82

0.866 X (2.82)2

6.9

RMS symmetrical

r.;.

Relation to Peak

*

* NEMA "Standard for Power Switching Equipment," 1954. ** For the center bus of a flat symmetrically spaced bus.

Publication SG6-

Calculation of Fault Current

,. '.,

The calculation of actual short circuit current usually involves the use of symmetrical components, except where the three-phase short circuit is considered. For high voltage installations where resistance is small compared to reactance, the circuit resistance can usually be neglected and calculations based on reactance values alone. On low voltage installations, this is not always true, but in cases where circuits are comprised of h'ansformers, generators, and reactors, the value of reactance may be sufficiently greater than the resistance so that the reactance alone may be used without introducing too great an error.t An investigation of the relative magnitudes of resistance and reactance in a circuit will reveal whether reactance values alone can be used or whether a more accurate det61mination is advisable, using impedance values. In determining the total impedance on low t "Calculation of Fault Currents

voltage circuits, all small impedances become important and such components of circuit impedance as bus bars and their connections, disconnects, switches, and current transformers should all be considered in the total. Since the severity of the short circuit force on a bus conductor and its supports is dependent upon the magnitude of the fault current, the mechanical design of a bus installation should be based on a maximum fault condition. For most conditions, a three-phase fault may be used as an indication of maximum fault current for design purposes. This will be conservative for line to line faults in which the current magnitude is approximately 86 per cent of the three-phase value. For line to ground faults, the current may be greater or may be less than the three-phase fault current, depending upon the fault location in the circuit or the magnitude of the ground resistance. The three-phase fault current is of such a magnitude that it can often be used to represent line to ground fault conditions. Many bus installations connected to transformer secondaries are designed to withstand the maximum fault current output of the three-phase transformer bank. The calculation of this fault current is based on sustained primary voltage and the amount of power on the primary side. The formula for the greatest symmetrical three-phase short circuit current on the secondary side is:

in Industrial Plants," Raymond C. R. Schulze, ELECTRICAL ENGINEERING, June, 1941,pp. 271-279.

Where: KVA

X 100 =KVAy3X X1000 amperes. E XZ

= rating of three-phase transformer or trans-

former bank; E = secondary voltage of h'ansfOlmer or transformer bank; Z = per cent impedance of transformer or transformer bank. For example, assume a three-phase transformer bank with a capacity of 45,000 KVA. The voltage of the bank is 66,000/13,200 volts and the per cent impedance of the transformer bank is 10 per cent. The maximum three-phase secondalY short circuit current is· desired assuming sustained primary voltage and capacity available on the primary side.

KVA = 45,000 Secondary Voltage, E = 13,200 volts Per cent impedance of bank, Z 10 per cent

=

I = KVA X 1000 X 100 \/3 X Ex Z 45,000 X 1000 X 100 - 1.732 X 13,200 X 10

= 19,700 RMS amperes (three-phase symmetrical short circuit current).

55

=


The vector sum of the two forces will vary in magnitude depending upon the angular displacement of the short circuit currents from the reference axis. A plot of the cosine functions through 180 electrical degrees will give one complete cycle of the functions. This is shown in Fig. 5. The total force, F A, which is the vector sum of the individual forces on bar, A, is equal to their numerical sum in this case since the forces are in the same direction. This total force becomes:

Calculation of Lateral Short Circuit Forces Force Between Two Conductors-The calculation of the electromagnetic short circuit force between two conductors involves the substitution of the proper values for the shape factor, k; the separation, D, in inches; and the short circuit currents, i 1 and i z, in the formula on page 5l. Where more than two conductors are involved, the short circuit force on anyone of the conductors is the vector sum of the forces between this conductor and each of the other conductors comprising the circuit. Force on End Conductor of Three-Phase Bus Spaced Horizontally-The total three-phase short circuit force on the end bar of a three-phase bus arranged with a horizontal symmetrical spacing of D inches as shown in Fig. 4 would be as follows. Using the vector relationship indicated for the three-phase symmetrical short circuit currents, equations can be written for the forces between any two bars. The total force on the outside bar, A, will be the vector sum of the forces between bars A and Band between A and C. These forces are:

z

F.!

AS

= F. w

5.4 k iAiB X 10D 54 k X 10-7

= . 2D = 5.4 k iAie X D

(

~

( iA COS a i e COS

,,, ,• ••

o -% ::l c..

-Y2

'"

Q)

cos a cos f3

+ cos a2cos OJ

«

0 in

cos a COS fJ

[

z o

w

7

X

;:: u

z

54 k X 10-7 F,IB=' D (iAcosaiBcosp)

7

= F + F,1O = 5.4 ki DX 10-

-%

,.

"

"

'.

~

v·- "-._,

,'Aoo /o%~ "

#

",,

1500-~

120"

\

\\ ,,

"1--..., ~./

,

'.

" 1

V

1\

\\

, ,• . .. '

,,

MAX: AT 165' (.0;768)

(J )

-1

10-7 ( cos a cos (J ) 2'

.-~.-

•••.• cos.I. cos,9

- - _ y, COsrJ..

COS I)

- - - VECTOR SUM OF COSINE FUNCTIONS

o[ oB

oC

"!II, 1 I

:I

REFERENCE

'f

!

Fig. 5 - Value of Cosine Functions

The sum of the cosine functions in this formula is a maximmn at 165 degrees, with a value of 0.768 as graphically shown. For a symmetrical three-phase fault, where i A is ie, the maximum force on the outside conductor of a symmetrical flat arrangement with a spacing of D inches will be 0.768 times the value for a single-phase fault of the same magnitude. The formula, then, for the force on the outside conductor of three symmetrically spaced conductors in a flat arrangement for a three-phase fault is:

= =

FA

(0.768) (5.4) ki z X 10-7 D

=

(lbs. per foot of conductor).

Fig. 4

56

.'1 1

Force on Center Conductor of a Three-Phase Bus with Flat Symmetrical Arrangement-The force on the center conductor of the same three-phase symmetrical flat arrangement of bus conductors will be the vector sum of the forces F I3A and F 130 which are given by the equations:

::l


54 k X 10-1 F BA = ' D ( iB 7

= 5.4 kiniD X 10A

F no

=

5.4 k

X

D

f3 iA

COS

10-1

(i B

(

X

COS

symmetrically spaced conductors in a flat arrangement for a three-phase symmetricalfault will be:

(l')

cos f3 cos (l'

)

FB

= (0.866) 5.4D ki

'1 (

cos f3 cos

8)

2

z o

;::

u

-< ......'"

Yz

/

-
t__t--___l

)

FORC,ES ON B 1 5.4 k 10-1

1i

)

cos a

k 10-1 ,(. F AIA2 = 5.4 3D ~Al cos a 5.4 k 10-1 • 4D (ZAI

'i

cos (3 i A2

COS

a)

(i BI cos (3 iB2 cos (3)

54 k 10-1 . 4D (iBl cos

/3

i 02 cos ()

0°

30°

60°

90°

120°150°

180°

Fig. 8 - Vector Sum of Cosine Functions

The total vector sum of the forces on bars AI, B l , and C1 will vary with the angular values of the cosine functions. This total will vary sinusoidally as shown in Fig. 8, which gives the vector summation of these cosine functions for 180 electrical degrees. A maximum value occurs for each bar as follows. On: Bar Al at 162 degrees-vector sum 0.72 (maximum value); Bar Bl at 76 degrees-vector sum 0.78 (maximum value); Bar Cl at 95 degrees-vector sum 0.63 (maximum value).

j :j


The equations for the maximum total force on these bars for a three-phase symmetrical fault current with the bars arranged as in Fig. 7, assuming currents divide equally between the bars of each phase, will be: F Al =

(0.72) 5.4 ki 2 D

= (0.78) 5.4Dki

2

FBI

= (0.63) 5.4Dki

2

F 01

X

10-7

X

10-7

X

10-7

(1bs. perfoot on A,). (lbs. per foot on BI)' (1bs. per foot on CI)'

Vibration and Resonance Vibration in a system of bus bars subjected to a-c short circuit currents may be attributed to the frequency of the components of current resulting from the short circuit. The system frequency contributes the fundamental frequency to which the bus bars are subjected. The first harmonic of the fundamental frequency may also be present as a result of the combination of two sine waves of double fundamental frequency as was noted for a three-phase fault shown in the graphs on page 58. For asymmetrical faults, a doc uni-directional component of force is also present. This is a variable force with a rate of decay depending upon its decrement factor. A bus conductor ipstallation will have a natural period of vibration depending upon the span length, rigidity of supports, degree of damping, and elasticity of its members. The conductor supports will also have a natural period of vibration. The frequency or frequencies at which this assembly vibrates is a combi~ nation of the natural frequency of the conductors to which the force is applied and the supports which provide the reaction to such motion. The calculation

of this period of vibration has been advanced by several authors. * The conditions for vibration are increased by the proximity of the conductors, short span lengths between supports, the inflexibility of the supports, and the rigidity of bus bar members. Resonance may be established. when the conductors and their supports vibrate in harmony with the electromagnetic short circuit forces. The conditions for resonant vibration are most favorable when the natural period of vibration of the conductor and its supports is equal to, or nearly equal to, the fundamental frequency or double fundamental frequency. This resonance may produce a significant increase in the normal short circuit stresses in a bus bar. In some cases, stresses may be many times greater than normal and it is desirable to change the natural period of vibration of the system by varying design conditions. Such variations as the following are effective in changing the frequency of vibration: Increase span lengths between supports to reduce natural frequencies; Provide flexible SUPPOlts so that more of the initial energy will be absorbed in the movement of the conductor and supports. In installations where bus bars are designed to swing laterally with the short circuit forces, extremely large short circuit currents can be encountered with little or no damage; The flexibility of a conductor will affect its natural period of vibration. Greater flexibility will decrease its natural period of vibration.

Stress Factors (p)-Where a bus bar system vibrates at or near a resonant frequency, it is sometimes necessary to assess a stress factor which, when multiplied by the force as calculated from the standard short circuit formula, gives the approximate increased force, P, due to resonance. It is: P

= P X F (lbs. per support).

Where: p is the stress factor; F is the force as calculated from the electromagnetic force formula for the span adjacent to the support. For doc short circuits, the initial force is suddenly applied to the supports with an impact that gives a higher initial force than the sustained short circuit force. The stress factor for this condition would theoretically be two. Actual determinations of these impact forces may show this stress factor to be slightly in excess of two or somewhat less than two, depending upon how much inherent damping is present in the system.

* "Short-Cut Method of Calculating Stresses in Bus Conductors," W. Specht, Flexible Supports ReduceVibriiffon

GENERAL ELECTRIC REVJEW, Vol. 31, No.8, August, 1928. "Sb-esses in Bus Supports," R. Tanberg, THE ELECTRICAL JOURNAL, Vol. 24, No. 10, October, 1927, pp_ 517-525. "Mechanical Stresses in Bus Bar Supports During Short Circuits," O. R. Schurig and M. F. Sayre, ALEE Trans., Vol. 60, pp. 478-486, Apr., 1925.

59


For the usual outdoor installations of bus bar, under 66 KV, flexibility is inherent due to the long spans. This usually provides enough damping so that the initial movement of the conductor and its supports absorbs a part of the initial energy, A stress factor of one can usually be taken for these installations. On higher voltages (66 KV and up), considerable damping is usually present due to the length and flexibility of the bus and the height of the insulator stack. Short circuit forces calculated by the accepted methods outlined may be more conservative than is required since the natural frequencies of the bus assembly may be so low that allowances for resonant vibration are unnecessary. Where such a condition exists, a more realistic substitution of average asymmetrical peak current rather than the maximum asymmetrical peak current may give forces which are closer to actual effective values. Tests on long span high voltage conductors show that short circuit force calculated by standard methods is very conservative. * The effective force that deflects the insulator and causes insulator failure is in close agreement with the force calculated by the accepted formula using the average asymmetrical peak current instead of the maximum asymmetrical peak value, It is assumed that the initial electromagnetic forces acting on a long tubular bus act as a series of successive forces which are used initially to bend and deflect the bus and to initiate movement of the insulators from rest. The initial peak current in the first half' cycle of an asymmetrical fault is, therefore, not fully effective in this case because of its short duration and the inherent damping in the system. Such force is approximated if the average peak current of an asymmetrical fault from inception to steady state is used in the fundamental force formula. This may be taken as 1.25 times the symmetrical peak current or in terms of symmetrical RMS current, it will be: iff = 1.25 X

y2 X I RMs

= 1.77IRMs • Where:

I RMs is the symmetrical RMS current.

I

i~,

This value substituted in the standard force formula will give the "effective force" on the insulators and bus in a high voltage long span tubular bus installation. The use of average peak asymmetrical current instead of maximum peak asymmetrical current gives a factor of 1.77 times symmetrical RMS current. This value is in close agreement with the factors applied to symmetrical RMS current values (1.75 to 1.8) to obtain the maximum asymmetrical RMS value of the total current, see page 54. " "Behavior of High Voltage Buses and Insulators During Short Circuits," R. M. Milton and Fred Chambers, AlEE Trans. 55-11, February 16, 1955.

60

Longitudinal Forces The lateral deflection of a bus conductor and its supports during short circuit conditions creates an accompanying longitudinal deflection of the bus supports. The greater the lateral deflection of the bus, the greater will be this force tending to pull the insulator supports together. This longitudinal force will vary from a minimum at the center of the bus system to a maximum at the end support. The design of the bus installation, then, should consider the magnitude of these longitudinal forces on the end support and the support next to the end where they are the grtlatest. The calculation of longitudinal forces is beyond the scope of this manual, but methods have been advanced by several authors to determine mathematically its value. * AXIS OF CONDUCTOR

_1_

2F

SUPPORTNEXT TO END

R2

= V (2F)2 + P22

Fig, 9

Although the longitudinal force, P, is less on the span next to the end, the lateral force, F, is approximately twice that of the end support for equal spans, The resultant force, then, will be greatest on the support next to the end unless there is considerable flexibility in the bus conductor. This is shown in Fig. 9. The maximum total cantilever force exerted on the insulator is the vector sum of the lateral and longitudinal forces and is calculated as R 1 and R 2 for the end span and the span next to the end, respectively. To reduce the longitudinal forces in a bus installation, several design factors may be considered. They are as follows: Increase the stiffness of the bus conductor in the direction of the lateral forces; Decrease the length of the span between supports; Decrease the number of continuous spans. The first two factors limit the lateral deflection of the bus and the third reduces the magnitude of the longitudinal force at the end support. For rectangular bar and structural shapes, the arrangement of conductors with their axis of greatest stiffness perpendicular to the direction of short circuit force will limit deflection

* "Stresses

in Bus Supports," R. Tanberg, THE ELECTRIC JOURNAL, Vol. 14, No. 10, pp. 517-525. "Short-Cut Methods of Calculating Stresses in Bus Structures," W. Specht, GENERAL ELECTRIC REVIEW, Vol. 31, No.8, August, 1928, pp. 413-418. "Practical Calculation of Short-Circuit Stresses in Supports for Straight, Parallel Bar Conductors," 0, R. Schurig and C. W. Frick, GENERAL ELECTRIC REVIEW, Vol. 29, No.8, August, 1926, pp. 534-544.


and, thereby, reduce the longitudinal force. Increasing the stiffness of the bar and decreasing span lengths will also change the natural frequency of vibration of the bus conductor and its supports. Where these factors increase the possibility of resonant vibration, a condition more serious may result because resonant vibration may increase lateral force to a far greater degree than they reduce the longitudinal force.

Torsional Forces Torsional forces are encountered in the end supports of a bus conductor installation. These forces are due to the twisting of the insulator support by the lateral swing of the bus bar during short circuit and

may be of serious proportions where the conductors are extremely flexible, and the late)'al movement is great. Since torsional stresses are a function of the lateral movement of the bus, they may be reduced by increasing the bus rigidity to lateral movement or by making the end support relatively free to rotate within limits. A slip fit support may also aid by allowing the bus to rotate slightiy within the retaining clamp. Where it is necessary to weld the bus in tile span, it is wise to reinforce the weld so that bending does not accompany the lateral movement of tile bus and tilereby increase the torsional force. Welds should not be placed in the center section of the bus where bending moments are high and may result in greater lateral deflections and permanent set.

BUS DESIGN Bus supports are designed for a cantilever sh'ess which is measured in inch-pounds, one inch from the base of the support. The total force acting on tilis support is the combined effect of the lateral and longitudinal forces imposed by electromagnetic short circuit conditions. In systems where considerable damping is inherent or short circuit forces relatively light, a small safety factor may be included in the design for these supports. Increased safety factors should be included where tile magnitude of tillS total stress is high and conservative design is anticipated. In outdoor installations, provisions should be made for the complete drainage of water that may collect on or within tile bus conductor shape. On a tubular bus, a small drainage hole in mid-span on the bottom will drain tile conductor. Such shapes as channel and I-beam sections should be arranged so that they drain naturally and do not allow water to stand in any depression. This water not only causes an increase in the dead load of the conductor but may initiate corrosion of tile conductor. Wind induced vibration in long span tubular conductors has been experienced in isolated cases under certain conditions. In most cases resonant vibration can be eliminated by threading a length of aluminum or ACSR conductor into the tube where it lays loosely and acts as a damper. This simple, effective method of dealing with wind induced vibration has become standard practice in tubular installations because of its simplicity and ease of installation.

Clearances Minimum standard clearances have been established between live parts of bus conductors such as switchboard circuits and other applications of rigid bus conductors. Tables 1, 2, 3 and 4 indicate acceptable clearances for various applications. The spacing of out-

door buses is based on design experience and physical size of equipment, and will vary with the voltage and application.

TABLE I-STANDARD FOR

SWITCHBOARD SPACING * Minimum Spacing in Inches Between Live Parts of Opposite Polarity

Voltage Involved

Minimum Spacing in Inches Through Air and Over Surface Between Live Metal Parts and Grounded Metal Parts

Over Through Surface Air

~

125 or less 126 to 250 251 to 600

2

* Underwriters'

Laboratories "Standard for Dead Front Switch-

%

1~

~

~

::Sl /4

1

1

boards."

i

TABLE 2 - MINIMUM CLEARANCES FOR SWITCHBOARDS* ~~'~~~:~eo~js~~~es~~~~e

Striking Distances when

Ri~?~rrS~rS~~I~~e:nd

of Insulating Panels

Between

Part~

of 0EPosite Po arity

% ~

%

1 114 1% 2Y2 3

Between Live Parts and Ground

~~

% ~

%

1~

1% 2Y2 3

Between Parts

of 0r-posite Po arity

Voltage Class**

Up to 50 125 250 600 750 1,500 2,500 3,500

Between Live Parts and Ground

~

:yg

~

%

% % %

1112

2 2Y2

~ ~

%

1~

!:(

2

;. ·1,.'

2~

i ; ;:

*Westinghouse Switchboard Data Book. **For intermediate voltages, it is advisable to use the distances given for the next higher voltage class. Note: For switchboard circuits connected to systems above 150 kva capacity, the distances between parts of opposite polarity should be increased from lh to 1 inch.

I'III !

i .J

61 "

r ,

.1

iL \

j"

-


TABLE 3 -MINIMUM CLEARANCE IN INCHES BETWEEN LIVE PARTS OR BARE CONDUCTORS IN AIR*

Deflection of Bus Conductors Bare and Loaded In designing, the deflection of a bus between its SUppOltS should be considered for both the bare or unloaded condition and for ice and wind loads added to its dead load. It should have a small unloaded or bare deflection so that it visually appears to be reasonably straight;

The bus, when subjected to ice and wind loads, should not be stressed above safe limits nor should it sag excessively.

The unloaded deflection is important from an appearance standpoint. A visible amount of sag in a bare conductor would present an unsightly appearance. The same bus, when loaded with ice, would not present an objectionable appearance because of a slightly greater deflection. It is often desirable in designing . long span buses to formulate a rule which will govern the maximum tolerable unloaded deflection of the bus. This rule, e,g., can be a constant ratio expressing the relation of deflection to span length or it can be a rule which establishes maximum deflection as a function of bus diameter or physical size. The maximum bare deflection of a long span tubular bus is limited by some designers to one diameter of the bus while others prefer to designate the maximum unloaded deflection as a certain fraction of the span length. Conservative design limits the dead load deflection to 1/150 or 1/200 of the span length, while less conservative design to 1/80 of the span length. To gain a straight or level appearance, bus con-

TABLE 4 -

Indoors Phase to Phase

Outdoors

To Ground

3Yz

2Yz

4 7

5Yz

3%

'1' ,I Of

J

I

I

d

!

;:

1

6 6 6 12

6 6 6 9

8Yz 12 16

25,000 37,000 50,000

17 24 32

13 18 23

30 36 45

23 28 34

73,000 88,000 110,000

44 52 64

,32

54 63

41 47

132,000 154,000

77 89

56 65

76 89

57 67

187,000 220,000

106 124

78 90

,

if It I",- . g.

n I.'

q

38 47

* Westinghouse Switchboard Data Book. ** For intermediate voltages, use distances

given for next higher voltage. Note: The above table is for rigid conductors only when supported clear of surface. For flexible conductors, increase clearances given by twice the maximum sag. Smaller spacings may be used for standard apparatus when all parts are shaped to minimize electrostatic stresses.

ductors are sometimes formed with a slight bow equal to the normal unloaded deflection. When this bus it>

STANDARD CLEARANCES AND PHASE SPACINGS* Centerline Spacing 2 Inch Rod Gap, 60-Cycle Dry (Inches)

Minimum Safe Clearance to Ground (Inches)

Hook and Gang Disk Switches and Bus Supports (Inches)

Nominal System Voltage

Apparatus Voltage Rating

Dry

Wet

6,900 13,200 22,000

7,200 14,400 23,000

60 85 110

40 55 75

4.2 7.6 10.7

6.0 8.0 11.0

18 24 30

36 36 48

33,000 44,000 66,000

34,500 46,000 69,000

145 170 235

100 125 180

14.1 16.9 23.7

14.0 17.5 24.0

36 48 60

60 84

110,000 132,000 154,000 220,000

115,000 138,000 161,000 230,000

385

285

39.5

84

120

485 660

380 560

50.1 68.6

39.0 45.0 51.0 71.0

108 156

168 216

* Standard

i .1

To Ground

11 16 21

E~uivalent

i

Phase to Phase

Up to 3,500 4,500 7,500 15,000

Insulator 60-Cycle Flashovers (Kilovolts)

:i

**

Voltage Class

Horn-Gap Switches (Inches)

72

clearances and phase spacings as adopted by the NEMA and based on the joint EEl - NEMA preferred system voltage and also using AlEE standards as a basis. Standard Handbook for Electrical Engineers.

62


then installed with the bow upward, the bare deflection neutralizes the upward bow and the bus conductor is straight or level between supports. The unloaded deflection is not usually the governing factor in a bus installation, particularly where heavy ice formations are encountered and high wind velocities add to the load imposed on the bus. These loads, along with shOlt circuit forces, add to the stress in the outer fibres of the bus conductor and should be limited to values that provide an adequate factor of safety. For most applications, it is satisfactOly to base the maximum fibre stress on a certain percentage of the yield strength or by reducing the yield strength by a £Xed amount. For the bus materials commonly used, the following yield sh'engths and suggested working stresses may be used as a guide in bus design. DESIGN STRESSES

,

Bus Material

EC-H17 EC-H13 55EC 56EC 57EC 59EC' 6063-T6 6063-T83 6061-T6 Drawn Copper Iron Pipe

Yield Strength (psi)

Thickness (Inches)

Up to Vz Up to % Up to Vz Up to Vz Upto%

Suggested Working Stress ( psi)

15,000 12,000 25,000 22,000 15,000 8,000 25,000 30,000 35,000 28,000

Up to Vz 0.050-0.150

10,000 8,000 15,000 13,000· 10,000 6,000 15,000 20,000 25,000 18,000 24,000

Ice Loading-Ice loads are assumed to be of uniform radial thickness on tubular conductors and of uniform thickness on all exterior smfaces of bus conductors such as channel or angle arrangements in box form. A factor of 57 pounds per cubic foot is commonly used to determine ice weight. Typical examples of ice loading are shown for channel bus and tubular or solid round bus.

r1 F

Tf:::::::':':::':':::::::::::::::::'::::

I 1:;: ; N +

...;}

ll", 2

(A

[(A

F X t = cross sectional area of ice on two flanges of one channel;

+ 2t) t =

cross sectional area of ice on outside web of one channel;

+ 2t) t + 2 Pt] = cross sectional area of ice on one channel;

2 [(A

+ 2t) t + 2 Ft]

X

12

= cubic inches of ice on two channels per foot of length;

Bus Loading-Ice and Wind Bus loadings are usually calculated for a given set of conditions depending upon geographic location and experience with ice and wind conditions. These must mst be determined before bus loads are calculated. Tables, pages 128-131, give bus deflections and stresses for bare or unloaded tubular bus conductors and for loadings of Vz inch ice, liz inch ice with 8 pounds of wind, and for 1 inch of ice. t

weight of ice = 1.244 t (D

X

::.:.:.:.:.:.:.:.:.:.:.:.:.:.:.'.'.:.:.

+ t)

lbsJft.

0.792 t [A

+ 2t + 2F] = weight of ice in lbs/ft on two channels.

Wind Loads-Wind loads are calculated for an assumed crosswind velocity acting on the projected area of the bus conductor. The projected area of an iced conductor is the over-all velucal dimension which includes the height of the conductor plus the top and bottom thickness of ice. The relationship between wind pressure in pounds per square foot of projected area and the actual wind velocity in miles per hour is shown in Fig. 10. The wind pressure on a cylindrical surface such as a tubular conductor will vary slightly from that on a flat surface such as a channel bus. This difference is shown by the two curves in Fig. 10 representing both types of bus conductors. The mathematical relationship for wind pressure and actual wind velocity is given by the following formulas:

63

:j

.," "


WIND PRESSURE VS. WIND VELOCITY I

I

60

I

I I II

55

I

IT J

I ,I

I II

50 I

I

I I

45

I I

I

J

I

I

t--=

I

I

'I

40

I

u..

II

V)

l:l::

w c..

I

J

d 35

II

J

II

vi a:l

I

-' W

l:l::

:::>

:B)

) = -WeB L - (max.ifB>A

I SHEA: DIAGRAM RlmTrm

I

I

= WC: X

M

W AB - _e_

1u...u...u...L.IIIIIIIIIIIIIIIIR2

-

IT

I

D

FS W

=2'

D

W.,(L-X) 2L

R 2

L

I -.L

l 2

WL

=8

M

~M

+ 2B)

V 3A (A 27 ElL

WeAB (A

"'a"

i

(if XM or M2 ,

= R1X -M1,

rrmm rutlllllllllllllllR2

G

= 1+2k

1M

H

I

W ema..

_~gl

.

,

I I

~"Oo414

2fS W",a" = kL (2 - 3k + k 3 )' 2fS W",ax = kL (1 _ k Z ),

D

D D ma"

if kOo414

_ WekV (1-k 2 )3 3 (3 - k 2 ) Z El ' W kV (k -1)2 e . 6El 0.0098 WeV El

if k""------')l

c=--s

BACKUP BAR OF EITHER ALUMINUM WATERCOOLED COPPER OR STEEL

".~ Fig. 19 - Tubular Joints

erally not necessary for metal-arc welding bus under

% inch. On sections thicker than % inch, a slight pre-

PLATE THICKNESS GREATER THAN ,/.'

------J(

C>

~

V:> V:>

*Current ratings are for a 30 C temperature rise over 40 C ambient temperature in still, but unconfined air. These ratings correspond to indoor current ratings with emissivity of conductor surfaces 0.35. **The following per cent (lACS) conductivities were used to determine re-

sistance and current ratings: EC-61 per cent; 57 EC-57 per cent; 6063-T6-53 per cent; 6061-T6--40 per cent. ***Width detennined by standard spacer support.

-;:l;

§.

o' ~ I

'"'""'" C>

o'

;:l

~ ......

f-'

~~ g ;:5

W

>I>-

I

Er (3""

f

~

ALUMINUM ANGLE BUS CONDUCTORS (Physical Characteristics of Single Angle Sections) Weight j,er oot (Lbs.)

Section Area (Inches) 2

2%x2 2%x 2

1.26 1.83

1.07 1.55

2%x2% 2lhx2%

1.40 2.05

1.19 1.74

3 3 3

x3 x3 x3

1.68 2.47 3.23

1.43 2.10 2.74

4 4 4 4

x3 x3 x3 x3

1.99 2.93 3.83 4.69

1.69 2.49 3.25 3.99

4 4 4 4

x4 x4 x4 x4

2.28 3.38 4.41 5.42

1.94 2.86 3.75 4.61

5 5 5

x3% x3% X 3%

3.58 4.70 5.79

3.05 4.00 4.92

4.24 5.58 6.88

3.60 4.74 5.85

6 x4 6 x4 6 x4

Thickness t (Inches)

1A % 1A % 1A % %

1A % %

% 1A % %

% % lh

% % lh

%

Section Modulus s (Inches)"

Radius of Gyration r (Inches)

Distance tox-x axis

:Jh :Jh :Jh % 1A 1A 1A 1A 1A 1A 1A 1A 1A 1A 1A

0.65 0.91

0.38 0.54

0.78 0.76

0.69 0.98

0.39 0.56

1.18 1.70 2.16

Radius of Gyration r (Inches)

Distance toy-;-y

(In!hes)

Section Modulus s (Inches)'

0.78 0.83

0.37 0.51

0.25 0.36

0.58 0.57

0.53 0.58

0.76 0.75

0.71 0.76

0.69 0.98

0.39 0.56

0.76 0.75

0.71 0.76

0.54 0.80 1.04

0.91 0.90 0.89

0.82 0.87 0.92

1.18 1.70 2.16

0.54 0.80 1.04

0.91 0.90 0.89

0.82 0.87 0.92

2.613 3.88 4.96 5.95

0.96 1.42 1.85 2.25

1.26 1.25 1.24 1.22

1.21 1.26 1.31 1.36

1.29 1.86 2.36 2.82

0.56 0.83 1.08 1.32

0.87 0.86 0.85 0.84

0.72 0.77 0.82 0.86

2.94 4.26 5.46 6.56

1.00 1.48 1.93 2.36

1.23 1.22 1.21 1.19

1.07 1.12 1.17 1.22

2.94 4.26 5.46 6.56

1.00 1.48 1.93 2.36

1.23 1.22 1.21 1.19

1.07 1.12 1.17 1.22

l}16 l}16 l}16

7.56 9.77 11.82

2.21 2.90 3.56

1.58 1.56 1.55

1.58 1.63 1.68

3.04 3.91 4.70

1.15 1.50 1.84

1.00 0.99 0.98

0.84 0.89 0.94

% % %

13.02 16.95 20.63

3.17 4.19 5.17

1.90 1.89 1.88

1.90 1.96 2.01

4.63 6.01 7.27

1.50 1.98 2.44

1.13 1.13 1.11

0.91 0.97 1.02

1A

1A 1A 5;16 l}16 l}16 % % % % % % % % 'K6 'K6 'K6 1,6 % 1,6

§.

Moment of Inertia Iy-y (Inches)'

Corner Radius f2 (Inches)

1,4

C'>

Axis y-y

Moment of Inertia Ix-x (Inches)'

Inside Radius h (Inches)

---

'"

-;i;

Axisx-x

Angle Size Length of Legs (Inches)

Co

""tl

See page 2 for the physical characteristics of aluminum alloys for angle bus conductors.

axIS

x (Inches)

c' 1:;

COWl DOUBLE ALUMINUM ANGLE BUS CONDUCTORS (Electrical Characteristics) (Aluminum Alloys - EC, 57 EC, 6063·T6, 6061.T6) Angle Size

Donble Angle

Weight per foot (lbs.)

(Inches)

21hx 2 21hx 2

1.26 1.83

21h 2:lh

2lh X 2:lh 2lh X 2:lh

1.40 2.05

(Inches)

Deth

Width w (Inches)

Double Angle D-C Resistance (Microhms per foot) at 20 C

**

D-C Current Carrying Capacity (Amperes)

at70C

*

ID

60 Cycle A-C Current Carrying Capacity* (Amperes)

~.

EC

EC

57 EC

6063-T6

6061-T6

EC

57EC

3 3

6.238 4.306

7.495 5.174

7.933 5.476

8.439 5.826

10.77 7.438

2010 2420

1950 2350

2:lh 2:lh

3:lh 3:lh

5.609 3.836

6.739 4.609

7.132 4.878

7.588 5.189

9.687 6.625

2230 2700

6063-T6

6061-T6

EC

57EC

6063-T6

6061-T6

1890 2280

1680 2020

1980 2310

1920 2260

1870 2200

1670 1980

2170 2620

2100 2540

1860 2250

2190 2580

2140 2520

2070 2450

1850 2200

- - -- - - - - -

3 3 3

x3 x3 x3

1.68 2.47 3.23

3 3 3

4 4 4

4.668 3.179 2.436

5.609 3.820 2.927

5.936 4.043 3.098

6.315 4.301 3.296

8.063 5.491 4.208

2610 3160 3570

2540 3080 3490

2460 2980 3360

2180 2640 2980

2550 3000 3260

2490 2930 3200

2420 2850 3110

2160 2570 2810

4 4 4 4

x3 x3 x3 x3

1.99 2.93 3.83 4.69

4 4 4 4

4 4 4 4

3.950 2.681 2.054 1.673

04.746 3.221 2.468 2.010

5.023 3.409 2.612 2.127

5.344 3.627 2.779 2.263

6.822 4.630 3.548 2.889

2980 3620 4110 4550

2900 3520 4000 4420

2810 3410 3870 4290

2490 3020 3430 3790

2910 3420 3730 3840

2840 3340 3650 3780

2750 3250 3560 3720

2450 2950 3230 3400

4 4 4 4

x4 x4 x4 x4

2.28 3.38 4.41 5.42

4 4 4 4

5 5 5:tA, 5:tA,

3.441 2.334 1.780 1.448

4.134 2.804 2.139 1.740

4.375 2.968 2.264 1.842

4.655 3.157 2.408 1.959

5.943 4.031 3.075 2.501

3390 4110 4710 5220

3290 4000 4580 5070

3190 3870 4440 4920

2830 3430 3930 4350

3290 3850 4230 4380

3210 3760 4160 4320

3120 3660 4070 4260

2790 3310 3690 3900

5 5 5

x31h X 3:lh X 3:lh

3.58 4.70 5.79

5 5 5

5 5 5

1.880 1.669 1.357

2.259 2.005 1.630

2.391 2.122 1.725

2.543 2.257 1.835

3.247 2.882 2.343

4340 4960 5490

4220 4830 5340

4090 4670 5170

3620 4140 4580

4090 4460 4640

3990 4380 4560

3890 4270 4480

3500 3870 4110

6 6 6

x4 x4 x4

4.24 5.58 6.88

6 6 6

6 6 6

1.854 1.408 1.141

2.228 1.692 1.371

2.358 1.791 1.451

2.509 1.905 1.544

3.203 2.432 1.971

5060 5790 6420

4910 5620 6240

4770 5460 6050

4220 4830 5350

4740 5160 5390

4620 5070 5310

4510 4970 5220

4060 4490 4770

* Current

ratings are for a 30 C temperature rise over 40 C ambient temperature in still, but unconfined air with a phase spacing sufficient to produce negligible proximity effect.

** The

following per cent (lACS) conductivities were used to determine resistance and current ratings: EC - 61 per cent, 57 EO - 57 per cent, 6063-T6 - 53 per cent, 6061-T6 - 40 per cent.

.,.. I::l

C?'

~

g

t:l.. Co

"13

"" C"l

'~

~

o' ~ I

Co

""~ t; Cil.

o';::I

:s

section VI - tables and specifications

SQUARE ALUMINUM TUBULAR CONDUCTORS (Physical Properties) Square a (Inches)

Corner Radius r (Inches)

Wall Thickness t (Inches)

3 3 3

% 112

%

Perimeter (Inches)

Cross Sectional Area (Square Inches)

Weight per foot (Lbs.)

Moment of Inertia I (Inches)

Section Modulus S (Inches)

Radius of Gyration (Inches)

14 %

11.36 11.14 10.71

2.643 3.736 4.571

3.108 4.394 5.375

3.272 4.215 4.600

2.181 2.810 3.067

1.113 1.062 1.003

8.215 11.30 13.06

4.108 5.652 6.532

1.513 1.469 1.410

lf2

4 4 4

lf2 lf2

%

14 % lf2

15.14 15.14 14.71

3.589 5.236 6.571

4.221 6.158 7.728

5 5 5

% % %

14 % lf2

18.71 18.71 18.71

4.482 6.575 8.571

5.271 7.732 10.08

16.26 22.73 28.32

6.503 9.093 11.33

1.905 1.859 1.818

6 6 6

% % %

14 %

22.71 22.71 22.71

5.482 8.075 10.57

6.447 9.496 12.43

29.36 41.59 52.35

9.786 13.86 17.45

2.314 2.269 2.225

lf2

SQUARE ALUMINUM TUBULAR CONDUCTORS (Electrical Properties) Wall Tube ThickSquare ness t a (Inches) (Inches)

57 EC

EC

60 cps Current Rating (amperes)

*

at 20 C

at 70 C

at 20 C

at 70 C

EC

57 EC

EC

57 EC

3 3 3

% % lf2

5.051 3.573 2.921

6.069 4.293 3.510

5.407 3.825 3.126

6.424 4.544 3.714

6.312 4.722 4.176

6.683 4.955 4.384

1930 2210 .2310

1880 2170 2250

4 4 4

Y4 % lf2

3.720 2.550 2.032

4.470 3.064 2.441

3.982 2.729 2.175

4.731 3.242 2.584

4.692 3.431 3.002

4.969 3.600 3.127

2520 2950 3110

2450 2880 3040

5 5 5

% lf2

1~

2.979 2.030 1.558

3.579 2.439 1.872

3.188 2.173 1.667

3.787 2.582 1.980

3.794 2.782 2.357

4.017 2.919 2.457

3060 3580 3880

2980 3490 3810

6 6 6

Y4 % lf2

2.435 1.653 1.263

2.926 1.986 1.517

2.607 1.770 1.352

3.097 2.103 1.606

3.160 2.304 1.972

3.346 2.419 2.056

3640 4260 4600

3540 4170 4520

* 30 C rise over 40 C ambient temperature in still but unconfined air.

136

60 cps A-C Resistance at 70 C (Microhms per foot)

D-C Resistance (Microhms per foot)

tables and specifications - section VI

INDUCTIVE REACTANCE SPACING "FACTORS" Microhms per Foot (For 1 to 251 Inches Total Spacing) FREQUENCY - 60 cps INCHES

SPACING (Feet)

7

0

1

2

3

4

5

0 15.9 25.2

-57.1 1.8 16.9 25.9

-41.2 3.5 17.8 26.5

-31.9 5.1 18.6 27.1

-25.3 6.6 19.5 27.7

-20.1 8.0 20.3 28.2

4 5 6 7

31.9 37.0 41.2 44.7

32.3 37.4 41.5 45.0

32.8 37.7 41.8 45.3

33.3 38.1 42.1 45.5

33.7 38.5 42.4 45.8

34.1 38.8 42.7 46.0

34.6 39.2 43.0 46.3

35.0 39.5 43.3 46.6

35.4 39.9 43.6 46.8

35.8 40.2 43.9 47.1

36.2 40.5 44.2 47.3

36.6 40.9 44.4 47.5

8 9 10 11

47.8 50.5 52.9 55.1

48.0 50.7 53.1 55.3

48.3 50.9 53.3 55.5

48.5 51.1 53.5 55.6

48.7 51.3 53.7 55.8

49.0 51.5 53.9 56.0

49.2 51.7 54.0 56.1

49.4 51.9 54.2 56.3

49.6 52.1 54.4 56.5

49.9 52.3 54.6 56.6

50.1 52.5 54.8 56.8

50.3 52.7 54.9 57.0

12 13 14 15

57.1 59.0 60.7 62.2

57.3 59.1 60.8 62.4

57.4 59.2 60.9 62.5

57.6 59.4 61.1 62.6

57.7 59.5 61.2 62.7

57.9 59.7 61.3 62.9

58.1 59.8 61.5 63.0

58.2 60.0 61.6 63.1

58.4 60.1 61.7 63.2

58.5 60.2 61.9 63.4

58.7 60.4 62.0 63.5

58.8 60.5 62.1 63.6

16 17 18 19 20

63.7 65.1 66.4 67.7 68.9

63.8 65.2 66.5 67.8 69.0

64.0 65.3 66.6 67.9 69.0

64.1 65.5 66.8 68.0 69.1

64.2 65.7 66.9 68.1 69.2

64.3 65.7 67.0 68.2 69.3

64.4 65.8 67.1 68.3 69.4

64.6 65.9 67.2 68.4 69.5

64.7 66.0 67.3 68.5 69.6

64.8 66.1 67.4 68.6 69.7

64.9 66.2 67.5 68.7 69.8

65.0 66.3 67.6 68.8 69.9

0 1 2 3

-

The inductive reactance spacing factors in the above table are given in microhms per foot. Spacings are total distance between conductors. To convert these values of inductive reactance to any other frequency, multiply by the ratio of the two frequencies, for example: XL2

Where: X L2

=

f

X oo X 60

is the value desired at the frequency f.

6

-15.9 ' -12.4 9.3 10.6 21.1 21.8 28.8 29.3

8

-

9.3 11.7 22.5 29.9

9

-

6.6 12.9 23.2 30.4

11

10

-

4.2 13.9 23.9 30.9

-

2.0 15.0 24.6 31.4

The 60 cps inductive reactance spacing factors in this table are calculated by the following formula: XL2 = 52.91 Log10 GMD (Microhms per foot). The GMD is the equivalent spacing of the circuit and for a 3 phase configuration is given by the formula,

GMD = iY A X B X C Where: A, B, and C are the total spacings between conductors.

137


BARE, ALL ALUMINUM STRANDED CONDUCTOR, HARD DRAWN (Physical Dimensions and Breaking Strength) AREA

Cable

E'buivalent H . . Copper AWGor CM(2)

Breaking Strength (Pounds) (3)

Code Word (for harddrawn only)

Size AWGor CM(I)

Square Inches

Square mm

Stranding Class

Total Number of Strands

Wire Diameter (Inches)

Diameter

Peachbell Rose Lily Iris Pansy

*6 *4 3 *2 1

0.02061 0.03278 0.04133 0.05212 0.06573

13.30 21.15 26.66 33.63 42.41

A-B A-B A-B AA-A-B AA-A

7 7 7 7 7

0.0612 0.0772 0.0867 0.0974 0.1093

0.1836 0.2316 0.2601 0.2922 0.3279

No.8 No.6 No.5 No.4 No.3

529 826 1,023 1,267 1,538

1/0 *1/0 2/0 *2/0

0.08291 0.08291 0.1045 0.1045

53.49 53.49 67.42 67.42

AA-A B AA-A B

7 19 7 19

0.1228 0.0745 0.1379 0.0837

0.3684 0.3725 0.4137 0.4185

No.2 No.2 No.1 No.1

1,864 2,088 2,351 2,586

jj~~d~lion

3/0 *3/0 4/0 *4/0 250,000 *250,000

0.1318 0.1318 0.1662 0.1662 0.1963 0.1963

85.03 85.03 107.2 107.2 126.6 126.6

AA-A B AA-A B A B

7 19 7 19 19 37

0.1548 0.0940 0.1739 0.1055 0.1147 0.0822

0.4644 0.4700 0.5217 0.5275 0.5735 0.5754

No.lIO No. 1/0 No. 2/0 No. 2/0 157,200 157,200

2,847 3,203 3,590 3,889 4,506 4,858

Daisy Laurel Foxglove Peony Agave

266,800 266,800 *266,800 300,000 *300,000

0.2095 0.2095 0.2095 0.2356 0.2356

135.2 135.2 135.2 152.0 152.0

-A

B A B

7 19 37 19 37

0.1953 0.1185 0.0849 0.1257 0.0900

0.5859 0.5925 0.5943 0.6285 0.6300

No. 3/0 No. 3/0 No. 3/0 188,700 188,700

4,525 4,808 5,185 5,301 5,831

Tulip Hollyhock Daffodil Gardenia Canna

336,400 *336,400 350,000 *350,000 397,500

0.2642 0.2642 0.2749 0.2749 0.3122

170.5 170.5 177.4 177.4 201.4

A B A B AA-A

19 37 19 37 19

0.1331 0.0954 0.1357 0.0973 0.1447

0.6655 0.6678 0.6785 0.6811 0.7235

No. 4/0 No. 4/0 220,000 220,000 250,000

5,945 6,420 6,185 6,680 6,884

...... ...... ......

400,000 *400,000 450,000 *450,000 477,000 477,000

0.3142 0.3142 0.3534 0.3534 0.3746 0.3746

202.7 202.7 228.0 228.0 241.7 241.7

AA-A B All. A-B AA A-B

19 37 19 37 19 37

0.1451 0.1040 0.1539 0.1103 0.1585 0.1135

0.7255 0.7280 0.7695 0.7721 0.7925 0.7945

252,000 252,000 283,000 283,000 300,000 300,000

6,928 7,352 7,633 8,111 8,091 8,591

500,000 *500,000 556,500 556,500 *600,000

0.3927 0.3927 0.4371 0.4371 0.4712

253.4 253.4 282.0 282.0 304.0

AA A-B AA-A B

19 37 19 37 61

0.1622 0.1162 0.1711 0.1226 0.0992

0.8110 0.8134 0.8555 0.8582 0.8928

314,000 314,000 350,000 350,000 377,000

8,482 9,012 9,436 9,828 11,450

Fi~(

636,000 636,000 *700,000 715,500 715,500

0.4995 0.4995 0.5498 0.5620 0.5620

322.3 322.3 354.7 362.6 362.6

AA-A B A-B All. A-B

37 61 61 37 61

0.1311 0.1021 0.1071 0.1391 0.1083

0.9177 0.9189 0.9639 0.9737 0.9747

400,000 400,000 440,000 450,000 450,000

11,240 11,690 12,860 12,640 13,150

Petunia Cattail Arbutus Lilac

*750,000 750,000 *795,000 795,000 *800,00U

0.5890 0.5890 0.6244 0.6244 0.6283

380.0 380.0 402.8 402.8 405.4

All. A-B All. A-B A-B

37 61 37 61 61

0.1424 0.1109 0.1466 0.1142 0.1145

0.9968 0.9981 1.0262 1.0278 1.0305

472,000 472,000 500,000 500,000 503,000

12,990 13,520 13,770 14,340 14,420

Anemone Crocus Magnolia Goldenrod

874,500 874,500 954,000 954,000

0.6868 0.6868 0.7493 0.7493

443.1 443.1 483.4 483.4

All. A-B All. A-B

37 61 37 61

0.1538 0.1198 0.1606 0.1251

1.0766 1.0782 1.1242 1.1259

550,000 550,000 600,000 600,000

14,830 15,780 16,180 16,870

Camellia Bluebell Larkspur Marigold Hawthorn

*1,000,000 1,033,500 1,033,500 1,113,000 1,192,500

0.7854 0.8117 0.8117 0.8741 0.9366

506.7 523.7 523.7 563.9 604.3

A-B All. AA-A AA-A AA-A

61 37 61 61 61

0.1280 0.1672 0.1302 0.1351 0.1398

1.1520 1.1704 1.1718 1.2159 1.2582

629,000 650,000 650,000 700,000 750,000

17,670 17,530 18.270 19;670 21,070

Narcissus

1.272,000 1,351,500 1.431,000 1.510,500 1.590.000

0.9990 1.061 1.124 1.186 1.249

644.5 684.5 725.2 765.2 805.8

AA-A AA-A AA-A AA-A AA-A

61 61 61 61 61

0.1444 0.1489 0.1532 0.1574 0.1615

1.2996 1.3401 1.3788 1.4166 1.4535

800,000 850,000 900,000 950,000 "1,000.000

22,030 23,400 24,280 25,620 26,980

Poppy Geranium

Aster Buttercup Phlox Primrose

Oxlip

Sunflower

C·~s~~s Syringa Zinnia

Hyacinth Dahlia Mistletoe Lotus Orchid Vio et Nasturtium

......

Columbine Carnation Gladiolus Coreopsis

(1) The sizes marked with an asterisk are usually used for insulated conductors. For conductors to be insulated, a left-hand lay should be specified for the outer layer of wires. Bare conductors for overhead usc are normally furnished with a right-hand lay on the outer layer of wires unless otherwise specified. (2) For hard drawn copper conductor 97 per cent conductivity, lACS, havino; approximately the same doc resistance as aluminum conductor of 61 per cent conductivity, lACS, at 20 C.

138

(Inches)

(3) The breaking stren~th is 90 per cent of the total of all the individual strand average tensile strengths as given in ASTM B230 for hard drawn wire.

NOTE: These data are approximate and subject to normal manufacturing tolerances. Data subject to change without notice.


BARE, ALL ALUMINUM STRANDED CONDUCTOR, HARD DRAWN (Electrical Characteristics and Weight) 60 cps Inductive Current

Code Word (for harddrawn only)

Size AWG or MCM

Stranding

RESISTANCE(2) (Ohms per 1000 feet)

Reactance

Carrying Capacity (1 ) (Amperes)

Geometric Mean Radius , GMR (Feet)

for I-foot

WEIGHT

at 70 C

spacing

at 20 C

(Ohms per 1000 ft.)

(D-C)

(D-C)

60 cps

Pounds per 1000'

Pounds per Mile

6 4 3 2 1

7 7 7 7 7

80 105 120 140 165

0.005551 0.007003 0.007864 0.008835 0.009914

0.1194 0.1140 0.1114 0.1087 0.1060

0.6613 0.4157 0.3297 0.2615 0.2073

0.7945 0.4995 0.3962 0.3142 0.2491

0.7945 0.4995 0.3962 0.3142 0.2492

24.6 39.2 49.4 62.3 78.6

130 207 261 329 415

1/0 1/0 2/0 2/0

7 19 7 19

190 190 220 220

0.01114 0.01176 0.01251 0.01321

0.1033 0.1021 0.1007 0.09943

0.1643 0.1643 0.1304 0.1304

0.1974 0.1974 0.1566 0.1566

0.1975 0.1975 0.1567 0.1567

99.0 99.0 124.9 124.9

523 523 660 660

D~~d~lion

3/0 3/0 4/0 4/0 250 250

7 19 7 19 19 37

255 255 300 300 335 335

0.01404 0.01484 0.01577 0.01665 0.01810 0.01841

0.09803 0.09676 0.09536 0.09411 0.09220 0.09180

0.1034 0.1034 0.08200 0.08200 0.06940 0.06940

0.1242 0.1242 0.09852 0.09852 0.08339 0.08339

0.1243 0.1243 0.09863 0.09863 0.08352 0.08352

157.5 157.5 198.6 198.6 234.7 234.7

832 832 1049 1049 1239 1239

Daisy Laurel Foxglove Peony Agave

266.8 266.8 266.8 300 300

7 19 37 19 37

345 345 350 375 375

0.01772 0.01870 0.01901 0.01984 0.02016

0.09268 0.09145 0.09107 0.09009 0.08972

0.06503 0.06503 0.06503 0.05784 0.05784

0.07814 0.07814 0.07814 0.06949 0.06949

0.07828 0.07828 0.07828 0.06965 0.06965

250.5 250.5 250.5 281.6 281.6

1322 1322 1322 1487 1487

Tulip Hollyhock Daffodil Gardenia

336.4 336.4 350 350 397.5

19 37 19 37 19

405 405 415 415 450

0.02101 0.02136 0.02142 0.02179 0.02284

0.08877 0.08839 0.08832 0.08793 0.08685

0.05158 0.05158 0.04957 0.04957 0.04365

0.06197 0.06197 . 0.05956 0.05956 0.05245

0.06215 0.06215 0.05975 0.05975 0.05266

315.8 315.8 328.6 328.6 373.2

1667 1667 1735 1735 1970

Syringa

400 400 450 450 477 477

19 37 19 37 19 37

450 450 490 490 505 505

0.02290 0.02329 0.02429 0.02470 0.02502 0.02542

0.08679 0.08640 0.08544 0.08505 0.08475 0.08439

0.04338 0.04338 0.03856 0.03856 0.03638 0.03638

0.05212 0.05212 0.04633 0.04633 0.04371 0.04371

0.05234 0.05234 0.04656 0.04656 0.04396 0.04396

375.5 375.5 422.4 422.4 447.8 447.8

1983 1983 2230 2230 2364 2364

Zinnia Hyacinth Dahlia Mistletoe Lotus

500 500 556.5 556.5 600

19 37 19 37 61

520 520 560 560 590

0.02560 0.02602 0.02700 0.02746 0.02872

0.08423 0.08385 0.08300 0.08262 0.08159

0.03470 0.03470 0.03118 0.03118 0.02892

0.04169 0.04169 0.03746 0.03746 0.03475

0.04195 0.04195 0.03775 0.03775 0.03506

469.4 469.4 522.4 522.4 563.2

24-78 2478 2758 2758 2974

Orchid

636 636 700 715.5 715.5

37 61 61 37 61

610 610 650 660 660

0.02936 0.02956 0.03101 0.03115 0.03135

0.08108 0.08092 0.07982 0.07972 0.07957

0.02728 0.02728 0.02479 0.02425 0.02425

0.03278 0.03278 0.02978 0.02914 0.02914

0.03311 0.03311 0.03015 0.02951 0.02951

597.0 597.0 657.1 671.7 671.7

3152 3152 3469 3547 3547

750 750 795 795 800

37 61 37 61 61

680 680 705 705 705

0.03189 0.03?!1 0.03283 0.03306 0.03315

0.07918 0.07902 0.07851 0.07835 0.07829

. 0.02313 0.02313 0.02183 0.02183 0.02169

0.02782 0.02782 0.02622 0.02622 0.02606

0.02821 0.02821 0.02664 0.02664 0.02648

704.0 704.0 746.3 746.3 751.0

3717 3717 3940 3940 3965

Magnolia Goldenrod

874.5 874.5 954 954

37 61 37 61

750 750 790 790

0.03444 0.03468 0.03597 0.03622

0.07741 0.07725 0.07641 0.07626

0.01984 0.01984 0.01819 0.01819

0.02384 0.02384 0.02185 0.02185

0.02429 0.02429 0.02235 0.02235

820.9 820.9 895.6 895.6

4334 4334 4729 4729

Camellia Bluebell Larkspur Marigold Hawthorn

1000 1033.5 1033.5 1113 1192.5

61 37 61 61 61

815 830 830 870 910

0.03706 0.03744 0.03769 0.03911 0.04047

0.07573 0.07549 0.07534 0.07449 0.07370

0.01735 0.01679 0.01679 0.01559 0.01455

0.02085 0.02017 0.02017 0.01873 0.01748

0.02136 0.02071 0.02071 0.01930 0.01809

938.7 970.2 970.2 1045 1119

4956 5123 5123 5518 5908

Narcissus Columbine

1272 1351.5 1431 1510.5 1590

61 61 61 61 61

945 985 1020 1050 1085

0.04180 0.04311 0.04435 0.04557 0.04675

0.07296 0.07225 0.07160 0.07098 0.07039

0.01364 0.01284 0.01213 0.01149 0.01091

0.01639 0.01543 0.01457 0.01380 0.01311

0.01704 0.01611 0.01529 0.01457 0.01391

1194 1268 1343 1418 1493

6304 6695 7091 7487 7883

Peachbell Rose Lily Iris Pansy Poppy Geranium

Aster Buttercup Phlox Primrose

Oxlip Sunflower

Canna

...... ...... ...... c·o·s;";~s

Fi~g" Violet Nasturtium Petunia

Cattail Arbutus Lilac

......

Anemone Crocus

Carnation

Gladiolus Coreopsis

(1) Current Carrying Capacity based on methods of calculation by Sehurig & Frick, "Heating and Current Carrying Capacity of Bare Conductors for Outdoor Service," G. E. Review, Vol. 33, No.3, March 1930, page 141, for a wind velocity of 2 feet per sec., ambient air temperature of 40 C, conductor maximum temperature of 70 C, and a tarnished surface with an emissivity of e 0.5.

=

(2) D-C resistance based on 60.97 per cent conductivity aluminum lACS with a resistivity of 17.011 ohms (mil, foot) at 20 C with standard increments added for stranding per ASTM Specification B231. A-C resistance values include skin effect. NOTE: These data are approximate and subject to normal manufacturing tolerances. Data subject to change without notice.

139


NEW DESIGNATIONS FOn ALUMINUM ALLOYS Wrought aluminum and wrought aluminum alloys are designated by a four digit index system. Temper designations are not changed and follow the alloy designations. The new system of four-digit numbers, effective October 1, 1954, is expected to meet all present and future needs for wrought alloy designations. To aid in the transition to the new system, many of the old numbers are retained as the last two digits of the new numbers. The first digit of the designation serves to indicate alloy groups as shown in Table I. The last two digits identify the aluminum alloy or indicate the aluminum purity. The second digit indicates modifications of the original alloy or impurity limits. Although most aluminum alloys contain several alloying elements, the major groups are determined by the major alloying element. Except that one group, 6x:xx for alloys with magnesium and silicon as major alloying elements, designates two elements as indicated in Table 1. In the lx:xx group for aluminum of 99.00 per cent minimum and greater, the last two digits indicate the minimum aluminum percentage to the nearest 0.01 per cent above the 99.000 base amount. The second digit in the designation of the lxxx group indicates modifications in impurity limits. If the second digit is zero, there is no special control on individual impurities; while integers 1 through 9 (assigned consecutively as needed) indicate special control of one or more individual impurities. Thus 1030 indicates 99.30 per cent minimum aluminum without special control on individual impurities; and 1130, 1230, 1330, indicate the same purity with special control of one or more impurities as designated by the second integer 1, 2, and 3. '

TABLE I-NEW DESIGNATIONS FOR ALUMINUM ALLOY GROUPS AA Number

Aluminum-99.00 per cent minimum and greater .... " .1= MAJOR ALLOYING ELEMENT

Copper

Aluminum alloys grouped by . 11' 1 major a oymg e ements. .

Unused series

. . . .. 2= ~anganese . . . . . . . . . .. 3= Silicon. . . . . . . . . . . . .. 4= ~agnesium 5= ~agnesium and Silicon. 6= Zinc 7= Other element 8= " 9=

(1) EC-The designation for electrical conductor metal is not being changed since it is so firmly established in the electrical industry. (2) No.1 Reflector Sheet.

140

TABLE II-ALUMINUM ALLOY DESIGNATION CONVERSIONS NEW AA Number

OLD Commercial Designation

EC(l) 1030 1050 1060 1070

EC AE1S AD1S BD1S AC1S

1075 1080 1085 1090 1095

JC1S BC1S AB1S FB1S AA1S

1099 1100 1130(2) 1145 1150

BA1S 2S R308 BE1S ED1S

1160 1175(3) 1180 1187 1197

CD1S, 99.6 99.75 CC1S,R998 EB1S, 99.87 CA1S

1230(4) 1235 2011 2014 2017

99.3 R995 l1S 14S, R301 Core 17S

2018 2024 2025 2117 X2214

18S 24S 25S A17S XB14S

2218 2225 X2316 2618 3003

B18S B25S XC16S F18S 3S

3004 X3005

4S XA5S

NEW

OLD

AA Number

Commercial Designation

4032 4043 4045

32S 43S, K145 45S

4343 C43S, 44S, K143 X4543 XE43S 5005 A50S, R305, K155 5050 50S 5052 52S 5056 5083 5086 5154 5254 X5356 5357 X5405 5652 6003(5)

56S LK183 K186 A54S B54S XC56S C57S, K157 XD50S F52S R306, K162

6053 6061 6062 6063 6066

53S 61S 62S 63S 66S

6151 X6251 6253 X6453 6553

A51S XB51S B53S XD5.3S E53S

6951 7070 7072 7075 X7178

J51S, K160 70S 72S 75S XA78S

7277 8099 8112 X8280

B77S R399 K112 XB80S

(3) Cladding on No.2 Reflector Sheet. (4) Cladding on Alclad 2024 (Alclad 24S). (5) Cladding on Alclad 2014 (R301 and Alclad 14S).

tables and specificatiol1s - sectiol1 VI

ALUMINUM ASSOCIATION DESIGNATIONS AND EQUIVALENT ASTM DESIGNATIONS

WROUGHT ALUMINUM ALLOYS ASTM

AA

ASTM

CAST ALUMINUM ALLOYS

AA

990A MIA MGllA

1100 3003 3004

CG42A GR20A GSllB

2024 5052 6053

CB60A CM41A

2011 2017

GSllA GSI0A

6061 6063

ASTM

AA

S12A * S12B S5B SC54A ** CS72A

13 13 43 85 113

* Outmoded Desig. S5 ** Outmoded Desig. SC2

AA

ASTM

CZ72A C4A SC64C SC51A SG70A SC84B***

112 195 Alcast 60 355 356 A380

*** Outmoded Desig.

SC7

ALUMINUM EXTRUDED SHAPES AND EXTRUDED ROD AND BAR Standard Tolerances (6) (7) CROSS·SECTIONAL DIMENSIONS COl.2

COL. 4

NOTE 131

COlS.4,5,6.7

COL. 3

CO~

2

COL. 2~..J,..:=::::::;==:"":::;::===:;;:==:::=JTOLERANCE (1) (2) (Inch)

SPECIFIED DIMENSIONS (Inches)

METAL DIMENSIONS

SPACE DIMENSIONS

Allowable deviation from specified dimension where 75 per cent Or more of the dimension is metal

Allowable deviation from specified dimension where more than 25 per cent of the dimension is space (3) (4)

All excePtin~ those covere by column 3 Column 1

Column 2

Under 0.125 0.125 to (not inc!.) 0.25 0.25 to (not incl.) 0.5 0.5 to (not inc!.) 0.75

±0.006 ±0.007 ±0.008 ±0.009

0.75 1 1.5 2

I

Wall thickness (5) completely enclosing space 0.11 sq. in. and over (Eccentricity )

At dimensioned points 1,4 inch to 4notinCl.) inch from ase of leg

Column 3

Column 4

At dimensioned points % inch to (not incl.) 11~ inch from ase of leg

At dimensioned points 114 inch to (not incl.) 21\ inches from ase of leg

At dimensioned points 21h inche. or more from base of leg

Column 5

Column 6

Column 7

±0.010 ±0.012 ±0.014 ±0.016

±0.012 ±0.014 ±0.016 ±0.018

±0.014 ±0.016 ±0.018 ±0.020

±0.016 ±0.020 ±0.022 ±0.026

I

to to to to

(notinc!.) (not inc!.) (not inc!.) (not inc!.)

1 1.5 2 4

±0.010 ±0.012 ±0.016 ±0.024

Plus or minus 10 per cent

±0.018 ±0.020 ±0.024 ±0.032

±0.020 ±0.022 ±0.028 ±0.036

±0.022 ±0.026 ±0.034 ±0.048

±0.030 ±0.034 ±0.050 ±0.064

4 6 8 10

to to to to

(not inc!.) (not inc!.) (not inc!.) (not inc!.)

6 8 10 12

±0.034 ±0.044 ±0.054 ±0.064

max. ±0.060 min. ±0.01O

±0.042 ±0.054 ±0.064 ±0.074

±0.050 ±0.062 ±0.074 ±0.088

±0.064 ±0.082 ±0.100 ±0.116

±0.088 ±0.112 ±0.136 ±0.160

12 14

to (notinc!.) 14 to (incl.) 15

±0.074 ±0.080

±0.084 ±0.090

±0.100 ±0.106

±0.134 ±0.142

±0.184 ±0.196

(1 ) The tolerance applicable to a dimension composed of two or more component dimensions is the sum of the tolerances of the component dimensions, if all of the component dimensions are indicated. (2) When a dimension tolerance is specified other than as an equal bilateral tolerance, the value of the standard tolerance is that which would apply to the mean of the maximum and minimum dimensions permissible under the tolerance. (3) At points less than ;i inch from base of leg, the tolerances in Co!. 2 are applicable.

(4) Where the space is completely enclosed (hollow shapes), the tolerances in Col. 4 are applicable. (5) In the case of Class 1 Hollow Shapes, allowable deviation is plus or minus 10 per cent of mean wall thickness, max. ±0.060, min. ±0.010. (6) These Standard Tolerances are applicable to the average shape. Tolerances wider than standard may be necessary for some shapes; tolerances closer than standard may be possible for others. (7) These Standard Tolerances conform to the standards of The Aluminum Association, Extrusion Division.

141


ILLUSTRATIONS - STANDARD TOLERANCES - CROSS·SECTIONAL DIMENSIONS I - Closed Space Dimensions

X ICOL 4)

X (COL 4) Y (COL 2) X (COL 4)

All dimensions designated "Y" are classed as "metal dimensions" and tolerances are determined from column 2. Dimensions designated "X" are classed as "space dimensions through an enclosed void" and the tolerances applicable are determined from column 4 unless 75 per cent or more of the dimension is metal, in which case Column 2 applies.

II - Open Space Dimensions

~ ~X--i

If TB ~ _--1 L A Y

Tolerances applicable to dimensions "X" ar.. determined as follows: 1. locate dimension "X" in column 1. 2. Determine which of columns 4, 5, 6 or 7 is applicable, dependent upon distance "A." 3. locate proper tolerance in column 4, 5, 6 or 7 in the same line as dimension "X." Dimensions "Y" are "metal dimensions"; tolerances are determined from column 2. Distances "B" are shown merely to indicate incorrect values for determining which of columns 4, 5, 6 or 7 apply.

r-x--J

~rn f--B---J

Y Tolerances applicable to dimensions "X" are determined as follows: 1. locate dimension "X" in column 1. 2. Determine which of columns 4, 5, 6 or 7 is applicable, dependent upon distance "A." 3. locate proper tolerance in column 4, 5, 6 or 7 in the same line

as dimension "X." Dimension

llyll

is a

II

Tolerances applicable to dimensions "X" are determined as follows: 1. locate distance "B" in column 1. 2. Determine which of columns 4, 5, 6 or 7 is applicable, dependent upon distance itA. II

3. locate proper tolerance in column 4, 5, 6 or 7 in same line as value chose'n in column 1.

metol dimension"; tolerance is determined from column 2.

Tolerances applicable to dimension "X" are determined by standard tolerances applicable to angles "A".

142

tables and specifications - sectwn v 1

ALUMINUM EXTRUDED SHAPES AND EXTRUDED ROD AND BAR (Concluded) Standard Tolerances (4) (5) LENGTH *

STRAIGHTNESS

Tolerance (Inches) Circumscribing circle diam-

eter (shapes); specified diameter (rod); specified width

or depth, whichever greater

(bar (Inches)

Under 3.000 ......... 3.000-7.999 .......... 8.000 and over ........

Allowable deviation from specified length Specified length (Feet) Up Through 12

Over 12 Through 30

Over 30 Through 50

Over 50 --~

+Ys

+% +916 +%

+%6 +%

+% +%6 +~~

+1 +1 +1 TOLERANCE (2,3) (INCH)

*Applicable to straight length only. Circumscribing circle diameter (1)

TWIST

Allowable deviation from straight

Minimum

thickness (inches)

(inch'S)

In each foot of length

In total length of piece

Under 1% Under 1%

0.094 or under 0.050 (3) Over 0.094 0.0125

Length, ft., X 0.050 Length, ft., X 0.0125

1% and over

............

Length, ft., X 0.0125

0.0125

(1) The circumscribing circle diameter is the diameter of the smallest circle

that will completely enclose the shape.

(2) Not appli~able to extruded shapes in the !,~ne.aled ("9':) temper. (3) When welght of shape On flat 'surface m1111mIZeS deVIatIOn.

ANGULARITY TOLERANCE (DEGREES) TOLERANCE (2) (DEGREES)

(inches)

In each foot of length

Under 1% Ph to (notincl.) 3

1 degree % degree

3 andover

% degree

from s)'eeified angle

Length, ft., X 1 degree Length, ft., X % degree not over 5 degrees Length, ft., X % degree not over 3 degrees

Under 0.188 0.188to (notincl.) 0.750 0.750 to solid

CURVED SURFACES: Allowable deviation from specified inch per inch of chord length,

minimum not applicable to more than

90

0.005

inch

. . .

±2 ±1% ±1

CORNER AND FILLET RADII TOLERANCE (INCH)

SPECIFIED RADIUS (INCHES)

that will completely enclose the shape. (2) Not applicable to extruded shapes in the annealed ("0") tem)'er.

0.005

deviation

In total length of piece

(1) The circumscribing circle diameter is the diameter of the smallest circle

contour,

Allowable

MINIMUM SPECIFIED LEG THICKNESS (INCHES)

Allowable deviation from straight

Circumscribing circle diameter (1)

Sharp corners Under 0.188 0.188 and over

degrees of any

Allowable deviation from specified radius

+164, ±164,

. . .

± 10 per cent

EXTRUSION" TOLERANCE TERMINOLOGY

arc.

KAISER ALUMINUM STANDARD TOLERANCES are those (and only those) published FLAT SURFACES:

in

Kaiser Aluminum Stand-

ard Tolerances Engineering Data. To avoid misunder-

Allowable

0.004

standing they should be referred to as "Kaiser Aluminum

inch per inch of width;

Standard Tolerances," and not as "commercial" or "published" tolerances. .

deviation

0.004

from

flat,

inch minimum.

I

A

L

A SPECIAL tolerance is any tolerance that is closer or wider than Kaiser Aluminum Standard, whatever shape applied to.

CUT ENDS: Allowable deviation from square-l degree.

A CLOSE tolerance is any Special tolerance that is closer

(4) These Standard Tolerances are applicable to the average shape. Toler-

than Kaiser Aluminum Standard.

closer than standard may be possible for others. (5) These Standard Tolerances conform to the standards of The Aluminum

than Kaiser Aluminum Standard.

ances wider than standard may be necessary for some shapes; tolerances Association) E.xtrusiol1 Division.

A WIDE tolerance is any Special tolerance that is wider

143


PHYSICAL REQUIREMENTS FOR BOLTS, CAPSCREWS, STUDS, AND NUTS

*

SAE STANDARD

Scope-These specifications cover the physical requirements for steel bolts, capscrews, studs, and nuts used in the automotive and other industries. Whenever the term ''bolt'' is used, it is understood to include capscrews, studs, and similar externally threaded fasteners. General Data-The following grades are included: Grade O-Bolts without physical requirements; Grade I-Commercial steel bolts; Grade 2-Low-carbon steel bolts; Gi-ade 3-Medium-carbon steel, cold-worked, hexagon-head bolts and studs; Grade 5-Medium-carbon steel, quenched-and-tempered bolts; Grade 6-Medium-carbon steel, quenched-and-tempered, high-strength bolts; Grade 7-Medium-carbon alloy steel, quenchedand-tempered, medium-strength bolts; Grade 8-Medium-carbon alloy steel, quenchedand-tempered, high-strength bolts. For Grade and Grade 1 bolts and all nuts, openhearth, electric-furnace, or Bessemer steel may be used. For all other grades, open-hearth or electric-furnace steel shall be used. Unless otherwise specified, there are no limitations on the composition of the steels used, thus giving the manufacturer freedom in the selection of steels which will provide the required physical properties. It is intended that nuts shall be designated by grades, the same as bolts. Each grade of nut shall be required to meet the strip-load requirements which are equal to the minimum tensile strength of the corresponding grade of bolt. These are shown in Table 4. It is recommended that nuts be supplied in Grades 2, 5, and 8. Grade 2 nuts will pull Grades 0, 1, and 2 bolts. Grade 5 nuts will pull all grades of bolts up to and including Grade 5. Grade 8 nuts will pull all grades of bolts up to and including Grade 8.

°

Grades and Requirements-The various grades and their requirements are shown in Table 1. The following additional requirements apply. Wedge Test-Bolts and capscrews shall be subjected to a wedge test, the details of which are given under Methods of Testing. The wedge test on special-formed or drilled-head bolts shall be conducted with the lO-degree wedge under the nut. This also applies to studs (wedge at fine-threaded end) .

* Report

of Iron and Steel Technical Committee approved January 1949 and last revised December 1953.

144

Physical Properties-Bolts shall meet the hardness requirements prescribed in Table 1. When tested in full size for tensile properties, bolts shall also meet the tensile-strength and proof-load requirements specified in Table 4. Tensile requirements will be waived for bolts with special or drilled heads which are weaker than the threads. When bolts are too large for a full-size tension test, (usually above % inch in diameter), machined specimens shall have the minimum tensHe strength, yield strength, elongation, and reduction of area specified in ,Table 2. When bolts or thread lengths are too short for a tension test, acceptance shall be determined by the hardness range specified in Table 1. TABLEI--TENS~E,PROOFLOAD,AND

HARDNESS REQUIREMENTS Grade, Description, and Size (Dia.)

Minimtnn Tensile Strength (psi)

-

Grade Q-No requirements ...... Grade I-Commercial Steel Bolts 55,000 Grade 21 -Low-Carbon Steel Bolts (6 in. in length and under) Up to Ih in................. 69,000 Ih to % in.................. 64,000 % to l:1h in................ 55,000 (over 6 In. in length) All diameters .............. 55,000 Grade 3'-Medium-Carbon Steel, Cold-Worked, Hexagon-Head Bolts and Studs Up to 1/2 in................. 110,000 Over 1/2 to % in............ 100,000 Grade 58 -Medium-Carbon Steel, Quenched-and-Tempered Bolts Up to % in................. 120,000 Over % to I in............. 115,000 Over I to I Ih in............ 105,000 Grade 6 160,800 197,050, 237,000

e~er,

1% 1% 1:1:2

14 5h.G %

7116 :1:2

% % 14

0/16 %

%6 :1:2

%6

% %

% 1 Ills

114 1% 1:1:2 Grade 8Medium-Carbon Alloy Steel, Quenched-andTempered, HighStrength Bolts

IMinimum tensile

Elastic proof load, bolts,lb

%6

Grade 7Medium-Carbon Alloy Steel, Quenched-andTempered, Medium-Strength Bolts

Coarse Thread

14 0/16 %

7116 :1:2

%6

% % % 1

llfs 1% 1% 1:Ih

Elastic proof load,

strength,1.

Minimum tensile strength, 1 bolts,lb

(1) Also proof load for nuts. (2) Proof loads shown apply only to hexagon-head bolts and studs.

Yield Strength (Autographic Stress-Strain Method) -By agreement between supplier and purchaser, the yield strength instead of proof load may be determined on the full-size bolt by using an autographic method approved by the purchaser. When this is done, the minimum yield strength at 0.2% offset method, in pounds, shall be equal to the values shown for Elastic Proof Load in Table 4.

the threaded portion of the bolt at a point one quarter of the nominal diameter from the axis of the bolt. This section shall be taken at a distance of one diameter from the end of the bolt. The preparation of test specimens and the method of performing the hardness tests shall be in conformity with the requirements appearing in the SAE Handbook.

Hardness-For final arbitration, the hardness of bolts shall be determined on a transverse section through

Stripping Test for Nuts-The sample nut shall be assembled on a hardened, threaded mandrel and the

147


load specified in Table 4 applied to the nut. Threads of the nut shall not strip at this load. If the threads of the mandrel are damaged during the test, the test shall be discarded. The mandrel shall be threaded to the American Standard Class 3 tolerance, except that the major diameter shall be the minimum major diameter with a plus tolerance of 0.002 in. If the unit tensile stress developed in the mandrel is required, the loads thus obtained shall be divided by the mean thread area as given in Table 3. Number of Tests-The requirements of these specifications are those met in continuous mass production for stock during which the manufacturer has made such sample inspections as to insure normally that the material is controlled within the specified limits. Three bolts may be selected for tension test from each lot of bolts, and three nuts may be selected for stripping test from each lot of nuts. A lot of bolts or nuts or both shall consist of 25,000 or fraction thereof for diameters ~ to % in. inclusive, 15,000 or fraction thereof for diameters over % to % in. inclusive, 5000 or fraction thereof for diameters over % to 1 in. inclusive, and 2500 or fraction thereof for diameters over 1 in.

Retest-Should any sample from the same lot fail to meet the requirements of a specified test, twice the number of samples shall be tested, in which case all of the additional samples shall meet the specifications. Identification-Bolt heads shall be marked to identify the manufacturer. In addition, the following bolt head markings are prescribed:

148

Grades 0, 1, and 2--No marking.

CD Grade 3-2 radial dashes 180 degrees apart.

Grade 5-3 radial dashes 120 degrees apart,

Grade 6-4 radial dashes 90 degrees apart.



TENTATIVE SPECIFICATIONS FOR ALUMINUM BARS FOR ELECTRICAL PURPOSES (BUS BARS)J. ASTM DESIGNATION: B 236 . 56 T Issued, 1948; Revised, 1952, 1955, 1956. 2 These Tentative Specifications have been approved by the sponsoring committee and accepted by the Society in accordance with established procedures, for use pending adoption as standard. Suggestions for revisions should be addressed to the Society at 1916 Race St., Philadelphia 3, Pa.

Scope 1. These specifications cover EC aluminum bus bar for electrical conductors as follows: Type A.-Cold finished rectangular bar in Hl3 and H17 tempers. . Type B.-Hot finished rectangular bar in H12, HU1, and Hll2 tempers.

Basis of Purchase 2. Orders for material under these specifications shall include the following information: (1) Pieces or pounds, (2) Temper (Section 4), ( 3) Dimensions-thickness, width, and length (specific or stock) (Section 10), ( 4) Edge contour (Section 15), (5) Finish (Section 16), ( 6) Whether marking for identification is required (Section 17), and ( 7) Place of inspection (Section 19).

sHe properties prescribed in Table I for the specified temper.

TABLE I.-TENSILE REQUIREMENTS. NOTE.-For purposes of determining conformance with these specifications, each value for tensile strength and yield strength shall be rounded off to the nearest 100 psi, in accordance with the rounding off method of the Recommended Practices for Designating Significant Places in Specified Limiting Values (ASTM Designation: E 29).

Temper

Thickness, in.

H17 ...... H13 ...... H12 ......

%to %, inc!.. .... %to %,inc!.. .... % to 1, incl....... % to %,inc!.. ....

H1l2 .....{

Over % to 1, inc!.. Over 1 to 1 Y.!, incl. All thicknesses. . ..

H11l .....

Tensile Strength, min, psi

Yield Strength, min, psi·

17000 14 000 12000 12000 11000 10 000 9 000

15000 12000 8 000 7000 5 000 4 000 4000

• Yield strength is defined as the stress which produces a permanent set of 0.2 per cent of the initial gage length.

Manufacture 3. The materials used shall be such as to produce bars that will comply with the requirements as to tensile properties, bend tests, and electrical conductivity prescribed in these specifications:

Tensile Properties 4. The bars shall be supplied in the temper specified and shall conform to the requirements as to ten1 Under the standardization procedure of the Society, these speciflcations are under the jurisdiction of the ASTM Committee B-7 on Light Metals and Alloys, Cast and Wrought. By publication of these specifications, the American Society for Testing Materials does not undertake to insure anyone utilizing the specifications against liability for infringement of Letters Patent nor assume any such liability, and such publication should not he construed as a recommendation of any patented or proprietary application that may be involved. 2 Latest revision accepted by the Society at the Annual Meeting, June,

1956.

Bend Properties 5. (a) Flatwise Bend Test.-Bars in the H12, H13, HIll, and H112 tempers shall be capable of being bent flatwise at room temperature through an angle of 90 deg around a pin having a radius equal to the thickness of the specimen, without cracking and with no apparent evidence of slivers or other imperfections. ( b) Edgewise Bend Test (See Note).-Bars in the H12, Hlll, and HI3 tempers, whose width-to-thickness values are not in excess of 12, 12, and 8 respectively, shall be capable of being bent cold edgewise 90 deg around a mandrel having the ramus shown in Table II, without cracking or excessive localized thinNOTE.-Edgewise bend tests are not required for bars over 4 in. in width.

149


Aluminum Bus Bars for Electrical Purposes (B 236 . 56 T) nings as defined below. Edgewise bends shall be considered satisfactory if the thickness within the vicinity of any localized thinning is not less than 90 per cent of the maximum thickness within the central 60 deg -of the bend when measured only along the outer edge of the bend.

TABLE n.-EDGEWISE BENDING RADIUS. Width of Bus Bar, in.

*

V2 and under. . . . . . . . . . . . . . . . . . . . . . . . . Over to 1, incl.. . . . . . . . . . . . . . . . . . . . . Over 1 to 1V2, incl.. . . . . . . . . . . . . . . . . . . . Over 1* to 2, incl.. . . . . . . . . . . . . . . . . . . . Over 2 to 2V2, incl. . . . . . . . . . . . . . . . . . . . . Over 2* to 3, incl.. . . . . . . . . . . . . . . . . . . . Over 3 to 3V2, incl. . . . . . . . . . . . . . . . . . . . . Over 3V2 to 4, incl.. . . . . . . . . . . . . . . . . . . .

Mandrel Radius, in.

V2 1 1V2

2

2V2 3

3V2 4

Electrical Properties 6. The resistivity of specimens selected as prescribed in Section 7 shall not exceed 0.07640 ohms (meter, gram) at 20 C (68 F) corresponding to a conductivity not less than 61 per cent of the International Annealed Copper Standard.

Test Specimens 7. (a) Tension.- Tension test specimens shall be the full section of the bar, or specimens machined from the bar with the axis parallel to the length of the bar and having the form and dimensions specified in the Methods of Tension Testing of Metallic Materials (ASTM Designation: E 8), for sheet type specimens or for round specimens. (b) Bend.-Bend test specimens shall be a full section of the material. (c) Resistivity or Conductivity.-Specimens for determining resistivity or conductivity should preferably be a full section of the material, but may be of any suitable size or shape appropriate to the instrument to be used in making the determination.

Number of Tests 8. (a) Specimens shall be selected from each size and temper of bars in the shipment according to the following schedule: Minil111U11 Number of Specimens to be Number of Pieces in Lot Selected It050...................... 1 51 to 200. .. . . . . . . . .. . . . . . . . . 2 201 to 1500. . . . . . . . . . . . . . . . . . 3 Over 1500 0.2 per cent of number of pieces in lot 150

( b) When more than one specimen is required to be taken from the lot, no two specimens for the same type of test shall be taken from the same bar.

Methods of Testing 9. (a) Tension.- Tension tests shall be made in accordance with the Methods of Tension Testing of Metallic Materials (ASTM Designation: E 8). NOTE.-The values obtained for the tensile properties covered by these specifications are not seriously affected by variations in speed of testing. A considerable range of testing speed is permissible, however, the rate of stressing to the yield sh'ength should not exceed 100,000 psi per min, and above the yield sh'ength the movement per minute of the head under load should not exceed 0.5 in. per in. of gage length (or distance between grips for specimens not having reduced sections). Care must be exercised, especially when making yield strength determinations, that the speed of testing does not exceed the ability of the strain and load-indicating equipment to function satisfactorily. (b) Bend.-Bend test specimens may be bent by either pressure or blows provided that, in the case of dispute, bends made under pressure shall be the basis of acceptance or rejection. (c) Electrical Resistivity. - Electrical resistivity shall be determined in accordance with the Method of Test for Resistivity of Electrical Conductor Materials (ASTM Designation: B 193).

TABLE III.-PERMISSIBLE VARIATIONS IN THICKNESS FOR TYPE A BARS. Specified Thickness, in.

Permissible Variations in Thickness, plus and minus, in.,. for Widths Given in Inches Over Over Over Over 2.00 to 4.00 to Yz to 1% 8.00, Yz and 1%, to 2.00, 4.00, inc!. inc!. Under incl. inc!.

0.125 to 0.188 0.0025 0.189 to 0.500 0.003 0.501 to 0.750 ....

0.0035 0.004 0.003 0.0035 0.004 0.0045 0.004 0.0045 0.005

0.0025 0.003 0.004

a If all plus or all minus variations are desired, double the values given.

TABLE IV.-PERMISSIBLE VARIATIONS IN WIDTH FOR TYPE A BARS. Permissible Variations in Width, plus and minus, in. a

Specified Width, in. 0.500 to 1.25 1.26 to 2.00 2.01 to 4.00 4.01 to 8.00

. . . .

0.005 0.008 0.012 0.30 per cent b

a When variations are specified as ali plus or all minus, doub the values given. b Expressed to the nearest 0.001 in.


Aluminum Bus Bars for Electrical Purposes (B 236 . 56 T) Permissible Variations in Dimensions 10. (a) Thickness and Width. _ Thickness and width variations from the specified dimensions for the type of bar ordered shall not exceed the amount prescribed in Tables III, IV, V, and VI.

terial is ordered in stock lengths, it may include short lengths as prescribed in Table VIII.

TABLE VII.-PERMISSIBLE VARIATIONS IN LENGTH FOR SPECIFIC AND MULTIPLE LENGTHS.

TABLE V.-PERMISSIBLE VARIATIONS IN THICKNESS FOR TYPE B BAR.

I

Thickness, in.

0.125 0.501 0.751 1.001

to to to to

0.500 0.750 1.000 2.000

. . . .

Specified Width, in.

Permissible Variations in Thickness, plus and minus, in.

18 and Under

3.499 and under. 3.500 and over

FINISHED EDGE

Permissible Variation in Inches over the Specified Length Given in Feet

0.006 0.008 0.012 0.020

. .

TABLE VID.-SCHEDULE OF LENGTHS (STOCK WITH SHORT LENGTHS).

SAWED EDGE

0.250 0.321 0.439 0.626 0.876 1.126 1.376 1.626 1.876 2.251 2.751

to to to to to to to to to to to

0.320. . . . . . . . . . . . . . . . . . . 0.438. . . . . . . . . . . . . . . . . . . 0.625. . . . . . . . . . . . . . . . . . . 0.875. . . . . . . . . . . . . . . . . . . 1.125. . . . . . . . . . . . . . . . . . . 1.375. . . . . . . . . . . . . . . . . . . 1.625. . . . . . . . . . . . . . . . . . . 1.875. . . . . . . . . . . . . . . . . . . 2.250. . . . . . . . . . . . . . . . . . . 2.750......... 3.000...................

0.013 0.019 0.025 0.030 0.035 0.040 0.045 0.052 0.060 0.075 0.090

TABLE VI.-PERMISSIBLE VARIATIONS IN WIDTH FOR TYPE B BAR. Width, in.

Permissible Variations in Width, plus and minus, in.

FINISHED EDGE

0.500 1.501 4.001 6.001

to to to to

1.500 " 4.000. . . . . . . . . . . . . . . . . . . 6.000. . . . . . . . . . . . . . . . . . . 10.000. . . . . . . . . . . . . . . . . .

0.016 0.032 0.047 0.063

Area, sq in. a

Stock Length, ft

0.250 and under Over 0.250 to 1, incl. Over 1 to 2.25, incl. Over 2.25 to 4, incl. Over 4 to 9, incl.

6 to 6 to 6 to 6 to 6 to

0.094 0.125

( b) Specified Lengths.-When exact lengths are ordered, the lengths shall not be less than the ordered length and not exceeded by more than prescribed in Table VII. ( c) Stock Lengths. - Material ordered in stock lengths shall be not less than the designated length and shall not exceed it by more than 1 in. When ma-

20, indo 20, indo 20, incl. 20, incl. 10, incl.

Shortest Permissible Length, b per cent of Nominal Length

75 70 70 60 60

Maxim.um Permissible Weight of Short Lengths, per cent of lot Weight

20 30 30 30

gO

• Width times thickness, disregarding any rounded corners or edges. Expressed to the nearest Y. ft.

b

Straightness 11. Unless otherwise speci£ed, the material shall be furnished in straight lengths. The deviation from straightness of any longitudinal surface or edge shall not exceed the limitations prescribed in Table IX. TABLE IX.-PERMISSIBLE VARIATIONS IN STRAIGHTNESS APPLICABLE TO ANY LONGITUDINAL SURFACE OR EDGE:

Type

Temper

SAWED EDGE

2.000 to 6.000. . . . . . . . . . . . . . . . . . . 6.001 to 14.000 ... , .... ,. . . . .. . ..

Over 18

H17 ..... A ........ { H13 ..... B........ All ......

Maximum Curvature (Depth of Arc), in. Flatwise

Edgewise

1;4 1;4 1;4

% % 1;4

Portion of Total Length in Which Depth of Arc is Measured, in.

96 60 60

NOTE.-To determine compliance w'ith this section, bar shall, in case of disagreement, be checked by the following method: Place the bar on a level table so that the arc or departure from straightness is horizontal. Measure the maximum depth of arc to the nearest 1~2 in. using a steel scale and a straight edge. 151


Aluminum Bus Bars for Electrical Purposes (B 236 -56 T) (c) Rounded Edge.-When specified, bar may be

Flatness

12. Flat surfaces of both type A and B material shall not deviate from flat by more than 0.004 in. per inch of width, with a deviation of 0.004 in. permitted for all widths under 1 in.

finished with edges rounded as shown in Fig. 2, the radius of curvature being approximately one and one quarter times the thickness of the bar for bar 1Js in. and over in thickness. The tolerance on the radius shall be one-fourth the thickness of the bar.

I·

Retests

i

13. If any test specimen fails to meet the applicable requirements of these specifications, two additional specimens shall be selected from other bars in the lot and both specimens shall meet the applicable requirements or the lot shall be subject to rejection.

Significance of Numerical Limits 14. For purposes of determining compliance with the specified limits for requirements of the properties listed in the following table, an observed value or a calculated value shall be rounded off as indicated in accordance with the rounding-off methods of the Recommended Practices for Designating Significant Places in Specified Limiting Values (ASTM Designation: E 29). Property

NOTE.-The arc shall be substantially symmetrical with the axis of the product. The corners will usually be sharp but shall not have rough or projecting edges. FIG. 2.-Rounded Edge.

(d) Full-Rounded Edge.-When specified, bar may be finished with substantially uniform round edges, the radius of curvature being approximately one-half the thickness of the product, as shown in Fig. 3, but in no case to exceed one-half the thickness of the product by more than 25 per cent.

Rounded-Off Unit for Observed or Calculated Value

Electrical resistivity ..... nearest unit in the last right hand place of figures Tensile strength . . . . . . . .nearest 500 psi Yield strength nearest 500 psi

Edge Contours 15. (a) Square Corners.- Unless otherwise specified, bar shall be finished with commercially square corners with a maximum permissible radius of Y:32 in. for bar lh in. to 1 in., inclusive, in thickness, and VJ.6 in. for bar over 1 in. in thickness. (b) Rounded Corners.-When specified, bar may be finished with corners rounded as shown in Fig. 1 to a quarter circle with a radius of Ys2 in. for bar VB to %6 in. inclusive, in thickness; VJ.6 in. for bar over %6 in. to 1 in. inclusive, in thickness; and lh in. for bar over 1 in. in thickness.

NOTE.-The arc shall not necessarily be tangent but the product shall be commercially free from sharp, rough or projecting edges. FIG. I.-Rounded Corners. 152

R

R

NOTE.-The arc shall not necessarily be tangent but shall be substantially symmetrical with the a..xis of the product, and the product shall be commercially free from sharp, rough, or projecting edges. FIG. 3.-Full Rounded Edge.

(e) Sawed Edge.-A rough surfaced edge showing saw marks and very slight or no deformation of the corners. The sawing operation leaves a slight burr on the corners, which is generally not completely removed and which may necessitate care in handling.

Finish 16. (a) Class I.-Material shall be free from blisters, slivers, and pick up, as well as from all other imperfections not consistent with the best commercial practice and shall be commercially bright and clean. It shall be suitable for use as electrical bus bar. . (b) Class n.-Material shall be uniform in quality and condition, free from laps, folds, slivers, seams, and cracks. Surface appearance as such is not a primary factor; and stains, abrasions, saw burrs, and minor handling marks within the limits of commercial practices shall be acceptable.


Aluminum Bus Bars for Electrical Purposes (B 236 . 56 T) Marking for Identification 11. (a) When identification marking is specified on the purchase order, all bars shall be marked with the manufacturer's name or trade mark and the applicable alloy and temper designations, the latter to be in accordance with the ASTM codification systems (ASTM Designation: B 275 and B 296) or the commercial systems. Identification characters shall have a minimum height of % in. The marking material shall be such as to resist obliteration during normal handling and shall be removable by normal cleaning methods; however, ghost images of the characters may remain. Markings shall appear at each end of each piece. ( b) The, foregoing requirements are minimum, marking systems which involve added information, larger characters, and greater frequencies are accept·able under these specifications.

Packaging 18. The material shall be properly and adequately bundled, crated, or otherwise packaged to protect it against injury during shipment. The type of packaging shall be left to the discretion of the manufacturer, unless otherwise agreed upon. Each package shall

contain only one size of material, unless otherwise agreed upon by the manufacturer and the purchaser.

Inspection 19. (a) Inspection may be made at the manufacturer's works or at the point at which the material is received, at the option of the purchaser. ( b) If the purchaser elects to have the inspection made at the manufacturer's works, the manufacturer shall afford the inspector representing the purchaser all reasonable facilities, ~thout charge, to satisfy him that the material is being furnished in accordance with these specifications. All tests and inspection shall be so conducted as not to interfere unnecessarily with the operation of the works.

Rejection 20. Material failing to conform to the requirements of these specifications or in which defects are discovered-during subsequent manufacturing operations may be rejected and, if rejected, the manufacturer's responsibility shall be limited to replacing the rejected material without charge to the purchaser. The full weight of the rejected original material shall be returned to the manufacturer.

Appendix The most common form of aluminum bus conductor is bar which, for purposes of this specification, is defined as follows: Bar.-Includes material of solid rectangular or square cross-section, or a solid section with two plane parallel sUlfaces having round or other simple regularshaped edges. Unless otherwise specified, bars are generally finished with commercially square corners in accordance with the definition in Section 15(a ). EC aluminum rectangular bar may be manufactured commercially by the following methods: (1) Hot-Rolled.-Hot-rolled to the final dimensions. (2) Extruded.-Extruded to the final dimensions. (3) Cold-Finished.-Hot-rolled or extruded to a size larger than specified and reduced to final dimensions by drawing or cold rolling. (4) As Fabricated Bar Sawed from Plate.-Hot- or cold-rolled to final thickness and sawed to final ~dth. . EC aluminum bar is normally selected on the basis of the desired strength requirements and bending characteristics required for fabrication and installa-

tion. Dimensional tolerances and surface finish may be of equal importance in some applications. Surface finish may be related to the method of fabrication. Commercial mill hot-finished bar, class II finish, is used where surface quality as such is not a primary requirement. By employing controlled fabricating practices, hot-worked bar may be produced to class I finish. This bar would have a variation in luster typical of a hot-worked finish, but fewer handling marks or other surface irregularities than class II finish. Cold working of the bar to finish it will, by the nature of this operation, result in a class I finish. It produces a more uniform finish as a result of the controlled fabricating practices employed. The harder tempers produced by cold finishing are less subject to abrasion marking. Bar produced with a class I finish requires boxing for proper protection during shipment. Some applications require that flat bus bar be bent either flatwise or edgewise. The specifications define the flatwise and edgewise bending requirements applicable to the various temper designations of bar. In

153


Aluminum Bus Bars for Electrical Purposes (B 236·56 T) general, the higher the tensile strength or the greater the thickness of the bar the greater the radius required to bend it flatwise without cracking. EC-H17 bar can be successfully bent 90 deg flatwise over a radius of one times the thickness, although slight surface cracking may sometimes develop. It is, therefore, suggested that a larger bending radius be employed for flatwise bending this temper. Edgewise bending is much more severe and is more difficult to do. Success in making satisfactory edgewise bends depends to a considerable extent upon the equipment and procedures used. The radius (in terms of width of bar) around which a bar can be bent edgewise depends upon the tensile properties and also upon the ratio of width to thickness, Wit, of the bar. When bars are bent edgewise the changes in dimensions appear to be a function of the geometry of the bend regardless of the tensile properties of the bar. With a bend radius of 1W, the thickness along the inner edge increases about 20 per cent, and along the outer edge it decreases about 16 per cent. For EC-H12 and EC-H13 a radius greater than 1W will normally be required for bars having a Wit exceeding 12 and 8, respectively. In special cases where these width thickness ratios are exceeded, a larger bend radius should be used. Table X reflects the in:8.uence of bar dimensions.

Samples for chemical analysis shall be taken in accordance with the Method of Sampling Wrought Non-Ferrous Metals and Alloys for Determination of Chemical Composition (ASTM Designation: E 55), except that the weight of the prepared sample may be a minimum of 75 g. A portion shall be taken to represent each 2,000 lb or fraction thereof of each temper and size of bars in the shipment, and a sample prepared from each portion. If agreed upon by the manufacturer and the purchaser, a composite sample representing all portions taken from a given temper and size may be used for the analysis in lieu of analyzing samples from each portion. If the manufacturer has made an analysis during the course of manufacture, he shall not be required to sample and analyze the finished product. The chemical analysis shall be made in accordance with the Method of Chemical Analysis of Aluminum and Aluminum-Base Alloys (ASTM Designation: E 34) 3 or by any other approved methods agreed upon by the manufacturer and the purchaser. The analysis may be made spectrochemically, provided that, in the case of dispute, the results secured by Methods E 34 shall be the basis for acceptance. 3

1956 Book of ASTM Methods for Chemical Analysis of Metals.

TABLE X.-·READILY AVAILABLE WIDTHS. Thickness, in.

Width, in.

1h

VB ....... .

% I 114 1112 1% --------

X X X X Y4 ....... . X X % .. . .... . . , . .. . liz ....... . . . .. . % .. . .... . . , . .. . % ....... . . . .. . 1 ........ . . . .. . %6 ...... .

,

, ,

X ® ® X X X X X X .. . .. . .. . .. . . .. .. . . .. .. . .. .

.. .

.. . .. .

.. .

.. .

.. .

2

214

21h

2%

3

31h

4

5

6

NOTE.-Symbols used in the table are explained as follows: X.-Hlll, Hl2 and Hl3 tempers required to meet edgewise bend test. 0.-HI3 temper not required to meet edgewise bend test. fRI.-Neither HIll, H12 nor Hl3 tempers required to meet edgewise bend test. * -Bending requirements for bar wider than 4 in. shall be as agreed upon by the manufacturer and the purchaser.

154

I 8

I 10

1-----

l8J l8J . , . .. . .. . .. . .. . .. . .. . .. . . .. ... ® ® ® l8J l8J l8J .. . .. . .. . ... . .. . .. .. X X ® ® ® ® l8J l8J * * * .. . X X X X X ® ® * * * ... .. . X X X X X .. . X * * * ... . . .. . .. . .. . .. . .. . ... X * * * * .. . .. . .. . .. . . .. .. . ... X * * * * .. . .. . .. . .. . . .. .. . ... X * * * *

RECOMMENDED PRACTICE FOR PREPARATION OF AND ELECTROPLATING ON ALITMINUM ALLOYS

1

ASTM DESIGNATION: B 253 . 53 Adopted, 1953. 2 !his Recommended Practice of the American Society for Testing Materials is Issued under the fixed designation B 253; the final number indicates the year of original adoption or, in the case of revision, the year of last revision.

Scope . 1. (a) Various metals are electrodeposited on alummum alloys to obtain a decorative finish or one which is more wear resistant or suitable for some other specific service. The electroplates applied for finish are usually chromium, nickel, copper, brass, silver, gold or modifications of these. Silver is applied to electrical equipment to decrease contact resistance or to improve smface conductivity; brass to facilitate vulcanization of rubber to aluminum; copper, nickel or tin for as. sembly by soft soldering; chromium to reduce fIiction and obtain increased resistance to wear; zinc to threaded parts where organic lubricants are not permissible; while tin is frequently employed to reduce friction on bearing surfaces. ( b) This recommended practice is presented as a guide for the plating of aluminum alloys. Electroplating of these alloys is commercially practical and economically sound. Aluminum alloys, however, do not respond satisfactorily to many of the usual preparatory procedures for plating; hence, different procedures are requir~d to obtain a satisfactory basis for plating. Of the dIfferent methods available, the zinc-immersion method is considered to be the most satisfactory and practical for plating substantially all of the different aluminum alloys with various other metals.

Nature of Aluminum 2. (a) Microstructure.-It has been difficult to find a preplating procedure that will be equally satisfactory for all types and tempers of aluminum alloys because the various alloys and products behave diffel'ently electrochemically since they have different metallurgical structures. When elements are added for alloying purposes, they may appear in an aluminum alloy in several different forms; tllat is, tlley may 1 Under the standardization procedure of the Society, this recommended practice is under the jurisdiction of the ASTM Committee B-8 on Electrodeposited Metallic Coatings. 2 Prior to adoption, this recommended practice was published as tentative from 1951 to 1953.

be in solid solution in the aluminum lattice, be present as micro-particles of the elements themselves, or be present as particles of intermetallic compounds formed by combination with the aluminum. The several solid solution matrices and the twenty or more microconstituents that may occur in commercial alloys may have different chemical and electrochemical reactivities and their smfaces may not respond uniformly to various chemical and elech'ochemical treatments. In addition, the response may be influenced by variations in the microstructure of different lots or products of the same alloy. The plater should know, if possible, the type of aluminum alloy that is to be plated in order to select the best plating procedure. (b) Oxide Film.-In addition to differences in microstructure that may affect response to preplating conditioning h'eatments, all aluminum products have an ever-present natural oxide film. This oxide film can be removed by various acid and alkaline treatments, but after rinsing the surface will still have an oxide film that re-formed during tlle treatment. For best results with the zinc-immersion process, the new oxide film should be thinner and more unifonn and provide a suitable smface for deposition of the zinc-immersion layer.

Cleaning and Conditioning Treatments 3. (a) To obtain consistent results with the zincimmersion process for plating aluminum alloys, it is essential that the various cleaning and conditioning treatments provide a smface of uniform activity for the deposition of the zinc layer. First, the surface should be free of any oil, grease, or other foreign material. For removing oil or grease, vapor degreasing or solvent cleaning may be necessary. Ordinarily, a mild etching-type alkaline cleaner is recommended. One can be made conveniently by using 23 g per I (3 oz per gal) each of sodium carbonate and trisodium phosphate. This solution should be used at a temperature of 140 to 180 F (60 to 82 C) for 1 to 3 min. 155


Preparation of and Plating on Aluminum Alloys (B 253 . 53) (b) After appropriate cleaning, further treatment Zinc Immersion of the surface is generally required. For this conditioning treatment to be effective, it must accomplish two things: (1) remove. the original oxide film; and (2) remove any microconstituents which may interfere with the formation of a continuous zinc-immersion layer or which may react with subsequent plating solutions.

(c) For wrought alloys of the 990 A and MIA types, 3 fairly good conditioning may be obtained by using the carbonate-phosphate cleaner followed by a dip in a nitric acid solution (50 per cent by volume). These alloys do not contain interfering constituents and for some applications this method of conditioning may be ample. (d) One of the more effective conditioning treatments for removing the surface oxide film and any undesirable microconstituents comprises the use of a hot acid etch containing sulfuric acid (15 per cent by volume) fot a period of 2 to 5 min at a temperature of 180 F (82 C). The time of the dip depends upon the alloy involved. Generally the shorter time is used on castings. This treatment is satisfactory for all wrought and most cast aluminum alloys. It not only leaves the surface in an excellent condition for the formation of the zinc-immersion layer, but it also eliminates the undesirable effects of the magnesium-containing constituents in alloys of the GR20A,3 GSllA/' and GSI0N types. (e) Another conditioning treatment which has considerable merit consists of a double zinc-immersion treatment with the first zinc layer being removed by a dip in a nitric acid solution (50 per cent by volume). This treatment has been found to be very effective for use with many cast alloys and with wrought alloys that do not contain appreciable percentages of magnesium and when the identity of the alloy is not known. With this procedure, the first immersion dip removes the original oxide film and replaces it with a zinc layer. Removal of the zinc layer by the nitric acid dip leaves the surface in suitable condition for deposition of the final zinc-immersion layer. (f) For casting alloys containing high percentages of silicon, S12B,5 SC64C,6 SG70A6 and SC84B,5 type alloys, a dip for 3 to 5 sec in a solution containing 3 parts (by volume) of concentrated commercial nitric acid plus 1 part (by volume) of commercial hydrofluoric acid (48 per cent) is recommended for conditioning the surface. • See Tentative Specifications for Aluminum and Aluminum-Alloy Sheet and Plate (ASTM Designation: B 209). 1954 Supplement to Book of ASTM Standards, Part 2. • See Tentative Specifications for Aluminum and Aluminum-Alloy Extruded Bars, Rods, and Shapes (ASTM Designation: B 221), 1954 Supplement to Book of 1\.STM Standards, Part 2. • See Tentative Specifications for Aluminum-Base Alloy Die Castings (ASTM Designation: B 85), 1954 Supplement to Book of ASTM Standards, Part 2. . • See Standard Specifications for Aluminum-Base Alloys in Ingot Form for Sand Castings, Die Castings, and Permanent Mold Castings (ASTM Designation: B 179), 1952 Book of ASTM Standards, Part 2.

156

4. (a) In the zinc-immersion step, the oxide film is removed from the surface to be plated and is replaced by a thin and adherent layer of metallic zinc. d f TIllS provides a surface that will respon to most 0 the plating procedures for depositing other metals. (b) For the immersion step, a highly alkaline solution 7 containing the following components is used at room temperature (60 to 80 F; 16 to 27 C): ZINC-IMMERSION SOLUTION

Sodium hydroxide, commercial (76 per cent Na 2 0) 70 oz per gal (525 g per 1) Zinc oxide (Technical Grade) .. 13 oz per gal (100 g perl) The thickness and quality of the immersion coating are influenced by the conditions of deposition. When deposition is too rapid, heavy coarsely crystalline and non-adherent deposits are formed. Since the thinner zinc deposits give the best results, it is recommended that the temperature of the zincate solution be kept below 80 F (27 C) and the immersion time be from 30 sec to 1 min. Recently, a modification of the zincate solution has been developed for wrought and cast alloys, which in most applications gives more uniform and satisfactory results than the standard zinc immersion treatment. The modified zinc immersion procedure 8 has the following advantages: (1) More uniform coverage by subsequent plating baths, (2) Greater operating range for the "Double Immersion" surface conditioning treatment, and (3) Improved resistance to corrosion on all plated aluminum alloys except for the 2024 and 7075 type alloys. The modified solution is prepared by dissolving the zinc oxide in a sodium hydroxide solution in the usual way and cooling to room temperature. Before the bath is diluted to volume, a water solution of ferric chloride crystals and Rochelle Salts is added. The bath should be stirred while the ferric chloride-Rochelle Salts solution is added. The modified zincate solution should be made up as follows: ZINC-IMMERSION SOLUTION

Sodium hydroxide (commercial) (76 per cent Na~O) Zinc oxide Ferric chloride crystals Rochelle salts 7

BATH I

70 oz per gal (525 g per I) 13 oz per gal (100 g per I) 0.13 oz per gal (1.0 g per I) 1.3 oz per gal (10 g per 1)

Proprietary sodium zincate solutions of this general type are available

cOffiluercially.

• The modified zinc immersion procedures described are the subjects of pending patent applications. When a U. S. patent or patents are issued, royalty free licenses will be granted thereunder.


Preparation of and Plating on Aluminum Alloys (B 253 . 53) This bath should also be operated under 80 F (27 C) and for immersion times on the order of 30 sec to 1 min. It is recommended that the modified zincate solution be utilized whenever the "double immersion" conditioning treatment is employed. Likewise, it will be found advantageous on all wrought and cast alloys, excepting of course the 2024 and 7075 types for corrosion-resistant applications. Another variation of the modified zinc immersion procedure 9 has been developed for applications where the rinsing and drag-out are problems. This variation consists of reducing the bath viscosity by lowering the concentration of the principal components. At the same time, a low coating weight must be maintained by a closer control of operating conditions and by addition agents. Two typical dilute baths, which may be prepared in the usual manner, are as follows: ZINc-IMMERSION SOLUTION

Sodium hydroxide Zinc oxide Rochelle salts Ferric chloride crystals Sodium nitrate ZINC-IMMERSION SOLUTION

Sodium hydroxide Zinc oxide Rochelle salts Ferric chloride crystals Sodium nitrate

BATH II

6.7 oz per gal (50 0.67 oz per gal (5 6.7 oz per gal (50 0.27 oz per gal (2 0.13 oz per gal (1

g per g per g per g per g per

1) 1) 1) 1) I)

BATH III

16.0 oz per gal (120 g per I) 2.7 oz per gal (20 g per 1) 6.7 oz per gal (50 g per 1) 0.27 oz per gal (2 g per 1) 0.13 oz per gal (1 g per 1)

Bath III will provide a greater zinc reserve for high production work with only a small sacrifice in rinsing and drag-out properties. When using these dilute solutions, the temperature must be maintained at 70 to 75 F (21 to 24 C) and the immersion time must not exceed 30 sec. ( c) The zincate solution is very viscous and losses occur largely from drag-out. This is advantageous as it limits the accumulation of impurities resulting from attack on the aluminum. (d) The specific gravity of the solution should be checked occasionally and any loss made up by adding more of the components. Loss of volume by drag-out should be corrected by the addition of more solution of the specified composition. ( e) When a properly conditioned aluminum alloy article is immersed in the zincate solution, the thin natural oxide film that is present on the sUlface of the alticle dissolves and, as soon as any underlying aluminum is exposed, it also starts to dissolve and is imme• The modified zinc immersion procedures described are the subjects of pending patent applications. When a U. S. patent or patents are issued, royalty free licenses will be granted thereunder.

diately replaced by an equivalent weight of zinc. When the aluminum surface is completely covered with an extremely thin layer of zinc, action in this solution virtually ceases. (f) With correct procedure, the resulting zinc deposit will be fairly uniform and firmly adherent to the surface. The appearance of the surface, however, will vary with the alloy being coated as well as with the rate at which the coating forms. The weight of zinc deposit should be of the order of 0.1 to 0.3 mg per sq in. (0.016 to 0.048 mg per sq cm) (0.02 to 0.07 p.. in thickness). Generally, it is desirable to limit the weight of the deposit to not over 0.2 mg per sq in. (0.03 mg per sq em). ( g) The thinner and more uniform zinc deposits are the most suitable for plating preparation and for the performance of plated coatings in service. Heavy zinc deposits tend to be spongy and less adherent and do not provide as good a surface for obtaining adherence as the thimler deposits. The weight of zinc deposit will vary with the alloy and the conditioning treatment that is used.

Plating Aluminum Alloys 5. (a) After the surface of an aluminum alloy article has been conditioned and the zinc-immersion deposit has been formed, other metals can be plated on this surface by any of the methods suitable for plating on zinc. One factor, however, must be taken into consideration; that is, the zinc deposit is extremely thin and any plating treatment that penetrates the zinc layer and attacks the underlying aluminum will result in a poor deposit. ( b) Ordinarily, it is advisable to apply a suitable copper strike over the zinc-immersion layer before· other metals are deposited. Silver, brass, zinc, nickel, or chromium, however, may be deposited on the zincimmersion layer provided the plating procedures are suitable for plating over zinc.

Copper Strike 6. (a) For applying a copper strike prior to plating with other metals, a Rochelle-type copper cyanide solution of the following composition is recommended: ROCHELLE-TYPE COPPER STRIKE SOLUTION

Copper cyanide Total sodium cyanide Sodium carbonate Rochelle salts Free sodium cyanide, max

5.5 oz per gal (41.3 6.5 oz per gal (48.8 4.0 oz per gal (30.0 8.0 oz per gal (60.0 0.5 oz per gal ( 3.8

g perl) g per I) g per I) g per I) g per I) 157


Preparation of and Plating on Aluminum Alloys (B 253 . 53) ( b) This sh-ike solution is generally employed at 100 to 130 F (38 to 54 C) and pH of 10.2 to 10.5. Electrical contact should be made before the article is immersed in the bath and a high initial current density (24 amp per sq ft (2.6 amp per sq dm)) should be used to get rapid coverage. After deposition for about 2 min at this current density, the current may be reduced to 12 amp per sq ft (1.3 amp per sq dm) anQ. deposition continued for an additional 3 to 5 min depending upon thickness desired. A solution of higher pH, such as is sometimes used for copper strikes of this type, will give blistered copper deposits on aluminum alloys, especially on alloys 5052,3 6061,4 and 6063 4 • Mter this strike, the work can be transferred to other standard plating solutions for further plating.

Copper Plating 9. Copper can be applied as a thin deposit on the zinc-immersion layer from the Rochelle-type copper cyanide solution described in Section 6. It is recommended that the thickness be limited to less than 0.3 mil (7.6 f.L), as rough deposits generally occur on high current density areas. By employing a lower current density, the time in this solution may be extended to give heavier deposits, but when a thickness of 0.3 mil (7.6 f.L) has been obtained, it is advisable to transfer the work to one of the proprietary copper plating baths which will plate at a faster rate.

Chromium Plating Brass Plating 7. Brass can be applied from a standard brass plating solution operated at room temperature after the zinc immersion step. A brass plating bath of the following composition is suitable: BRASS PLATING SOLUTION

Copper cyanide Zinc cyanide Sodium cyanide Sodium carbonate Temperature Current density Anodes

3.5 oz per gal (26.3 g per 1) 1.5 oz per gal (11.3 g per 1) 6.0 oz per gal (45.0 g perl) 1.0 oz per gal ( 7.5 g per 1) 80 to 90 F (27 to 32 C) 10 amp per sq ft (1.1 amp per sq elm) 75Cu, 25Zn alloy

10. (a) Chromium may be applied directly to aluminum alloys as a thin deposit (0.02 to 0.05 mil (0.5 to 1.3 f.L) ). It is necessary, however, to first etch the work in a 45 g per 1 (6 oz per gal) sodium hydroxide solution at 150 F (66 C) for sufficient time (1 to 2 min) to develop a slight amount of roughening. Mter water rinsing, the parts should be dipped in a commercial nitric acid solution (50 per cent by volume) for 10 sec, again rinsed, and finally chromium plated in a standard chromium plating bath. A chromium plate applied by this method does not have as good adhesion as one applied over a zinc-immersion coating. The following chromium-plating solution is recommended for use with aluminum alloys: CHROMIUM PLATING SOLUTION

Cadmium Plating' 8. Cadmium may be plated directly on the zincimmersion layer. The use of a strike solution prior to plating is recommended for maximum adhesion. In some cases it may be desirable to apply a nickel coating prior to cadmium plating. Cadmium strike and . cadmium plating baths of the following composition are suitable: CADMIUM STRIKE SOLUTION

Cadmium oxide Sodium cyanide Time Temperature Current density

1.0 oz per gal (7.5 g per 1) 8.0 oz per gal (60 gperl) l min room 25 amp per sq ft (2.7 amp per sq dm)

CADMIUM PLATING SOLUTION

Cadmium oxide .. , Sodium cyanide Brightener Temperature Current density, Anodes 158

3.5 oz per gal (26.3 g per 1) 13.4 02 per gal (100 g per 1) as required room 15 to 45 amp per sq ft (1.6 to 4.8 amp per sq dm) in still tanks cadmium balls

Chromic acid, Cr0 3 • 33 oz per gal (250 g per 1) Sulfate, S04' 0.3302 per gal (2.5 g per 1) Temperature 110 to 115 F (43 to 46 C) CUlTent density 150 amp per sq ft (16 amp per sq dm)

( b) When the chromium is applied over the zincimmersion layer, it should be deposited first at a temperature of 65 to 70 F (18 to 21 C). After the initial deposit at low temperahlre, plating can be continued at a high temperahu'e. The transition from low to high temperature can be accomplished by heating the .chromium plating bath after the low temperahlre plate has been formed. The work can also be transferred without rinsing from a cold to a high temperature bath. The work should be held in the hightemperature solution, without current however, until it reaches the temperature of the bath. Plating is then started at 150 amp per sq ft (16 amp per sq dm) and the current should be raised gradually to 300 or more amp per sq ft (32 amp per sq dm). (c) Bright decorative chromium deposits can be applied to aluminum alloys in the conventional manner, that is, the surface plated with copper and then with the required thickness of nickel. Mter nickel


Preparation of and Plating on Aluminum Alloys (B 253.53) plating, the surface should be buffed before applying the chromium deposit. When a bright nickel is used, the chromium deposit can be applied directly. Standard recommendations regarding rinsing and activating the nickel surface should be followed. ( d) Another method for producing chromium deposits having a bright metallic luster consists in applying a 5 to 10-min deposit from a low-temperature solution (65 to 70 F; 18 to 21 C) directly over the zincimmersion layer. The deposit produced in this manner is slate gray, but may be buffed to an attractive metallic luster by using special chrome buffing compounds. This method can be used for applications requiring an inexpensive bright chromium finish. Surfaces finished in this manner will not smudge and are suitable for applications where corrosive conditions will not be encountered. The chromium layer is very thin, however, and will not be nearly as resistant to abrasion and mechanical damage as the copper-nickel-chromium system usually employed for decorative applications.

( e) Heavy, hard chromium deposits can be applied to aluminum alloys by plating the chromium from a high-temperature (130 F (54 C )) chromiumplating solution at a current density of 150 amp per sq ft (16 amp per sq dm) depending upon the racking, contour of work and thickness of plating. The work must first be given a 3 to 5-min strike in the Rochelletype copper cyanide solution, then rinsed and finally transferred to the hot chromium-plating solution for application of hard chromium to the desired thickness.

(f) Hard chromium plates may also be deposited directly over the zinc-immersion layer when the initial deposit is formed from a chromium-plating bath operated in the range of 65 to 70 F (18 to 21 C). After application of the initial chromium deposit at the low temperature, plating is continued in a bath operated at 130 F (54 C). The work should be held in the latter bath until it reaches the temperature of the bath before the current is applied. Plating should be started at 150 amp per sq ft (16 amp per sq dm) and the current should be raised gradually to 300 amp per sq ft (32 amp per sq dm) depending on the shape of the article, method of racking, etc.

Gold Plating 11. Gold may be plated on aluminum alloys by first applying a strike in the Rochelle-type copper cyanide solution or in a brass-plating solution. After this, a suitable deposit of nickel should be applied before application of the gold. The plating bath and conditions for gold plating are as follows:

GOLD PLATING SOLUTION Potassium gold cyanide .. lh ozpergal (3.8gperl) Potassium carbonate 1 oz per gal (7.5 g perl) Potassium cyanid~ lh ozper gal (3.8 gperl) Temperature 120 to 160 F (49 to 71 C) CUlTent density 5 to 15 amp per sq ft (0.5 to 1.6 amp per sq dm) Voltage 2 to 6 v Anodes Chromium-nickel steel or carbon, or combinations of these with gold.

Nickel Plating 12. (a) Nickel may be applied directly over the zinc-immersion layer by using baths formulated for plating over zinc. This method, however, is difficult to control and satisfactory adhesion is not always obtained. Where dull or bright nickel is to be applied, it is preferable to do it after a thin copper plate has been deposited from the Rochelle-type copper cyanide strike solution. For the nickel plating of aluminum alloys, subsequent to copper plating, the following types of nickel baths are suitable: WATTS' TYPE NICKEL SOLUTION (DULL NICKEL) Nickel sulfate crystals. 30 oz per gal (225 g per I) Nickel chloride 6 oz per gal (48 g per I) Boric acid 5 ozper gal (31.5 gperl) pH : 5.0 Temperature. " 130 to 140 F (54 to 60 C) Current density 40 amp per sq ft (4.3 amp per sq dm) BRIGHT NICKEL SOLUTIONS Bright nickel solutions are satisfactory for use with aluminum alloys. Use brightening agents and operating conditions recommended by vendor.

( b) When nickel plating aluminum alloys, all the precautions usually recommended should be followed for obtaining a sound nickel plate-frequent carbon treatment, continuous purification, and filh'ation-to keep the nickel bath in good operating condition. Because of the large elech'olytic potential between nickel and aluminum alloys, the nickel plate should be of good quality and of sufficient thickness to provide adequate protection for the application at hand. ( c) For applications where corrosion is not a critical factor, nickel plate of the order of 0.3 to 0.5 mil (8 to 13 p.) in thickness will be satisfactory. Where corrosive conditions. may be encountered in service, however, the nickel plate should be from 1 to 2 mil (25 to 50 p.) in thickness. In addition, the application of a final chromium plate 0.01 to 0.02 mil (0.25 to 0.50 p.) in thickness is essential, as it will increase the 159


Preparation of and Plating on Aluminum Alloys (B 253- 53) service life of a plat~d aluminum article to a surprising degree and will greatly reduce the detrimental effects of pores and exposed areas of bare metal.

(d) Ordinarily, nickel plating by itself is not recommended for use on aluminum alloys when even moderately corrosive conditions are likely to be encountered in service. When relatively heavy nickel deposits are applied to obtain protection, a ductile type of nickel plate should be used and plating baths or operating conditions that produce highly stressed deposits should be avoided. With highly stressed deposits, stress cracks may develop on exposure and blistering and spalling of the plating will occur.

posits can be formed on aluminum from hot sodium stannate solutions.

Zinc Plating 15. Zinc can be plated over the zinc-immersion layer from either acid or cyanide solutions at room temperature. The current, however, should be applied as the work is immersed in the plating solution. Zinc can also be applied directly to aluminum alloys without employing the zinc-immersion dip, but operating conditions are too critical for production use. A zinc plating bath of the following composition is suitable: ZINC PLATING SOLUTION

Silver Plating 13. Silver can be deposited on the zinc-immersion

coating by following the silver plating procedure employed for steel. This involves the use of two preliminary strikes and making contact before the work enters the solution. It is better, however, to apply silver over a copper plate without using the first silver strike. The following solutions may be used:

Zinc cyanide Sodium cyanide Sodium hydroxide Temperature " Current density

8.0 oz per gal (60 g perl) 5.6 oz per gal (42 gperl) 10.5 ozper gal (78.8 g perl) 75 to 95 F (24 to 35 C) 5 to 50 amp per sq ft (0.54 to 5.4

amp per sq dm)

Racking FIRST SILVER STRIKE SOLUTION

Silver cyanide Sodium cyanide Temperature Current density Tank voltage Time

0.13 oz per gal (1 g per 1) 12 oz per gal (90 g per 1) 80 F (27 C) 15 to 25 amp per sq ft (1.6 to 2.7 amp per sq dm) 6v 10 sec

SECOND SILVER STRIKE SOLUTION

Silver cyanide Sodium cyanide Temperature Current density Tank voltage Time

0.7 oz per gal (5.3 g perl) 9 oz per gal (67.5 g per 1) 80 F (27 C) 15 to 25 amp per'sq ft (1. 6 to 2.7 amp per sq dm) 6v 10 sec

16. (a) Aluminum racks are preferred when plating aluminum alloys. It is recommended that 990 A alloy be used for the spines of the racks and CG42A alloy for the contacts. By increasing the cross-sectional area of the spines by about 40 per cent, a conductance equal to that of a copper rack is obtained. In cases where contact marks are not important, regular phosphor-bronze contacts may be used. When using phosphor-bronze contacts, however, the area adjacent to the contact may develop small blisters as a result of a non-uniform zinc deposit during the immersion step. Aluminum alloy contacts will eliminate this condition and their use is recommended when contact marks would be on an exposed surface of the article being plated. When the nitric-hydrofluoric acid etch is used for conditioning, aluminum contacts should be used.

SILVER PLATING SOLUTION

Silver cyanide .4 oz per gal (30 g perl) Potassium cyanide (total) .. 7.4 ozper gal (55.5 gperl) Potassium carbonate 6 oz per gal (45 g per 1) Free potassium cyanide 5.5 oz per gal (41.3 g per 1) Temperature 80 F (27 C) 5 amp per sq ft (0.54 amp per Current density sqdm)

Tin Plating 14. Tin can be plated on a surface that has a zincimmersion coating and a copper strike. Either a stannate or a fluoborate-type tin plating solution can be used. For some applications, useful tin immersion de160

(b) When aluminum alloys are used for the plating racks,. the various electrodeposits may be stripped from these racks by reversed current treatment in a sulfuric acid solution (60 per cent by volume) or a phosphoric acid solution (75 per cent by volume) at room temperature. In either case, only slight attack occurs on the aluminum because of the oxide film that forms on the aluminum during these anodic treatments. The oxide film resulting from this stripping operation should be removed from contact areas either chemically or mechanically. When phosphor-bronze contacts are used, it is recommended that they be stripped in the sulfuric acid solution (60 per cent by volume).


Preparation of and Plating on Aluminum Alloys (B 253 . 53) Rinsing 17. (a) Effective rinses should follow eveq step in the plating procedure. The rinses must be reasonably clean and the rinsing thorough to prevent contamination of succeeding solutions. A combination of dip and spray rinsing has been found to use the least

water for good rinsing. Since th~ zinc-immersion solution is rather viscous, the subsequent rinsing operation is veq important. A double rinse is needed to remove all traces of the zincate solution. Two combination "dip and spray" rinses are desirable. Water from the second dip rinse can be made to overflow into the first dip rinse, thereby effecting an economy.

Appendix Cleaning and Conditioning Summary of Cleaning and Conditioning T1'eatments: AI. The following cleaning and conditioning treatments are suitable for the wrought and cast aluminum alloys covered by this recommended practice: Treatment A: (1) Clean: (a) By vapor degreasing or with mineral spirits. (b) With alkaline cleaner and water rinse. (2) Acid dip, in nitric acid solution (50 per cent by volume). (3) Water rinse. (4) Zinc-immersion dip, ~ to 1 min at 60 to 80 F (16 to 27 C). (5) Double water rinse. ( 6) Electroplate. Treatment B: (1) Clean: (a) By vapor degreasing or with mineral spirits. . (b) With alkaline cleaner and water rinse. (2) Acid dip, in sulfuric acid solution (15 per cent volume), 2 to 5 min at 180 F. (3) Water rinse. (4) Acid dip, in nitric acid solution (50 per cent by volume) at room temperature. (5) Water rinse. (6) Zinc-immersion dip, ~ to 1 min at 60 to 80 F (16 to 27 C). ( 7) Double water rinse. ( 8) Electroplate. T1'eatment C: (1) Clean: (a) By vapor degreasing or with mineral spirits. ( b) With mild alkaline cleaner and water rinse. (2) Zinc-immersion dip, ~ to 1 min at 60 to 80 F (16 to 27 C).

( 3) Water rinse. ( 4) Acid dip, in nitric acid solution (50 per cent by volume) at room temperature. (5) Water rinse. (6) Zinc-immersion dip, ~ to 1 min at 60 to 80 F (16 to 27 C). (7) Double water rinse. ( 8) Electroplate. Treatment D: (1) Clean: ( a) By vapor degreasing or with mineral spirits. ( b) With mild etching alkaline cleaner and water rinse. (2) Mixed acid dip (nitric-hydrofluoric at room temperature, 3 to 5 sec).

TABLE I.-CLEANING AND CONDITIONING TREATMENTS. Alloy

*

Treatments Suitable

Wrought Aluminum Alloys: 990A MIA , MGllA CP60A CM41A CG42A GR20A GSllB GSllA Cast Aluminum Alloys: S5 S5B SC2 CS43A C272B CS40A SC64C . . . . . . . . . . . . . . . . . . . . . . . . . . .. SC51A SG70A SC7 '"

A,B,C A,B,C B,C B, C B, C B,C B,C B, C B, C C,D C B, C B, C B B, C B, C, D B, C C, D D

* See page 141 for Alum. Assoc. designations. 161


Preparation of and Plating on Aluminum Alloys (B 253 . 53) (3) Water rinse. (4) Zinc-immersion dip, ;f to 1 min at 60 to 80 F (16 to 27 C). (5) Double water rinse. (6) Electroplate. The treatments applicable to specific alloys are shown in Table 1.

Solutions fo1' Cleaning and Conditioning Aluminum Alloys: A2. The solutions described in Paragraphs (a) to (f) are suitable for cleaning and conditioning aluminum alloys. (a) CARBONATE-PHOSPHATE Sodium carbonate Trisodium phosphate Temperature Time Container ( b) SULFURIC ACID DIP: Sulfuric acid (H2S0.( 66 deg Baume) Water TemperahIre Time Container

CLEANER: 3 oz per gal (23 g per 1) 3 oz per gal (23 g per 1) 140 to 180 F (60 to 82 C) 1 to 3 min steel

1.5 vol 8.5 vol 175 to 180 F (79 to 82 C) 5nlin lead-lined steel

( c) NITRIC ACID DIP: Commercial nitric acid (sp gr 1.37) Water Temperature Container

1 vol 1 vol room steel lined with type 347 stainless steel NOTE: Catttion.-Exhaust fmnes are toxic.

(d) MIXED ACID DIP: Commercial nitric acid (sp gr 1.42) Commercial hydrofluoric acid (48 per cent) Time Temperature Container

162

3 vol 1 vol 3 to 5 sec room steel, lined with a suitable plastic lining, such as Koroseal or car-

bon brick; preferably a combination of both. NOTE: Catttion.-Exhaust fumes are toxic. (e) STANDARD ZINC-IMMERSION SOLUTION: Sodium hydroxide 70 oz per gal (525 g per 1) Zinc oxide 13 oz per gal ( 100 g per 1) Time V2 to 1 min Temperature 60 to 80 F (16 to 27 C) Container steel

MODIFIED ZINC IMMERSION SOLUTIONS: I Sodium hydroxide (commercial) (76 per cent Na20) 70 oz per gal (525 g perl) Zinc oxide 13 oz per gal ( 100 g perl) Ferric chloride crystals .. 0.13 oz per gal (1.0 g per 1) Rochelle salts 1.3 oz per gal (lOg perl) Time V2 to 1 min. Temperature 60 to 80 F (16 to 27 C) Container steel II Sodium hydroxide 6.7 oz per gal (50 g per 1) Zinc oxide 0.67 oz per gal (5 g perl) Rochelle salts 6.7 oz per gal (50 g per 1) Ferric chloride clystals .. 0.27 oz per gal (2 g per 1) Sodimn nitrate 0.13 oz per gal (1 g per 1) Time 30 sec. or less 70 to 75 F (21 to 24 C) Temperature Container steel III Sodium hydroxide 16.0 oz per gal (120 g per 1) Zinc oxide 2.7 oz per gal (20 g perl; Rochelle salts 6.7 oz per gal (50 g per 1) Ferric chloride crystals .. 0.27 oz per gal (2 g per 1) Sodium nitrate 0.13 oz per gal (1 g perl) Time , 30 sec. or less Temperahrre 70 to 75 F (21 to 24 C) Container steel

(f) CAUSTIC DIP: Sodium hydroxide Time Temperature Container NOTE: Caution.-Exhaust

6 oz per gal (45 g per 1) 10 sec 150 F ( 66 C) steel fumes are toxic.

STANDARD SPECIFICATIONS FOR ELECTRODEPOSITED COATINGS OF ZINC ON STEEL

1

ASTM DESIGNATION: A 164· 55 Adopted, 1953; Revised, 1955. 2 This Standard of the American Society for Testing Materials is issued under the fixed designation A 164; the final number indicates the year of original adoption as standard or, in the case of revision, the year of last revision.

These specifications were prepared faintly by the American Electmplated Society, the National BU1'eau of Standards, and the American Society for Testing Materials.

Scope 1. These specifications cover requirements for electroplated zinc coatings on steel articles that are required to withstand corrosion. Three types of coatings (Notes 1 and 2) are covered: namely,

Type GS, Type LS, and TypeRS. NOTE 1: Explanation of Symbols.-The initial letters, G, L, and R were adopted as arbib:ary designations of grades of plating. The second letter S refers to steel as the basis metal; other basis metals are indicated by the letters B for brass, C for copper, and Z for zinc. NOTE 2: Classification.-The conditions of exposure and use of plated steel are so varied that it is not possible to predict the average life of articles plated in accordance with type GS, type LS, or type RS, or to predetermine just which type of plating should be specified for a given article. Such a selection must be based upon the experience of the manufacturers and users. It is recognized that uses exist for which thicker coatings than those of type GS will be required. For articles that are intended for a short period of use, no standard specification for plating is recommended. It is suggested, however, that subject to the prevailing manufactming conditions, certain minimum requirements be mutually agreed upon by the manufacturer and the purchaser in order to insure that the plated coatings render a useful service.

Manufacture 2. The steel to be plated shall be substantially free from flaws or defects that will be detrimental to the appearance or the protective value of the coatings. It shall be subjected to such cleaning, pickling, and plating procedures as are necessary to yield deposits with 1 Under the standardization procedure of the ASTM, these specifications are under the jurisdiction of the ASTM Committee B-8 on Electrodeposited Metallic Coatings. 2 Prior to adoption as standard, these specifications were published as tentative from 1935 to 1953, being revised in 1939, 1940, 1949 and 1951.

the desired quality. The zinc coating shall have a uniform appearance, shall be adherent and free from blisters, and substantially free from other defects that may affect the appearance or protective value of the coatings.

Minimum Thickness of Coating 3. (a) Type GS .-On significant surfaces of the finished articles the minimum thickness of type GS zinc coating shall be 0.0010 in. (25j.L).

(b) Type LS .-On significant smfaces of the finished articles, the minimum thickness of type LS zinc coating shall be 0.00050 in. (13j.L). (c) Type RS .-On significant smfaces of the finished articles, the minimum thickness of type RS zinc coating shall be 0.00015 in. (3.8j.L). NOTE.-l

p. (micron) = 0.0000394 in.

0.001 in.

= 1 mil = 25p. (microns).

2.-See Appendix II. NOTE 3.-The performance of a zinc coating depends largely on its thickness and the kind of environment to which it is exposed. Without proof of satisfactory cOlTelation, accelerated tests, such as the salt spray test, cannot be relied upon to predict performance in other environments, nor will these serve as comparative measures of the con-osion protection afforded by coatings of different metals. Thus the marked superiority shown by cadmium coatings over zinc coatings of equal thickness in the standard salt spray test cannot be conshlled as proof that this will hold h'ue in all ahnospheric environments. NOTE

Significant Surfaces 4. In general, significant smfaces (Note) are those surfaces that are visible and subject to wear or corrosion or both, or surfaces on which the coating is otherwise fl.U1ctionally necessary. The designation of significant surfaces shall be agreed upon by the manufacturer 163


Specifications for Electrodeposited Zinc (A 164 . 55) and the purchaser and may be indicated on the drawings. Surfaces on which a controlled deposit ordinarily cannot be obtained, such as holes, recesses, bases of angles, and similar areas, are normally exempt from the requirements for significant surfaces, unless they are specifically designated as such. When such areas are designated as significant surfaces, and the thickness requirements must be met, the manufacturer and the purchaser shall recognize the necessity for either thicker deposits on the more accessible surfaces or for special racking. Special racks may involve the use of conforming, auxiliary,·· interior, or bi-polar electrodes. NOTE.-It is suggested that significant surfaces generally may be defined as those parts of the visible surface that can be touched with a %-in. diameter sphere or with a sphere of a diameter agreed upon by the manufacturer and the purchaser.

Hydrogen Emhrittlement 5. Mter plating and any necessary subsequent operations (Note) the steel shall be free from the detrimental effects of hydrogen embrittlement. The test methods and their evaluation for freedom from hydrogen embrittlement shall be agreed upon by the manufacturer and the purchaser. NOTE.-Hardened steels and cold-worked steels are susceptible to embrittlement by hydrogen in both cleaning and plating operations. This embrittlement should be minimized to the greatest possible extent by careful control of these operations. Embrittlement unavoidably present after plating should be removed by a subsequent treatment such as baking. A procedure for baking to minimize embrittlement is covered in Sections 2 ( b) and 7 of the Recommended Practice for the Preparation of High-Carbon Steel for Electroplating (ASTM Designation: B 242).

Test for Thickness of Coating 8. (a) All the samples selected may be tested by the purchaser to determine the minimum thickness of coating on significant surfaces. Unless otherwise agreed upon by the manufacturer and the purchaser, the thiclmess of coating shall be determined on crosssections taken perpendicular to the significant surfaces by the microscopic method described in the Methods of Test for Local Thickness of Electrodeposited Coatings (ASTM Designation: A 219). NOTE.-It is advisable to determine thickness of coating on large or irregularly shaped parts at several points.

( b) Unless otherwise agreed upon by the manufacturer and the purchaser, measurements of the thickness of coating on threaded articles, such as nuts, bolts, screws and similar fasteners with complementary threads, shall be made on the shank or other smooth surfaces as nearly adjacent to the thread as practicable. ( c) When agreed upon by the manufacturer and the purchaser, the thickness of a zinc coating directly on steel may be determined by the magnetic method described in Appendix I or by the dropping test described in Appendix II of the Methods of Test for Local Thickness of Electrodeposited Coatings (ASTM Designation: A 219).

Acceptance and Rejection 9. (a) The number of samples permitted to fail in the tests, the number of samples which shall be taken for retest when the first are indecisive, and the number of samples that may fail in the retest shall be agreed upon by the manufacturer and the purchaser.

( b) The purchaser shall notify the manufacturer of the rejection of any lot within two weeks of receipt of shipment.

Selection of Samples

Retest

6. Out of a lot of similar pads, a number of samples shall be selected at random. The size of the lot and the number of samples to be selected shall be agreed upon by the manufacturer and the purchaser. All of the samples selected shall be visually examined for any defects as described in Section 2.

10. Disagreements shall be settled by an umpire test made by an independent laboratory agreed upon in advance by the manufacturer and the purchaser.

Number of Tests 7. All of the samples shall be tested for thickness of coating in accordance with Section 8. NOTE.-Wherever possible, thicknesses should be measured by magnetic methods on the maximum number of samples practicable since such measurements are nondestructive and inexpensive.

164

Cost of Tests 11. (a) The purchaser shall pay for his own tests. He shall not be required to pay for specimens destroyed in testing lots that are rejected. The cost of umpire tests shall be paid by the loser.

( b) When the contract involves only the plating of pads, the plating firm shall be permitted to destroy, without cost to it, for testing purposes, twice the number of parts agreed upon in accordance with Sections 6,9, and 10.


Specifications for Electrodeposited Zinc (A 164 . 55) Appendix I Control: In order to meet the specifications the manufacturer is advised to: ( a) Maintain regular control of all solutions and inspect the equipment at regular intervals, paying special attention to electrical contacts and accuracy of instruments. ( b) Maintain his own inspection department, using the test methods called for in these specifications, and to trace immediately the source of irregularities. On jobs running continuously over any length of time, the quality of the coatings on each part should be checked at least twice every shift, after initial difficulties have been- overcome. (c) Maintain his own requirements at least 10 per cent above those of the specifications. Time Required for Plating: Any specified thickness of plating can be produced consistently only if the current density and time of plating are controlled. Regulation of the voltage is of no value except so far as it produces the desired current density. The average thickness of deposit that is required to produce a specified minimum thickness of deposit will depend upon the shape of the article, the shape

and position of the anodes, and the throwing power of the solution. Purely for illustration, it will be assumed that the average thickness will be 50 per cent greater than the mininmm thickness. The resultant figures serve only as a rough guide and must be confinned by trial for the articles concerned. To deposit 0.0010 in. (25p.) of zinc with high efficiency in either acid or cyanide baths, it requires about 14 amp hr per sq ft. To produce an average thickness of 0.0015 in. (38p.) (that is, 50 per cent more than the minimum thickness of 0.0010 in. (25JL) specified for type GS), it will therefore require about 21 amp hr per sq ft. This is equivalent to plating for 1 hr at 21 amp per sq ft, or to a corresponding period for any other current density. Similarly, for type LS it will re~ quire about 11 amp hr per sq ft and for type RS about 3.5 amp hr per sq ft to deposit an average thickness about 50 per cent greater than the specified minimum thickness. For complicated shapes, longer periods will be required. When a large number of small articles are plated simultaneously (for example, on a rack or in a barrel), the time of plating must be increased to insure the specified thickness on those articles that receive less than the average current density.

Appendix II Coating Thickness on Threaded Articles with Complementary Threads

The dimensional tolerance of most threaded articles, such as nuts, bolts, screws and similar fasteners with complementary threads, nonnally does not permit the application of coating thickness much greater than Type RS. The limitation of coating thickness on threaded fasteners imposed by dimensional tolerances (including class or fit) should be a subject for con-

sideration wherever practicable, both by the manufacturer and by the purchaser, to prevent the application of greater coating thicknesses than are generally permissible. If heavier coatings are required for satisfactory corrosion resistance, allowances must be made in the manufacture of the threaded fasteners for the tolerance necessary for plate build-up.

165

STANDARD SPECIFICATIONS FOR ELECTRODEPOSITED COATINGS OF CADMIUM ON STEELl ASTM DESIGNATION: A 165 . 55 Adopted, 1953; Revised, 1955. 2 This Standard of the American Society for Testing Materials is issued under the fixed designation A 165; the final number indicates the year of original adoption as standard or, in the case of revision, the year of last revision.

These Specifications were prepared faintly by the American Electroplaters' Society, the Natwnal Bureau of Standards, and the American Society for Testing Materials.

Scope 1. These specifications cover requirements for elech'oplated cadmium coatings on steel articles that are required to withstand corrosion. Three types of coating (Notes 1 and 2) are covered: namely,

Type NS, Type O~, and Type TS. NOTE 1: Explanation of Symbols.-The initial letters N, 0, and T were adopted as arbitrary designations of grades of plating. The second letter S refers to steel as the basis metal; other basis metals are indicated by the letters B for brass, C for copper, and Z for zinc. NOTE 2: Classification.-The conditions of exposure and use of plated steel are so varied that it is not possible to predict the average life of articles plated in accordance with type NS, type OS, or type TS, or to predetermine just which type of plating should be specified for a given article. Such a selection must be based upon the experience of the manufacturers and users. It is recognized that uses exist for which thicker coatings than those of type NS will be required. _ For articles that are intended for a short period of use, no standard specification for plating is recommended. It is suggested, however, that subject to the prevailing manufacturing conditions, certain minimum requirements be mutually agreed upon by the manufacturer and the purchaser in order to insure that the plated coatings render a useful service.

be adherent and free from blisters, and substantially free from other defects that may affect the appearance or protective value of the coatings.

Minimum Thickness of Coating 3. (a) Type NS.-On significant surfaces of the finished articles, the minimum thickness of type NS cadmium coating shall be 0.00050 in. (13,u.).

(b) Type OS.-On significant surfaces of the finished articles, the minimum thickness of type as cadmium coating shall be 0.00030 in. (7.6,u.). (c) Type TS.-On significant surfaces of the finished articles, the minimum thickness of type TS cadmium coating shall be 0.00015 in. (3.8,u.). NOTE 1.-11£ (micron) 0.0000394 in. 0.001 in. 1 mil 251£ (microns). NOTE 2.-See Appendix II. NOTE 3.-The performance of a cadmium coating depends largely on its thickness and the kind of environment to which it is exposed. Without proof of satisfactory correlation, accelerated tests, such as the salt spray test, can not be relied upon to predict performance in other environments, nor will these serve as comparative measures of the corrosion protection afforded by coatings of different metals. Thus the marked superiority shown by cadmium coatings over zinc coatings of equal thickness in the standard salt spray test cannot be construed as proof that this will hold true in all atmospheric environments.

=

=

=

Manufacture 2. The steel to be plated shall be substantially free from flaws or defects that will be deh'imental to the appearance or the protective value of the coatings. It shall be subjected to such cleaning, pickling, and plating procedures as are necessary to yield deposits with the desired quality. The cadmium coating shall have a uniform appearance, bright or dull as specified, shall 1 Under the standardization procedure of the ASTM, these specifications are under the jurisdiction of the ASTM Committee B-8 on Electrodeposited Metallic Coatings. 2 Prior to adoption as standard, these specillcations were published as tentative from 1935 to 1953, being revised in 1939, 1940, 1949 and 1951.

166

Significant Surfaces 4. In general, significant surfaces (Note) are those surfaces that are visible and subject to wear or corrosion or both, or surfaces on which the coating is otherwise functionally necessary. The designation of significant surfaces shall be agreed upon by the manufacturer and purchaser and may be indicated on the drawings. Surfaces on which a controlled deposit ordinarily cannot be obtained, such as holes, recesses, bases of angles, and similar areas, are normally exempt


Specifications for Electrodeposited Cadmium (A 165 . 55) from the requirements for significant surfaces, unless they are spec~fically desig~at.ed as such. When such areas are desIgnated as slgmficant surfaces, and the thickness requirements must be met, the manufacturer and the purchaser shall recognize the necessity for either thicker deposits on the more accessible smfaces or for special racking. Special racks may involve the use of conforming, auxiliary, interior, or bi-polar . electrodes. NOTE.-It is suggested that significant surfaces generally may be defined as those parts of the visible surface that can be touched with a %-in. diameter sphere or with a sphere of a diameter agreed upon by the manufacturer and the purchaser.

Hydrogen Embrittlement 5. Mter plating and any necessary subsequent operations (Note) the steel shall be free from the detrimental effects of hydrogen embrittlement. The test methods and their evaluation for freedom from hydrogenembrittlement shall be agreed upon by the manufacturer and the purchaser. NOTE.-Hardened steels and cold-worked steels are susceptible to embrittlement by hydrogen in both cleaning and plating operations. This embrittlement should be minimized to tlle greatest possible extent by careful control of these operations. Embrittlement unavoidably present after plating should be removed by a subsequent treatment such as baking. A procedure for baking to minimize embrittlement is covered in Sections 2 (b) and 7 of the Recommended Practice for the Preparation of High-Carbon Steel for Elecb.-opIating (ASTM Designation: B 242).

Test for Thickness of Coating 8. (a) All the samples selected may be tested by the purchaser to determine the minimum thickness of coating on significant surfaces. Unless otherwise agreed upon by the manufacturer and the purchaser, the thickness of coating shall be determined on crosssections taken perpendicular to the significant surfaces by the microscopic method described in the Methods of Test for Local Thickness of Electrodeposited Coatings (ASTM Designation: A 219). NOTE.-It is advisable to determine thickness of coating on large or inegularly shaped parts at several points. (b) Unless otherwise agreed upon by the manufacturer and the purchaser, measurements of the thickness of coating on threaded articles, such as nuts, bolts, screws and similar fasteners with complementalY threads, shall be made on the shank or other smooth surfaces as nearly adjapent to the thread as practicable.

( c) When agreed upon by the manufacturer and the purchaser, the thickness of a cadmium coating directly on steel may be determined by tlle magnetic metllod described in Appendix I or by the dropping test described in AppendiX II of the Methods of Test for Local Thickness of Electrodeposited Coatings (ASTM Designation: A 219).

Acceptance and Rejection 9. (a) The number of samples permitted to fail in tlle tests, the number of samples which shall be taken for retest when the first are indecisive, and the number of samples tllat may fail in the retest shall be agreed upon by tlle manufacturer and the purchaser. ( b) The purchaser shall notify tlle manufacturer of tlle rejection of any lot within two weeks of receipt of shipment.

Selection of Samples 6. Out of a lot of similar parts, a number of samples shall be selected at random. The size of the lot and the number of samples to be selected shall be agreed upon by the manufacturer and the purchaser. All of the samples selected shall be visually examined for any defects as described in Section 2.

Retest 10. Disagreements shall be settled by an umpire test made by an independent laboratory agreed upon in advance by the manufacturer and the purchaser.

Cost of Tests Number of Tests 1. All of the samples shall be tested for thickness of coating in accordance with Section 8. NOTE.-Wherever possible, tllicknesses should be measured by magnetic methods on the maximum number of samples practicable since such measurements are nondestructive and inexpensive.

11. (a) The purchaser shall pay for his own tests. He shall not be required to pay for specimens destroyed in testing lots that are rejected. The cost of umpire tests shall be paid by tlle loser.

( b) When the contract involves only tlle plating of parts, the plating firm shall be permitted to destroy, without cost to it, for testing purposes, twice the number of parts agreed upon in accordance with Sections 6,9, and 10.

167


Specifications for Electrodeposited Cadmium (A 165 . 55) Appendix I Control: In order to meet the speci£cations the manufacturer is advised to: (a) Maintain regular control of all solutions and to inspect the equipment at regular intervals, paying special attention to electrical contacts and accuracy of instruments. ( b) Maintain his own inspection department, using the test methods called for in these speci£cations, and to trace immediately the source of irregularities. On jobs mnning continuously over any length of time the quality of the coatings on each part should be checked at least twice every shift, after initial difficulties have been overcome. ( c) Maintain his own requirements at least 10 per cent above those of the speci£cations. Time Required for Plating: Any speci£ed thickness of plating can be produced consistently only if the current density and time of plating are controlled. Regulation of the voltage is of no value except so far as it produces the desired current density. The average thickness of deposit that is required to produce a specified minimum thickness of deposit will depend upon the shape of the article, the shape

and position of the anodes, and the throwing power of the solution. Purely for illustration, it will be assumed that the average thickness will be 50 per cent greater than the minimum thickness. The resultant £gures serve only as a rough guide and must be confirmed by trial for the articles concerned. To deposit 0.0010 in. (250 ) of cadmium with high efficiency, it requires about 10 amp lu' per sq ft. To produce an average thickness of 0.00075 in. (190) (that is, 50 per cent more than the minimum thickness of 0.00050 in. (130) specified for type NS), it will therefore require about 7.5 amp hr (450 amp min) per sq ft. This is equivalent to plating for 1 hr at 7.5 amp per sq ft, or to a corresponding period for any other current density. Similarly, for type OS it will require about 4.5 amp hr per sq ft and for type TS about 2.5 amp hr per sq ft to deposit an average thickness 50 per cent greater than the specified minimum thickness. For complicated shapes, longer periods will be required. When a large number of small articles are plated simultaneously (for example, on a rack or in a barrel), the time of plating must be increased t'O insure the specified thickness on those articles that receive less than the average current density.

Appendix II Coating Thickness on Threaded Articles with Complementary Threads

The dimensional tolerance of most threaded articles, such as nuts, bolts, screws'and similar fasteners with complementary threads, normally does not permit the application of coating thickness much greater than Type TS. The limitation of coating thickness on threaded fasteners imposed by dimensional tolerances (including class or fit) should be a subject for consid-

eration wherever practicable, both by the manufacturer and by the purchaser, to prevent the application of greater coating thicknesses than are generally permissible. If heavier coatings are required for satisfactory corrosion resistance, allowances must be made in the manufacture of the threaded fasteners for the tolerance necessary for plate build-up.

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