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Effective earthing of an Electric Fence is a perennial topic and needs to be well understood as many people still think you can skimp when it comes to adequate earth grounding. What we must all learn is the electricity must complete a full circle back to the energiser through the ground. Poor earthing will result in the reduced transfer of electrons from the ground back to the energiser invariably felt as a weak tingle or weak shocks.
Rule of Thumb;- There isn't one.
Most electric fence energisers will come with directions that state what earth rod is needed for that particular energiser. Some are simple. It can be as easy as running a ground wire to an existing fence post. Others may have a formula such as one meter of earth rod for every joule created by the energiser. It also varies with the amount of fencing attached to that energiser – a single 50 meter net on a 5 Joule energiser does not need 5 meters of earth rod. Wet soil also vastly improves the connection so reduces the requirement. The only answer is trial and error.
The ground constitutes 50% of the electrical circuit but 90% of all problems originate at poor earthing, either at the earth stake itself or on the fence. Fortunately this is easy to rectify. Additional earth stakes may be added by driving them into the ground 1 - 2 meters away from the existing stake and joining them together.
The Material that Makes a Good Earth Stake.
Copper, Aluminium, Stainless Steel, Copper clad steel or Galvanized steel rods are best in that order. Mild Steel is a poor long term option as it will react with the ground chemicals and rust. The Iron Oxide (Rust) that forms as a skin around the earth stake is a poor conductor of electricity so reducing the effectiveness of your earthing system creating a poor conducting barrier between the metal and the ground. Mild Steel rods should only be used as a temporary measure.
( Please read - Rust and it's effect on an Earth Rod.)
Location or Siting of an Earth System.
The transfer of an electrical current from the soil to the earth stack is directly dependent on the moisture content of the soil. All rods should be located in permanently moist soil, under the building eaves, in a river bed, below a dripping tap or in an irrigated flower bed. In particularly dry weather the soil around the stakes may be watered. Under a large tree is often a poor selection as these trees tend to suck up the surface moisture rapidly leaving it dry and imperfect.
A legal stipulation requires that an electric fencing earth post to be more than 3 meters away from a household earth system.
Poor electron transfer from the fence back to the earth stake is less easy to rectify. If the fence extends over 500 meters in a straight line away from the main earth post it will be necessary to add an additional earth line to the bottom of the fence and bury a stake at those intervals. Wire is a better conductor than ground so a ground rod approximately every 500 meters will greatly increase the effectiveness of the fence. This connecting wire does not need to be insulated from the ground BUT must be insulated and separate from the live wires of the fence
A Earth Return Fence
In dry climates or where the soil is very sandy resulting in poor conductivity through the soil, it will be necessary to consider an Earth Return fence. This is where the fence is constructed from equal numbers of live and earth wires to remove the ground from the electrical circuit. The animal is required to touch both wires to achieve the desired effect. An earth post is still utilised to cater for current flow through the ground.
It is generally recommended that you avoid using mild steel for grounding an electric fence, as it corrodes too readily when placed in soil. Ground rods, wires, and clamps can be made of galvanized steel, copper clad-steel, or copper. Both temperature changes and power surges will cause minor contractions and physical changes in metals. However, different metal will react differently. Therefore, when various metals are used in the same system the different properties they exhibit during these changes can promote increased corrosion and reduce the fence’s effectiveness.
Bentonite/Salt Earth System.
A bentonite/salt earth system is recommended for extremely dry soil conditions. A mixture of bentonite and salt surrounds each earth rod. The salt attracts moisture and acts as a conductor while the bentonite retains moisture over long periods of time. Stainless steel earth rods are essential to combat salt corrosion of the earth stake. A wide hole is dug and filled with the mixture with the earth stake being inserted into this.
Maintenance of your Earth System.
Finally, a little ground maintenance is required. Annually, take a wire brush to your ground rods, clamps, and wires where the three connect together. This will remove corrosion and rust. This should help to increase the power of your fence. Additionally, you should check your fences power from time to time with a meter.
Testing the Earth System;-
- Place a metal stake against the fence so it is shorting out the fence to ground,
- Use your tester between the ground and your earth-stake.
- There will always be some voltage registered but if it is more than 500 volts then you need to look at your system.
- If you have no tester then place one hand on the ground and touch the earth-stake with the other. A mild tingle is OK but if you definitely feel it then there is an issue.
These measures will all contribute to maximising the potential of an electric fence and by improving its effectiveness, allow it to achieve its desired goals.