TNH Wildlife Management Solutions

EARTHING

Earthing is the most important component of an electric fencing system. In practice, most problems which occur with electric fences are caused by poor earthing.

For an electric fence to be effective the circuit must be completed. When an animal touches the fence wire the circuit is completed (closed) through to the ground, or to the earth return wires, and the current flows back, via the earth pegs, to the earth terminal of the energizer. This current flow must be good in order to deliver a decent shock to the animal. Therefore, it is imperative that the energiser is well and truly earthed. Soil that is very dry, sandy or pumice will not conduct the electric current as effectively as clay or slightly damp soil. In these less than ideal conditions, it is more difficult to get an adequate earth system to ensure the animal receives the maximum shock. It is best to choose a damp area for earth installation where possible.

The 4.3.2.1 earthing rule:

This general rule suggests you use a minimum of FOUR galvanised stakes placed THREE meters apart from each other, each TWO metres long (underground) and connected by ONE continuous wire.

It is also important to place the earthing system as close as possible to the energizer and at least 10 meters from any power supply, earth stake, underground telephone or power cable. Never connect two or more energizers to the same earth peg. Don’t use copper earth stakes with galvanised wire as this will cause electrolysis at the joins. The earth system should not be allowed to touch any building. Never connect the energizer earth to the water supply. For best results a location with permanently moist ground, such as near a stream, dam, trough, or septic absorption trenches or water tank overflow.

Purpose manufactured earth stakes are the easiest to use and consist of either galvanized steel rods or angle iron. The stakes are connected to each other and to the earth terminal of the energiser, using galvanized nuts and bolts. Alternatively, a length of galvanized water pipe can be used, but it is harder to drive in and is difficult to connect to the earth wire satisfactorily.

INTERMEDIATE EARTHING

On long fence runs, and in dry areas, there may be insufficient moisture within the soil to provide adequate current flow through the earth return system. In these situations, a fence return system is used. Earth connections are then made at regular intervals along the length of the fence. This is achieved by simply connecting the earth wires to additional earth stakes, periodically spaced. Connections should be made using line clamps and insulated cable or steel wire. Where possible intermediate earths should also be established in moist ground (eg, near a dam or stream).

TESTING THE FENCE EARTH RETURN

A poor or inefficient earth system will restrict the flow of electrons or current around the circuit. To test the earth, drive a galvanised earth state at least a meter into the ground and at least a meter away from the nearest earth stake of the fence system Then using a Digital Volt Meter measure the voltage between this installed earth peg and the nearest earth peg attached to the energiser earth system. Bring the fence line voltage down to 2K v or less by placing several steel stakes between the live wire of the fence and the ground, at least 100M away from the earth system. On a clean well-insulated fence there is very little current flow so in order to test the earth it is necessary to create current flow creating a short or leakage path. Ideally there should be no reading on the volt meter. A reading of up to 200 volts, provided the fence is shorted to below 2000volts, is acceptable. If the voltage is higher than 200 volts then the earth return wire must be checked for loose connections and / or more earth stakes must be installed along the fence line. These additional stakes must be coupled to the earth return wire.

DO’S & DON’T’S OF EARTHING

DO

Use at least 4 galvanised earth stakes each at least 1.5M long.

Drive the earth stakes into the ground at least 3M apart.

Connect the earth stakes together using a single length of insulated undergate cable or fencing wire.

Clamp the cable securely to the earth stakes

Install the earth stakes:

In moist or damp soil.

Close to the building or along the fence line for protection

At least l0M away from any mains power supply, earth stakes, underground telephone cables, power cable or water pipe.

DON'T

Connect two or more energizers to the same earth peg.

Allow any part of the earth system to touch a building i.e. bare wires.

Connect the energizer earth to mains electricity or telephone earths.

Connect the earth system to water mains.

Remember, surveys have shown that over 80% of electric fencing systems suffer from inadequate earthing. So, spend a little extra time on this important aspect of your electric fence and enjoy many years of trouble free fencing.