Power Failure, Interference and Lightning Protection for Electric Fences

Part of the lightning diverter kit

Power Failure

If there is a power failure or the electric shock fails for another reason, the stock trained to electric fences still respect the fence for some time.
This time period varies quite a lot and depends on how anxious the stock are to get through the fence. It also depends on the number of wires in the fence.
In many cases it has been just two or three days before trained cattle have attempted to get through. Cattle normally graze right up to an electric fence and so it is reasonable to assume they accidentally touch the wires occasionally. This is how they find out the power is off.
If you are faced with a power failure such that your fence is inactive for more than two or three days, a battery powered energiser could get you through the emergency.

Radio, Television and Telephone Interference

Electric fences sometimes cause interference to radio, television, Internet access, or telephones. It is desirable therefore to install the energiser as far away from these items as practicable.

Some energisers have RH (radio frequency interference) suppression circuitry to overcome this problem.

Try not to install fences or connecting wires parallel to any of the following:

• normal electric power supply lines to the property
• telephone lines (underground or overland)
• radio aerial or television antenna wires.

Faults on the fence can also cause interference. Poor earthing, poor electrical connections and arcing (sparks jumping) on the fence wires are the usual causes. If interference persists, even though there are no faults and the fences are not parallel to electrical installations, the following method may prevent or reduce it:

• use a double insulated cable buried in the ground for the high voltage wire from the building housing the energiser to the fence line
• if the distance is more than 200 m, you can overland the wire in the normal way.

If your fence must run parallel to a telephone wire for one kilometre or more, divide the fence in the middle and feed power from either end to stop in the middle.

Lightning Protection

If lightning strikes the energiser or the wires connected to the energiser, the sudden surge of power to the energiser can damage it. Since the energiser could even explode or cause a fire you should house it well away from flammable materials.

Some energisers have built-in protection and some suppliers provide in-line protectors you can fit yourself. For example, Gallagher has produced an adjustable lightning diverter for added protection.
However, not all diverters give full protection. It is good practice to unplug the energiser and disconnect the fence wires during electrical storms.
A practice gaining wider acceptance is to make the earth wire the top strand of the fence. This gives a 45° umbrella-like protection in the event of a lightning strike.