I understand basically that the current, or amps, are what cause harm, but based on Ohm’s law, V=IR, for the amps to be so low with such high voltage, the resistance must be very high. So why do you need such a high voltage in the first place? Wouldn’t that require a transformer to step up the voltage? And doesn’t such a high voltage create a safety risk, for instance if a conductor with lower resistance came into contact with the voltage source? If you want low amps as not to electrocute animals/people, would it not be easier to use lower voltage?
Just curious and trying to understand. Electricity is like magic to me.
In: Physics
Practical explanation from a sheep rancher: the voltage must be high because the resistance *is* high. Sheep in particular are well insulated, and the return path for the current (the ground) is often dry.
Hard dry hooves on dry ground and a wool covered animal make hard conditions to deliver a shock.
Here’s the electrician part of the explanation. Fence wires are long and cheap, made of high resistance steel. When transmitting power long distances, you lose power to the resistance of the wire. This power heats up the wire. P=I squared R. Notice how voltage is not in this equation.
Now P also = VI. So to deliver the same power over a long wire without losing as much to resistance of the wire, you increase the voltage and decrease the current. So even for easier to shock animals, you want high voltage to cover the miles of fence.
The reason the fence charger is safe is because the *energy* is limited. It is delivered by capacitor discharge. The capacitor is a little energy tank that can deliver high power for a short time. It fills up the capacitor and then delivers that energy to the fence. This is what makes the ticking sound you hear from a fence charger. My fence charger has an **18 joule** capacitor. So no matter what touches the wire, it is getting a maximum of 18 joules of energy delivered to it.
Latest Answers