Saturday, April 18, 2009
How does an electric fence work?
The positive terminal in the energiser sends out a charge. It is normally connected to the electric fence tape.
For a shock to be useful, it needs to cause a muscle in the animal to contract which means the shock needs to be across the entire muscle, not just part of it.
The negative terminal on the energiser is generally connected to the ground via a metal rod (called an earth stake) driven into the ground at least 900mm.
For as long as the electric fence wire and the earth don’t touch, electricity won’t flow as there is nothing joining them. But once something that is standing on the ground also touches the wire, then the circuit is complete and electricity can now flow from one terminal to the other. The animal touching the wire is the conductor between the fence and the earth.
Energisers send out pulses of electricity - generally about one every one to two seconds. The fence is not permanently live like your power sockets in the house. This enables the shock sensation to occur and then stop – allowing for the animal to step back.
For a shock to be useful, it needs to cause a muscle in the animal to contract which means the shock needs to be across the entire muscle, not just part of it.
Testing your electric fence
So you suspect your electric fence isn't working? Below is a generally accepted method for finding and then eliminating the fault.
1. Test the fence – what voltage have you got
•7,500 volts or more – full operating voltage
•6,000 Volts - good
•4,500 Volts – still ok
•3,000 volts – bit suspect
•1,500 volts or less – inadequate
2. Test the energiser
•Disconnect the fence wire from the positive terminal. Test the voltage from the positive terminal to the earth stake. Not enough volts – it’s the energiser.
3. Test the earth
•Check the voltage of the earth rod. If the earth is showing more than 300 volts, then the earth system is inadequate and needs upgrading
4. Check first point of contact
•Go to the first point of contact with the fence wire. Disconnect from the fence. Take a reading before the fence wire. Not enough volts – problem is with the insulated cable.
5. Walk the fence line
•Looking for visible signs of deterioration
•Looking for vegetation touching the wires
•Listening for pulse shorting out
6. Still struggling?
•You might try an fence fault finder
1. Test the fence – what voltage have you got
•7,500 volts or more – full operating voltage
•6,000 Volts - good
•4,500 Volts – still ok
•3,000 volts – bit suspect
•1,500 volts or less – inadequate
2. Test the energiser
•Disconnect the fence wire from the positive terminal. Test the voltage from the positive terminal to the earth stake. Not enough volts – it’s the energiser.
3. Test the earth
•Check the voltage of the earth rod. If the earth is showing more than 300 volts, then the earth system is inadequate and needs upgrading
4. Check first point of contact
•Go to the first point of contact with the fence wire. Disconnect from the fence. Take a reading before the fence wire. Not enough volts – problem is with the insulated cable.
5. Walk the fence line
•Looking for visible signs of deterioration
•Looking for vegetation touching the wires
•Listening for pulse shorting out
6. Still struggling?
•You might try an fence fault finder
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