Trial Showing the Effect of Rust on an Electric Fence Post

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electricity

Effective electric fencing is highly dependent on an effective electrical circuit that includes a section that goes from the animal through the ground to the earth stake and hence back to the energiser. This then completes the circuit and results in the shock that is the effective part of the fence – persuading the target not to mess with this fence.

Obviously there are factors that inhibit this transfer of power, poor foot contact with the ground, horse wearing a blanket amongst others but the principal item that has been looked at is the component of the earth stake. Many installers simply make use of a length of mild steel lying around, drive that into the ground and connect it to the circuit. Initially this is fine but steel is affected by chemicals in the soil and will in time form a coating of rust between it and the soil. Rust is a naturally occurring phenomenon when certain metals are exposed to oxygen and water for a length of time. The actual chemical make-up of rust is 4Fe + 3O2 = 2Fe2O3.

This rust is a poor conductor of electricity so as the rust forms so the ability to transmit electricity diminishes. This rust formation is dictated to by the availability of both water and air plus may be sped up by other factors such as warmth (a steel rod will rust faster in warm soil) and the presence of an electrical current. If you have two different metals ( the metal rod and other metals commonly present in all soil) in an electrical environment then effectively a battery is created. This environment allows for the rapid transfer of electrons hence the rapid creation of rust on the surface of the metal rod you are hoping to use for your Electric Fence.

A trial has been completed to test the effect of a mild steel rod in an electric fence. Two parameters were utilised:-

1. An energiser connected to the ground but only switched on to take a reading, effectively a test of the natural rusting of a metal bar.

2. An energiser connected to the ground and constantly on. This would be the other end of the scale with power continually flowing in the circuit.

The transfer of electricity was measured at regular intervals over 40 months and the resistance between the ground and the earth post measured. The post with the constant current lost 46% of its carrying capacity over that period whilst the control lost 17% over the same period

From this it is easy to see the effect of electricity on a plain mild steel rod being used as an electrical earth. It is important that a galvanised steel, stainless steel material or copper be used for grounding an electric fence.

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 Electric Fencing earth stakes may be added by driving them into the ground about 2m away from the existing stake and joining them together. Copper, Stainless Steel or Galvanized steel rods are best as mild steel will rust so creating a poor conducting barrier. All rods should be 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.

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Source by P. Savory