initial inspection

TESTING AND COMMISSIONING

8

Initial Inspection Introduction The following notes provide a detailed description of the procedures required to carry out an initial inspection of an electrical installation. Substantial reference has been made to the lEE Wiring Regulations (BS7671), the On Site Guide and lEE Guidance Note No.3 and it is recommended that wherever possible these documents are referred to should clarification be required. As stated previously the most important considerations prior to carrying out any inspection and test procedure is that all the required information is available, the person carrying out the procedure is competent to do so and that all safety requirements have been met. Forward planning is also a major consideration and it is essential that suitable inspection checklists have been prepared and that appropriate certification is available for completion. It is also important to realise that a large proportion of 'any new installation will be hidden from view once the building fabric has been completed and therefore it is preferable to carry out a certain amount of visual inspection throughout the installation process: e.g. conduit, cable tray or trunking is often installed either above the ceiling or below the floor and once the ceiling or floor tiles have been fitted it is difficult and often expensive to gain access for inspection purposes. The same applies to testing and it may be advisable to carry out tests such as earth continuity during construction rather than after the building has been completed. It must be remembered however that when visual inspection and/or tests are carried out during the construction phase, the results must be recorded on the appropriate checklists or test certificates. It is' also worth noting that although the major part of any inspection will be visual other human senses may be employed: e.g. a piece of equipment with moving parts may generate an usual noise if it is not working correctly or an electrical device which overheats. will be hot to touch as well as giving off a distinctive smell. The senses of hearing, touch and smell will assist in detecting these. All these points will be discussed in detail on the following pages.

Information Before carrying out the inspection and test of an installation it is essential that the person carrying out the work be provided with the following information: a) The maximum demand of the installation expressed in amperes per phase together with details of the number and type of live conductors both for the source of energy and for each ciJcuit to be used within the installation, (e.g. single-phase two-wire a.c. or three phase four-wire a.c. etc). b) The general characteristics of the supply . such as : . the nominal voltage(Uo). . the nature of the current (I) and its frequency (Hz). . the prospective short circuit current at the origin of the installation (kA). . the earth fault loop impedance (Ze) of that part of the system external to

the installation.

.

.

the type and rating of the overcurrent device acting at the origin of the installation. If this information is not known it must be established either by calculation, measurement, inquiry or inspection. c) The type of earthing arrangement used for the installation e.g. TN-S, TN-C-S, TT etc. d) The type and composition of each circuit (Le. details of each sub-circuit, what it is feeding, the number and size of condl(ctors and the type of wiring used). e) The location. and description of all devices installed for the purposes of protection, isolation and switching (e.g. fuses/circuit breakers etc). f) Details of the method selected to prevent danger from shock in the event of an earth fault (This will invariably be protection by earthed equipotential bonding and automatic disconnection of the supply.) g) The presence of any sensitive electronic device which may be susceptible to oamage by the application of 500 voits d.c when carrying out insulation resistance tests. The above information may be gained from a variety of sources such as the project specification, contract drawings, as fitted drawings or distribution board schedules. If such documents are not available, then the

the

work

should

be

Questions

the most common form of identification is by means of coloured insulation or sleeving. It should be noted in particular that only protective conductors shall be identified by a combination of the colours green and yellow.

The nominal voltage of a single phase supply to domestic premises in this country

Questions

person ordering approached.

2..3.0....................

is

The nature of tbe current is.A0..and frequency is .5u. H G

its

The colour used to identify t~e neutral conductor of an a.c three phase circuit wired in non-flexible ~able is

.bltJ.L.K~

Scope BS7671 states that as far as reasonably practicable, an inspection shall be carried out to verify that: All equipment and materials used in the installation is of the correct type and complies with the' appropriate British Standards or acceptable equivalent. All parts of the installation. have been correctly selected and installed., No part of the installation is visibly damaged . or otherwise defective. That the installation is suitable for the surrounding environmental conditions.

Question

~~ff.:J£~~...~~~.~:

~~.N3~ ...ur . ':=I~ f"" {}."

~

'~i1S. . . . . . :I.~..~.. . LUA.J.'e-if.t1 11'