In wet environments or where a person is working in close contact with an expanse of earthed
metal work, the use of electricity should be avoided as far as possible such as by the use of air driven rather than electrical tools. Essential electrical services such as lighting should work at a maximum of 25V with a supply centre-tapped to earth and the light fittings should be out of reach. Double pole fusing and switches will be necessary if a centre-tapped system is adopted.
Instead of a centre-tapped system a safety extra low voltage system completely isolated from earth can be used. A disadvantage is that an earth fault on one pole of the supply can go undetected. The supply is no longer unearthed and a shock to earth is thus possible if a second fault develops to an external conducting part.