PRINCIPLES OF ELECTRIC FENCING
Advantages of electric fencing
How an electric fence works
Basic electrical terms
How performance can be measured
Measuring energiser performance
Some questions and answers

ADVANTAGES OF ELECTRIC FENCING
Effective stock control achieved by physical, visible and psychological means.
Animal friendly:
Risk of injury lower than for non electric fences especially barbed wire.
Less expensive to install than conventional fencing.
Versatile
easily and quickly erected
variety of design possibilities
can be permanent or portable
existing fences can be electrified
Can be used to improve pasture and grazing management.
Low maintenance
Note : To obtain the full advantages of electric fencing, correct installation using high quality insulators and accessories is essential.
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HOW AN ELECTRIC FENCE WORKS
An electric fence is simply one or more wires carrying a pulsing electric charge.
Any animal coming into contact with the wire receives an unpleasant but harmless electric shock.
Unlike conventional fences, an electric fence is not so much a physical barrier as a psychological or mental one.
The stock "learn" not to approach the fence.
In simple terms:
The energiser generates high voltage intermittent pulses.
Each pulse consists of a short burst of intense electrical energy released onto the fence through the lead-out wire in a controlled way over a period of about 0.3 milliseconds.
Any animal touching a live wire receives a memorable but harmless shock by completing the electric circuit back to the energiser via the ground earth system.
To work effectively an electric fence must have:
Sufficient voltage on the fence line to penetrate resistance of animal's skin.
Enough energy [power] in the energiser to electrify the actual distance of wire.
Excellent earthing and wire insulation.
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BASIC ELECTRICAL TERMS
a.c
Alternating current or mains power supply.
Your local supply will be within 220/240 volts ac.

d.c.
Direct current or battery power supply.

amps
Electrical rate of flow.
One amp is the current that results when a pressure of one volt is applied across a resistance of one ohm.
Volts/amps = ohms

ohms
Electrical resistance.
One ohm is the amount of resistance that will limit the flow rate to one amp when a pressure of one volt is applied
Volts/amps = ohms
load [loss of voltage]
Anything that draws power from the energiser puts a load on the fence line.
This can be in the form of leakage or shorts and is measured in ohms.
The lower the resistance of the load, the great is its effect.

short [short circuit]
In electric fencing this implies a large energy loss from the fence line to earth, such as an earth wire touching a live wire, long lengths of electrified wire lying on the ground etc.
A total short circuit = 0 ohms.[Example, broken post insulator]

leakage
In electric fencing this implies small energy losses from the fence line to earth such as seasonal foliage growing over the fence line, faulty insulators etc.

low impedance
In effect the internal resistance of an energiser.
All modern energisers are low impedance = maximum energy transferred to fence.

voltage
Electrical pressure.
One volt is the pressure necessary to cause one amp to flow through a resistance of one ohm.
Ohms x Amps = Volts

watts
A unit of power
A flow of one amp at a pressure of one volt = one watt.
Amps x Volts = Watts

joules
Electrical energy.
One joule is the energy required to produce one watt for one second.
Watts x Seconds = Joules. Joules per impulse are the measure of the power of an energiser
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MEASURING ENERGISER PERFORMANCE
Energiser performance really relates to the ability to deliver a sufficiently high voltage [shock] onto a fence line.
This means that different performance is required of a small portable energiser designed to power 500m [550 yds] of wire, than from a high power energiser which can handle over 200 kms [120 miles].
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HOW CAN PERFORMANCE BE MEASURED ?
Several factors are important:
measure energy in output joules at specific loads or the maximum value.
pulse shape
look at voltage under load
distance is very dependent on fence conditions and less relevant than stored energy. This can be quoted in single wire terms of known electrical resistance.

Pulse Shape
The shape of the electrical pulse produced by the energiser also influences its performance on the fence line.

Quoting distance
The performance of an energiser in distance terms can be quoted on the basis of length of a single strand wire of known electrical resistance with ideal insulation and fence construction.
Generally, a multi-wire fence will carry current further than a single wire.
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SOME QUESTIONS AND ANSWERS ON ENERGISER PERFORMANCE
Q. HOW IS A FENCE LINE ENERGISED ?
A. By successive, high voltage, short duration pulses of electrical energy at approximately one second intervals

Q. WHAT IS STORED ENERGY?
A. The energiser's electronic circuitry takes electrical energy from the power source [mains or battery] and accumulates it in the storage capacitors. This energy is the stored energy and is measured in joules.

Q. DOES STORED ENERGY INDICATE THE ENERGY AVAILABLE AT THE FENCE TERMINALS TO ELECTRIFY YOUR FENCE?
A. No. It simply indicates the energy stored in the capacitors.

Q. WHAT IS OUTPUT ENERGY ?
A. Triggered by electronic circuitry, the stored energy is discharged through an output transformer to the energiser's fence terminals.
This is the output energy and is measured in joules.
The effective output energy of this pulse is dependent on these factors:
The stored energy.
The efficiency of the output circuit.
The Fence Load connected to the terminals.

Q. WHAT SHOULD I LOOK FOR WHEN CHOOSING AN ENERGISER ?
A. The best performance characteristics in the size range to suite your needs.
This means:
The maximum output pulse energy available at the fence terminals of the energiser.
This should be stated in joules.
The highest available voltage under heavy fence load conditions ie not pure wire resistance.

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