Earth leakage protection schemes and relays

In view of the fact that faults to earth represent the most frequent type of failure to which electrical apparatus is subject, an earth leakage protective system fulfils a most important function and localises the trouble by rapid isolation of the faulty apparatus. The core balance and residual current systems of earth leakage protection were discussed in a paper entitled “Neutral Earthing and Earth Leakage Protection” in this Journal for March, 1940, and the object of the present paper is to consider various specialised forms of protection for particular types of apparatus.