Voltage-operated earth-leakage protection

Abstract

In this paper the author advances the view that leakage protection problems must be considered upon a more practical basis, necessitating some departure from the present practice of almost purely academic treatment of the subject. Piecemeal considerations of separate sections of the whole earthing problem, earth electrodes, fuses, earth-continuity conductors, testing, etc., result in obscuration of the question, as efficient leakage protection entails the perfect functioning of each and every section of the protective system, at the same time and without reasonable chance of failure. The view is also expressed that in the search for immunity from shock, the equally important matter of protection against fire risk has been overlooked.The point has been reached where the increasing expense and decreasing security of earthing has led to some consideration of alternatives, notably multiple neutral earthing, with the connection of the consumer's casings to the neutral line, and the use of earth-leakage circuit-breakers. The rural area now represents the field of greatest difficulty combined with greatest urgency in the matter of protective questions, but the author discusses protective problems as a whole. The view is advanced that the only logical way to limit leakage voltages is by means of devices responsive to predetermined voltage limits, such as are now employed in the largest rural areas in Europe.The problems are examined in as simple a manner as possible, without recourse to complicated mathematical formulae or very involved calculations, for two reasons : first, because the divergence between theory and practice is more marked in earthing problems than in any other aspect of engineering practice, and the problems are not therefore amenable to calculation or paper consideration, and second, because these problems are normally encountered by mains and installation engineers in the course of their normal duties, and if the industry is to benefit from the practical experiences of these men over the past 20 years then any discussion of the questions involved must be placed upon the most practical basis possible.