01 May 2025

Selecting the right electric fencer to suit your farm

With so many options available, it is often a challenge to select the right size electric fencer needed on-farm, Teagasc Beef Specialist, Catherine Egan shares some key considerations and some areas to troubleshot if your fencer isn’t working as it should.

On many farms, a mains fencer is used on the home block and perhaps battery or solar options are used on outblocks if there is no electricity available. When selecting a fencer, also choose one with a capacity greater than the area needed to be fenced to ensure that adequate power is supplied. There are many benefits of each fencer type, as outlined in table 1 below.

Table 1: Installation, use and key benefits with mains, battery and solar fences

What size fencer?

Fencers are mainly advertised in terms of output joules and stored joules. Don’t get these confused, and be aware of which is on the charger. A charger may advertise 30 joules, but only refer to the stored joules (a fence charger will always store more joules than it outputs). Stored joules represent the amount of power stored inside your charger. This is ran through an output transformer, which converts the power to a higher voltage. Some of the power is lost during this conversion.

Output joules refer to the actual output of the charger – the power available to shock the animal. The size of fencer depends on the area to be fenced. Always choose a fencer to match the area. It is better to choose a fencer greater than your requirement rather than less than recommended and expect it to cover more area than advertised.

Table 2: A guide to mains fencer output and area covered

Note: This is a guide. Always read and follow the manufacturer’s guidelines.

Battery fencers

Battery fencers are used for short or temporary fences where portability and flexibility are the main considerations. A dry battery is used in many cases. While a wet 12V Battery allows rechargeable batteries to be used and facilitates a more powerful battery powered fencer.

Table 3: A guide to battery fencer output and area covered

Note: This is a guide. Always read and follow manufacturer’s guidelines

How mains fencers work?

Fencer (Energiser) steps up volts to 8,000 to 11,000 volts approximately through a transformer. Each pulse lasts 0.003 of a second. The high voltage electricity is fed to the fence line wire. An earth lead is securely earthed into the ground by means of metal bar. When livestock touch the fence wire, the circuit is then completed giving a shock.

Troubleshooting

Checking the installation

Ensure the connections between fencer and fence are firm and with a good connection. If the wires are passing through a wall you need to make sure that they are properly insulated. If this is not done, there is the possibility of power being diverted from the fence into the ground. All installations must be open circuit with the outgoing wire fully insulated to avoid shorts to earth. All joints and connections should be made simply, firmly and above all be very tight, using the correct joiners for the purposes and good quality insulators. Regular inspection of the line is essential of permanent fences. Weeds and branches touching the line should be removed. Avoid vegetation growth or other items touching the wire fence as this reduces efficiency and performance, particularly during damp and wet conditions or periods of lush growth.

Earthing system

Without an earthing system for the fencer, there would be no shock at the fence line. An earthing system works in much the same way as an aerial does for a radio but instead of collecting airwaves, the earthing system picks up electrons from the ground, which are transmitted with each pulse out along the fence line. The stronger the fencer the better the earth required. Electrical current passes through soil but does so more easily in moist or mineral soils than would be the case in dry stony soil. Therefore, before deciding how many earth bars are required, take three factors into consideration:

1. The type of soil.
2. High power or low power fencer.
3. The load one can expect on the fence system and the length of fence.

Earthing/grounding rod

Use the proper type of grounding rod. In most cases, pipe or rebar can be used. The grounding rod needs to be made of galvanized steel and also needs to be at least four feet in length for best results. Using copper rods will diminish the overall effectiveness of the electrical fence system. In some cases, it may be necessary to add several grounding rods to the grounding system. In fact, the majority of electrical fence systems will actually require at least three grounding rods. These rods should be about 10 feet / 3m apart and should be placed at the start of the fence. Grounding rods can actually interfere with phone service as well as electrical lines that may be located on the farm. For this reason, it’s important to place grounding rods as far away as possible from utilities. This is especially true in relation to phone lines.

Installing the earthing system

For the exact number of earth bars to be used, refer to the manufacturer’s guide. Having decided on the number of bars required for the size of your fence, dig a trench 150mm deep from where the first bar is going to be, to where the last one is. Then using 1m galvanized rod earth bars, drive all bars, spaced 3m apart, down until they are flush with ground level. Connect heavy duty High Tensile Underground Cable from one earth bar to the other until all earth bars are connected in a daisy chain manner – not breaking the connection from the first earth bar to the last. Ensure they are securely bonded. Double insulated cable is UPVC coated 1.6mm/2.6mm mild steel wire. It is highly recommended for permanent electric fence installations to ensure all the energy from your electric fence fencer gets to your electric fence line. This versatile cable is used to also connect your fencer to your earthing system and to carry high voltage power under your gateways.

Checking earthing system

When the earthing system is installed, it is vital to test it. First you need to simulate heavy vegetation loading on the fence line. Place an iron bar in the ground about 100m out along the fence and lean it against the fence wires. Plug in the fencer and check the voltage reading along the fence line. If it reads 1,000 volts or less, a sufficiently heavy load has been put on the fencer. If the voltage is still above this, place more iron bars along the line until the voltage drops to 1,000 volts or less. Leaving this load on the line, take a voltage reading on the earthing system. A small reading on the earthing wire is ok as long as it does not exceed 300 volts. If it does exceed 300 volts, the earthing system is not sufficient, and you have to install more earth bars.

Lightning diverter system

It is recommended that all permanent fencers be fitted with a lightning diverter to help protect from lightning damage. It diverts lightning from the fence to the earth to protect the fencer.

Visibility and maintenance

Visibility of an electric fence is very important too. The animal will remember the shock it received and will respect the fence as a barrier. It is important to monitor the voltage of the fence on a weekly basis to ensure there is sufficient current throughout the fence line.

For further information, view the Teagasc Beef Farm Infrastructure Book here.