How it works
Electricity flows only when it can complete a circuit, for example from the source of power along a conductor, such as a wire, and back to the source again. The electricity flows as a result of electrical pressure, which is measured in volts. Fence controllers are designed to work on a 220-240V mains supply. Where mains is not available, a 9V or 12V battery energiser can be used. The current is passed through the fence in pulses, to allow the person or animal touching the wire to release their hold in the interval between pulses.
Many different models of energisers are available, which vary according to their maximum discharged energy per pulse, and their ability to maintain current flow under lush vegetation conditions. In choosing an energiser, take into account the type of animal to be controlled, the length of fence, the type of vegetation, the wire type and number of wires. Manufacturers’ literature gives detailed advice on selection of suitable energisers and fencing systems. Energisers can be powered by mains electricity, battery, solar or wind power.
The diagram above shows the pathway of the current. The value of the current passing through the animal depends on the voltage along the line, determined by the output of the energiser, and the type of ground which forms the earth return pathway. Wet ground is a good conductor, and current flow is increased. Dry, stony or rocky ground has a higher value of resistance to current flow. A soft-footed animal such as a dog has less resistance than an animal with hooves. A person in wellington boots will feel less shock than a person in canvas shoes.
A voltmeter, available from fencing suppliers, can be used to show the electrical condition of the fence, to pinpoint faults, and to check the efficiency of the earthing system.
Installation and earth
The manufacturer’s instructions will include detailed advice on the installation of a mains energiser, which should be mounted near the mains supply. The output earth terminal of the energiser must be connected to a separate earth point, and not to the earth of the mains supply. The energiser earth must be at least 10m from the energiser or from any other metal, such as a shed roof, water pipe or mains earth.
The earth should be installed in the wettest possible place, such as a stream bed or permanently waterlogged ground. The earth is made with special galvanised earth stakes, which are set nearly to their full depth into the ground, and joined with clamps to the earth wire. Alternatively, an earth can be made by burying two or three new sheets of galvanised corrugated iron, a water tank or similar in moist ground, connected to the earth wire with a heavily galvanised clamp, sealed against corrosion. For full details see manufacturers’ instructions. Installation should only be done by a competent electrician.
Other safety requirements
- More than one energiser should never be used on the same fence line.
- Fence lines on separate energisers should at no point be nearer than 2m to each other.
- Fit warning signs, available from electric fencing suppliers, on all fences to which the public have access.
- Stiles and gateways on public paths must be insulated or non-electrified.
- Electric fence lines should not be attached to electricity supply poles.
- If electric fences have to pass beneath power lines, they should do so at right angles. Fence lines should never run parallel to power lines.
- High-powered battery energisers in a faulty condition can be as dangerous as a mains energiser. If ‘multi-pulsing’ occurs, when the interval between pulses becomes shorter than normal, fatal conditions can result.
- Crossing of public roads must be made with either an underground cable, or an overhead wire at least 5m above the road surface. The relevant road authority must be consulted.
- An electrified fence line should not run parallel and close to a telephone line.
