The use of protective multiple earthing and earth-leakage circuit-breakers in rural areas

This paper describes investigations made to ascertain to what extent consumers in rural areas are protected from risk of shock with methods of earthing at present in use, and what changes in practice might be desirable, with special reference to protective multiple earthing. The investigation shows that present safeguards are inadequate. Recommendations are made which it is believed will lead to material improvement, but further experience and experiment will be necessary before the matter can be put on an entirely satisfactory footing. It has been realized for some time that in rural areas fed by overhead lines where no water mains exist the protection afforded by ?ordinary earthing? is not entirely satisfactory. With this in mind an investigation was undertaken by the E.R.A. with a view to finding means for improving the situation. Alternative methods of protection are provided by earthleakage circuit breakers, or the use of the neutral to carry the fault current. This latter method, known throughout this paper as ?protective multiple earthing,? is subject to the disadvantage that the frameworks of apparatus connected to the neutral rise to the same voltage above earth as the neutral conductor. It was found from field tests, however, that the voltagerise of the neutral did not exceed a value dangerous to human beings under normal operation, and that even animals would be protected if the statutory voltage-drop were not exceeded. No interference with the satisfactory working of the telephone system was observed during any of the tests. Other possible sources of trouble due to the use of the protective multiple earthing system have been considered in some detail. An investigation has also been made to find the tripping voltage of earth-leakage circuit breakers which have been in use for a period of about 2 years. The tests were made by Mr. E. Fawssett in the electricity supply area of the Dumfriesshire County Council. The paper concludes with the major deductions re- ached from the practical tests, some conclusions respecting protective multiple earthing in general, and, finally, recommendations respecting existing and new installations and certain proposed conditions which should be complied with before protective multiple earthing is permitted. The Director of the E.R.A. will welcome comments from any who may have occasion to make use of this paper.