The IEE Wiring Regulations Explained and Illustrated, 2nd Edition

The IEE Wiring Regulations

domestic bell installation, where the transformer is to BS 3535.

Note that bell wire is usually only suitable for 50-60

V,

which

means that it should not be run together with circuit cables of

higher voltages.

Reduced voltage systems

[IEE Regs 471-15]

The Health and Safety Executive accepts that a voltage of

65 V

to

earth, three phase, or

55 V

to earth, single phase, will give protec-

tion against severe electric shock. They therefore recommend that

portable tools used on construction sites etc. be fed from a

110 V

centre-tapped transformer to BS

4343.

Figure 16 shows how

55

V

is derived. Earth fault loop impedanc