16th Edition (reference only) – NOW superseded by the 17th Edition IEE Regulations.

chapter 5

chapter 6

  5.1 - The earthing principle 5.6 - Protective multiple earthing (PME)
  5.2 - Earthing Systems 5.7 - Earthed concentric wiring
  5.3 - Earth fault loop impedance 5.8 - Other protection methods
5.4 - Protective conductors 5.9 - Residual current devices (RCDs)
5.5 - Earth electrodes

5.10 - Combined functional and protective

5.4.2 - Protective conductor types

The circuit protective conductor (increasingly called the 'c.p.c.') is a system of conductors joining together all exposed conductive parts and connecting them to the main earthing terminal. Strictly speaking, the term includes the earthing conductor as well as the equipotential bonding conductors.

The circuit protective conductor can take many forms, such as:

1. - a separate conductor which must be green/yellow insulated if equal to or less than 10 mm2 cross-sectional area.

2. - a conductor included in a sheathed cable with other conductors

3. - the metal sheath and/or armouring of a cable

4. - conducting cable enclosures such as conduit or trunking

5. - exposed conductive parts, such as the conducting cases of equipment

This list is by no means exhaustive and there may be many other items forming parts of the circuit protective conductor as indicated in {Fig 5.10}. Note that gas or oil pipes must not be used for the purpose, because of the possible future change to plastic (non-conducting) pipes.

Fig 5.10 Some types of circuit protective conductor

Fig 5.11 Protective connection for socket outlet in conduit system

It is, of course, very important that the protective conductor remains effective throughout the life of the installation. Thus, great care is needed to ensure that steel conduit used for the purpose is tightly jointed and unlikely to corrode. The difficulty of ensuring this point is leading to the increasing use of a c.p.c. run inside the conduit with the phase conductors. Such a c.p.c. will, of course, always be necessary where plastic conduits are used. Where an accessory is connected to a system (for example, by means of a socket outlet) which uses conduit as its c.p.c., the appliance (or socket outlet) earthing terminal must be connected by a separate conductor to the earth terminal of the conduit box (see {Fig 5.11}). This connection will ensure that the accessory remains properly earthed even if the screws holding it into the box become loose, damaged or corroded.

Fig 5.12 Separate additional protective conductor with flexible conduit

A separate protective conductor will be needed where flexible conduit is used, since this type of conduit cannot be relied upon to maintain a low resistance conducting path (see {Fig 5.12}).


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Extracted from The Electricians Guide Fifth Edition
by John Whitfield

Published by EPA Press Click Here to order your Copy.

Click here for list of abbreviations