Handbook of Electrical Installation Practice - BeKnowledge

INTRODUCTION
CHAPTER 20
Selection of Wiring Systems
R.G. Parr, ACGI, CEng, MIEE
(Consultant)
D.W.M. Latimer, MA(Cantab), CEng, MIEE
(Consulting Electrical Engineer)
Revised by M. Coates, BEng
(ERA Technology)
This chapter deals with the selection of wiring systems for voltages up to and including
1kV. It provides a survey of the more frequently used systems and comments
on the electrical and environmental duties for which each is suitable. Systems for
alarm and control circuits are included.
BS 7671, Requirements for electrical installations (the IEE Wiring Regulations)
requires at clause 512–02–01 that every item of equipment shall be suitable for the
design current and the current likely to flow under abnormal conditions. The term
equipment includes wiring systems. Clause 311–01–01 goes on to say that in determining
the maximum demand of an installation, diversity may be taken into account.
The starting point for selection is an assessment of the load, considering both the
number, location and size of power consuming outlets, required to fulfil the purpose
of the installation, and the total load to be taken from the supply. Guidance on the
determination of maximum demand from connected loads in domestic and commercial
installations is given in the IEE Guidance note No. 1 to BS 7671; the guidance
given is of a general nature and experience of particular types of equipment
and of installations may allow the designer to adopt different values. For industrial
installations, methods used to establish demands differ with the type of industry and
must be based mainly on past experience with particular industrial processes.
Once the expected maximum demand has been determined, a meeting with the
supplier can decide the type of supply, earthing arrangements and the prospective
fault-currents at the origin of the installation. This information will have an important
bearing on the selection of wiring system(s) for the installation.
Division of the installation into circuits and the routing of each circuit are matters
which concerns both safety and convenience.Attention is drawn to the requirements
of BS 7671: Part 3, Assessment of general characteristics, which are relevant at
this stage.
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