IT is well known to electricians that animals are much more sensitive to electric shock than human beings. Quite low voltages, of the order of 20 volts, are dangerous to cattle and horses. About twenty years ago, when rural electrification began to increase on the Continent, fatalities to these animals began to occur, and it was found necessary to devise methods for mitigating the danger. As the electrification of farms has now been begun in Great Britain, the paper by T. C. Gilbert in the Electrician for April 29, in which he discusses some of the effective safety devices used abroad, should prove useful. Wiring systems where the ‘live’ wires are surrounded by metal which is connected to ‘earth’ are perhaps the safest, at least in towns, where the mains of the water supply system, into which any leakage currents usually flow, form an excellent earth. In rural districts, earths are made by burying metal plates or pipes. In this case the resistance of the earth may be of the order of 50 ohms, and so even if a leakage current be less than an ampere, the difference of potential of the ground near where the pipe is inserted and four feet away may cause a dangerous shock to a large animal standing with a foreleg near the pipe and a hindleg four feet from it. Mr. Gilbert records a very exceptional case where no less than six cows in one farm were killed from this cause. So far as we know, no fatalities to human beings have ever occurred in this way. We have heard of cases where mild shocks have been felt in the street, when a pedestrian steps from one part of the pavement to the other, due to a fault in an underground main. The effective methods used abroad show that the risks to cattle can be made almost negligible.
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Animals and Electric Shocks. Nature 129, 754 (1932). https://doi.org/10.1038/129754a0