An electric fence energizer converts mains or battery power into a high voltage pulse. The energizer releases this pulse on to an insulated fence line about once every second. The pulse itself is only around 150 microseconds long.
This pulse is commonly referred to as the “shock” and is felt by any animal which touches an electrified fence. When the animal makes contact with the fence the circuit is complete. It is at this point the animal receives a shock. The diagram below shows how the current flows from the energizer down the fenceline and through the animal. The current then flows through the earth back to the ground system and completes the circuit. It is the shock which deters the animal from putting pressure on the fence line.

An electric fence is a psychological barrier rather than a physical one so the animal must be educated to respect the fence. The pain that an animal feels is short lived and does not physically harm the animal, unlike barbed wire which can cause severe cuts and long lasting pain whilst also damaging the hide.