Protection against shock to earth

Two outstanding events have had a profound effect on UK earth-leakage practice: the introduction of highly sensitive residual-current earth-leakage devices at the beginning of the 1960s, and the prohibition of the use of water-supply pipework as the sole earthing electrodes of installations in the 14th edition of the IEE Wiring Regulations, 1966. The advent of 20¿¿30 mA protection aroused considerable scepticism because of fears that it would be subject to nuisance tripping; in practice, this has only rarely been experienced, but unfortunately mistakes have occurred in the application of both high and medium-sensitivity residual-current earth-leakage devices. This paper, based principally on practical experience, has been written with the object of increasing the interest in and greater general understanding of this vitally important subject, and is mainly confined to applications for standard 415 and 240 V supplies.