The IEE Wiring Regulations Explained and Illustrated, 2nd Edition

The

IEE Wiring Regulations

Earth fault loop impedance

[IEE Regs Definitions]

As

we

have seen, circuit protection should operate in the event of a

direct fault from phase

to

earth.

The

speed

of

operation

of the

protection is of extreme importance and will depend

on

the mag-

nitude

of

the fault current, which

in

turn will depend

on the im-

pedance

of

the earth fault loop path.

Figure

10

shows this path. Starting

at the

fault,

the

path

comprises:

1 The circuit protective conductor (CPC).

2 The consumer's earthing terminal

and

earth conductor.

3 The return path, either metallic

or

earth.

4 The earthed neutral

of

the supply transformer.

5 The transforme ...