Security & Electrical

An electric fence is a barrier that uses painful or even lethal high-voltage electric shocks to deter animals or people from crossing a boundary. more...

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History

The concept of the electric fence was first described in Mark Twain's A Connecticut Yankee in King Arthur's Court, in 1889, as a defensive weapon.

Electric fences were used to control stock in the United States in the early 1930's, and developed further in both the United States and New Zealand.

An early application of the electric fence was developed in 1936–1937 by New Zealand inventor William "Bill" Gallagher Snr. Built from a car's ignition coil and a meccano set, Gallagher used the device to keep his horse from scratching itself against his car. Gallagher later started a company to improve and market his invention. Today the Gallagher Group of companies is still heavily involved in electric fencing for livestock control.

Electric fences have improved significantly since the early days. Improvements include:

Polyethylene insulators replacing porcelain beginning in the 1960s. Polyethylene is much cheaper than porcelain and is not as breakable.; Improvements in electrical design of the charger (or fencer); Changes in laws. In some jurisdictions, mains fencers were unlawful until the 1950s or 1960s. In other areas, signage requirements and other restrictions limited usability.; Introduction of High Tensile (HT) fence in the 1970s in New Zealand and in the 1980s in the United States;

Design and function

Electric fences are designed to create an electrical network when touched by a person or animal. A component called a power energizer converts power into a brief high-voltage pulse. One terminal of the power energizer releases the electrical pulse along a connected bare wire about once per second. Another terminal is connected to a metal rod implanted in the earth, called a ground rod. A person or animal touching the wire and the earth simultaneously will complete an electrical circuit and will conduct the pulse, causing a painful electric shock.The effects of the electrical shock depend upon the voltage and electrical current used, and can range from barely noticeable to painful to lethal.

Early mains-driven (AC) fence chargers used a transformer and a mechanically-driven switch to generate the electrical pulses. The pulses were wide and the voltage unpredictable, with no-load peaks in excess of 10,000 volts and a rapid drop in voltage as the fence leakage increased. The switch mechanism was prone to failure. Later systems replaced the switch with a solid-state circuit, with an improvement in longevity but no change in pulse width or voltage control.

"Weed burner" fence chargers were popular for a time and featured a longer-duration output pulse that would destroy weeds touching the fence. These were responsible for many grass fires when used during dry weather. Though still available, they have declined in popularity.

Read more at Wikipedia.org