Electric fence basics
An electric current will only flow when a circuit is completed. If someone or something is only connected to one side of the circuit, electricity will not flow through him or it. An electric fence uses this principle to work. Pulses of electricity flow into the fence, electrifying it. Meanwhile, pulses of electricity with the opposite polarity flow into the ground via a ground rod--a large metal spike attached into the earth. If a person, animal or plant touches both the ground and the fence at the same time, the circuit is completed and electricity flows from the fence through the victim to the ground and back to the other terminal of the fence charger.
Pulsed fence chargers
Pulsed fence chargers send a voltage spike through the fence about once every second or two. A device called a step-up transformer takes electricity from a power source such as a 120-volt line and increases the voltage dramatically. When alternating current flows through a coil, it creates a moving magnetic field. If there is another coil of wire nearby, that magnetic field creates an electric current in the second coil. If the second coil has more turns of wire than the first, the second coil will have a higher voltage. A timer switch turns on briefly every second or so, sending a pulse through the fence and another pulse through the ground. If nothing completes the circuit, very little electricity is used. If something connects the ground with the fence during that pulse, however, it completes the circuit and receives an electric shock.
Capacitor chargers work differently. The capacitor temporarily stores a small amount of electricity. Meanwhile, a small voltage runs into the fence. If someone touches the fence, that voltage triggers an electronic switch, which discharges the capacitor into the fence. Pulsed charges can vary considerably, but the capacitor always holds the same amount of electricity. That makes capacitor chargers more reliable and safer than pulsed chargers, which can give different shocks depending on conditions.
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