Electric fencing

According to (1), electric fences were used for stock control in the United States no later than 1936, and developed further in New Zealand throughout the 1950's and 1960's where improved technology and a change in laws allowed fences to be powered by mains electricity.

All electric fences are based on the idea of using regular, very short, high-voltage pulses of electricity, generated by storing energy in some kind of capacitor and releasing it very quickly. One wire is usually connected to the fence, the other to an "earth pole". An animal (which are mostly water and thus quite conductive) touching the wire and the earth simultaneously will complete an electrical circuit and will conduct the pulse, causing a painful electric shock. Animals quickly learn to avoid the painful, but harmless barrier (as do most humans :) ).

Permanent electric fencing may be constructed using conventional fencing techniques, with plain steel wire serving as the conducting wire. The wire must be kept insulated from the earth. Typical methods for doing so involve the mounting of the fence wire on plastic or porcelain insulators; other techniques include using fence posts that are themselves insulators.

Permanent electric fencing is popular in many agricultural areas, as construction of electric fences (using plain wire and lighter construction, as the fence does not need to physically restrain animals) is much cheaper and faster than conventional fences. Its disadvantages include the potential for the entire fence to be disabled due to a break in the conducting wire, power failure, or forced disconnection due to the risk of fires starting by dry grass touching the electrified wire. In practice, once animals have learned of the unpleasant consequences of touching the fence they tend to avoid it for considerable periods even when inactive.

Substandard conventional fencing can also be repaired quickly and cheaply by the addition of a single electric wire mounted as a "stand-off" using spring-loaded insulated wire mounts from the original fence.

Electric fencing is probably more popular, however, for the construction of temporary fencing, particularly to support the practice of strip grazing[?]. Typically, a single strand of wire, or flexible plastic tape embedded with conducting wire, is mounted on espeically-designed posts designed to be pressed in by the fencer's feet. Within a few minutes a large area can be fenced off. Portable, battery-powered fence "energiser" units are made for this purpose.

Electric fences were infamously used to guard the concentration camps of Nazi Germany during World War II, but are no longer used for security fencing.

References:

1. [1] (http://www.gallagher.co.nz/dynamic/profile)