7.6.3 - Electric fence controllers

Electric fences are in wide use to prevent animals from straying. In most cases they are fed with very short duration pulses of a voltage up to 5 kV - however, the energy involved is too small to cause dangerous shock. Usually animals very quickly learn that it can be painful to touch a fence, and give it a wide berth. {Fig 7.7} indicates a typical arrangement for an electric fence, the numbers in brackets in the following text relating to the circled numbers on the diagram.

Controllers may be mains fed or battery operated. Controllers must be to BS EN 61011-1, and not more than one controller may be connected to a fence (1). So that it will give a short, sharp shock to animals, the high voltage output of the controller is connected between the fence and an earth electrode. It is of obvious importance that the high voltage pulses are not transmitted to the earthed system of a normal electrical installation because the earth zones overlap (4). A method of checking the earth zone of an electrode is described in {8.6.1}. For similar reasons it is important that the fence should never make contact with other wiring systems (2), telephone circuits, radio aerials, etc; the installer must also take account of induction from overhead lines, which may occur when the fence runs for a significant distance below such a line.

Fig 7.7 - Electric fence controller

A mains operated fence controller must be installed so that interference by unauthorised persons and mechanical damage is unlikely. It must not be fixed to a pole carrying mains or telecommunication circuits, except that where it is fed by an overhead line consisting of insulated conductors, it may be fixed to the pole carrying the supply (3).