This article relates to energisers installed at agricultural premises to restrict the movement of livestock. It does not cover electric fences intended for security purposes. A typical example of such an electric fence arrangement is shown in Fig 1.
Method of protection against electric shock
The output of an electric fence energiser that complies with the requirements of BS EN 60335-2-76provides protection against electric shock, by means of limiting the current which can pass through the body of a person or livestock to a value lower than that likely to cause danger.
Importance of correct installation
An electric fence installation is designed to stimulate a response following contact. The person or animal in contact with the fence and Earth receives the unpleasant sensation of electric shock.
Table 1 gives the limits on the output characteristics of electric fence energisers, as given in BS EN 60335-2-76.
Output characteristic Value Maximum impulse repetition rate 1 Hz
Maximum duration of impulse 10 ms
Maximum discharged energy per impulse 5.0 Joules
The output limits of an energiser should not normally cause an electric shock as defined in BS 7671as: ‘a dangerous physiological effect resulting from the passing of an electric current through a human body or livestock’.
However, there can be danger of electric shock (as defined) if the person or animal becomes entangled with the fence and – being unable to break contact, receives a succession of impulses. To avoid such danger it is important that an electric fence is correctly installed in accordance with the recommendations referred to in this article. Correct installation also reduces the possibility of a dangerous voltage from another system, such as an induced voltage from an overhead power line, appearing on an electric fence.
Barbed wire or razor wire should not be electrified by an energiser or used in the construction of an electric fence. However, a non-electrified fence incorporating a barbed wire or razor wire may be used to support one or more offset electrified wires of an electric fence intended to restrict the movement of animals. The supporting devices for the electrified wires should be constructed so that those wires are at least 150 mm from the vertical plane of the non-electrified wires, as shown in Fig 2. The barbed wire or razor wire should be earthed at regular intervals, following the energiser manufacturer’s recommendations. (Section BB.1 in Annex BB of BS EN 60335-2-76.)
Note. The minimum separation distance of 150 mm between the electrified wires and the vertical plane of the non-electrified wires should be maintained for the complete length of the fence used to support the electrified wires.
Not more than one energiser
Not more than one energiser or one independent fence circuit of the same energiser should be connected to one fence (Section BB.1 in Annex BB of BS EN 60335-2-76 refers), otherwise, the combined discharge of energy may be too high for shock protection to be achieved.
RCD (residual current device) protection
There are available a range of energisers that can be operated using mains, solar, or battery (6 V, 9 V or 12 V) or operated from a dual main or battery supply. Where the energiser is to have a mains supply, it is advisable for the circuit to be provided with additional protection by an RCD. The RCD should meet the requirements referred to in Regulation 415.1.1. That is, it should have a rated residual operating current, IΔn, not exceeding 30 mA and an operating time not exceeding 40 ms at a residual current of 5IΔn, and comply with the appropriate British Standard.
An electric fence energiser and the wiring system and other electrical equipment used to supply it should have, or be provided with, additional protection to give at least a degree of ingress protection of IP44. Where necessary, a higher degree of protection as appropriate to the external influences should be provided (Regulations 512.2.1 and 705.512.2 refer). Unless situated in a benign environment, such as an office or domestic enclosure, the wiring system and other equipment supplying the energiser should also be suitably selected and erected to withstand the conditions of water, high humidity and dusts to which it may be exposed, as well as vermin and corrosive substances such as animal waste.
In order to meet the above requirements, and give the appropriate degree of ingress protection, a socket-outlet and plug used to supply an electric fence energiser may need to be of the industrial type conforming to BS EN 60309-1, or BS EN 60309-2 where interchangeability is required (Regulation 705.553.1 refers). Alternatively, a socket-outlet that accepts a general-purpose plug (such as a BS 1363 plug) and is specifically designed for use outdoors or in areas exposed to dust and/or splashing water may be suitable to supply the energiser, provided the appropriate degree of ingress protection is provided when the plug is in the socket-outlet.