February 2, 2016

New Zealand farming. Electric power fencing – Glossary of terms.

Dr Clive Dalton

Amp: Unit of current.  Watts divided by voltage.

Current: It is current and the duration and rat of its low which causes a shock.  Increasing voltage increases current.  Current decreases as resistance increases.

Capacitance: Ability to store a charge of electricity.

Capacitor:  Stores electrical chares and ule as energy which builds up in the capacitor and is released by the SCR switch into the fence at approximately one per second.

Electrolysis:  Corrosion which occurs when different metals are connected in a wet environment such as with electrical connections on a fence line.

Impedance: Combination of resistance, induction, frequency and capacitance (sometimes called AC resistance).

Induction: Power transfer without contact.  For example – charging of dead or neutral fence wires which run parallel to live ones.

Insulator: A material across which current will not flow.

Joule:  Unit of energy. Watts x seconds.  Measures the ‘kick’ of a fence pulse.

Leakage: Loss of power conducted from the fence to the ground, caused by poor insulators, shorts and herbage growth on the wires.

Measurement: 500 ohms (2mS) which is the maximum a human or animal can conduct in the worst conditions e.g. with feet and hands in salt water.  5000 ohms (0.2mS) is the equivalent of a cow touching an electric wire.  ( See Siemens).

Ohm:  Unit of resistance.  The ohm scale is a reverse one – so low numbers indicate heavy load and high numbers indicate a light load.

Outrigger: Electrified wire attached to conventional fence, supported in a way to keep stock from contacting the fence.

Outrigger carrying hot wire on boundary fence

Power consumption: Electricity consumption does not increase with leakageon the fence because most energisers operate on maximum all the time and the VDR’s absorb the unused surplus.

SCR:  Silicon Controlled Rectifier which is a transistorised pulse switch.

Siemens:  Unit of conductance, leakage or load.  Reciprocal of ohm.  1 Siemens = 1 ohm, 1 millisiemens (mS) + 1000 ohms.

VDR:  Voltage dependent resistor. Prevents voltage of more than 5000 volts from leaving the power unit by short circuiting the excess voltage.

Volt:  Unit of electrical pressure which causes current to flow. Voltage = current x resistance.

Watt:  Unit of power – both electrical and mechanical.  746 watts = 1 Horse power.

Acknowledgement of information source:  To Gallagher New Zealand.

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