Guide to Good Electric Fence Grounding
Posted by Cyclops Electric Fence on
When the energiser earth system can't absorb the increased flow of electrons from leakage, electrons find other ways of getting back to the power supply earth system. Energisers put out thousands of volts, and just one volt through the cow's mouth or teats can upset her. Here are methods to follow to avoid that:
- The energiser earth system must be installed well away -- at least 10 m (33 feet) from mains power earth peg, preferably on the opposite side of the building.
- Use 25-mm (1-inch) or larger diameter new or near new galvanised pipe driven as deeply as possible into a moist soil, each at least 10 m (33 feet) apart. Thin, black or rusty fence posts or similar are not suitable. Rust is a bad conductor. A large surface area is needed to give a large contact area between the soil and pipe.
- One metre (3 feet) of earth pipe per joule of output of the energiser is usually sufficient for satisfactory earthing in conductive soils. Long earth pipes which are driven deep into the soil give far better earthing than the same total length at shallower depths because soils are more moist and have more conductive minerals at lower levels. Two 3- metre-long pipes are better than three 2-metre-long pipes when driven deeply this way. Large diameter pipes have a greater soil contact surface, so are better than thin rods.
- Install the earth system well way from water pipes and bores which are being used. But an unused steel pipe bore can be an excellent earth if it's not rusted or broken.
- Connect the terminal marked Earth or Ground to the earth pipes by one continuous length of double insulated electric fence leadout cable -- not household or industrial cables which are made for only 400 volts, not for 10,000 volts. The cable should contain 2.5-mm (16-gauge) galvanised wire -- not thinner and not copper wire, which causes electrolysis at the joins. Bare and clamp the cable securely to each pipe with galvanised clamps. Ordinary galvanized wire can rust where it is damaged or touches the ground. Using cable eliminates this.
- It is best to have no voltage on the earth system, but a maximum of 200 volts (and up to 300 volts on a large energizer) are acceptable when the fence has been shorted out to as low a voltage as possible.
- Soils are not good conductors, so electrons spread out inclining towards moist and mineral soils when travelling back to the energizer. Aim for a moist area, work out a system of keeping the area around the earth pipes moist. If necessary, take a galvanised wire along the bottom of a fence to a moist area, and then install more earth stakes at that point. If the distance exceeds 100 metres, use two wires. Better still, use aluminium or aluminium-coated wire which is up to three times more conductive than the same thickness galvanised wire.
- Some soils are very bad conductors. If you have dry peat, pumice, volcanic ash soils, etc., or soils that are dry at any time of the year, and there is no wet area within a few hundred metres which could be used, a bentonite earthing system can be bought and used. They are a good value. The bentonite mix is made into a slurry and poured down 75-mm (3-inch) diameter or larger holes with pipes set in the centre. Keep them moist. This system can improve earthing by up to ten times.
- In extremely dry areas and on snow, use an earth wire return system. This is where there is an equal number of live and earth wires kept well apart on the fence. The earth wires are joined with joint clamps (like the live wires) and connected to the energized earth terminal. The earth wires should also be earthed adequately (no voltage on them) every kilometre. These also act as lightning conductors, keeping it away from energizers.