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This article is about the type of Fence . For the Form Of Sport Fencing or for other meanings, see Electric Fencing (disambiguation) . An electric fence is a barrier that uses painful or even lethal high-voltage Electric Shock s to deter animals or people from crossing a boundary. 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 1930s, and electric fencing technology developed 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 Sr. 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 the design. In 1962, another New Zealand inventor, Doug Phillips, invented the non-shortable electric fence based on capacitor discharge. This significantly increased the range an electric fence could be used from a few hundred yards to 35 miles, and reduced the cost of fencing by more than 80%. The non-shortable electric fence was patented by Phillips and by 1964 was manufactured by Plastic Products, a New Zealand firm, under the name "Waikato Electric Fence." This idea was a major contributing factor enabling New Zealand to become a world leader in efficient pastoral farming.This non-shortable design is the system that is now used on farms throughout the world today. Doug Phillips went on to develop and patent other improvements to electric fence technology, but has rarely been recognised or credited for his contribution by the industry. The Gallagher firm and other manufacturers obtained the Phillips patent in 1975, 3 years before it expired. 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:
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 alternating current (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. Modern "low impedance" fence chargers use a different design. A capacitor is charged by a solid-state circuit, upon contact with a grounded animal or person, the charge is then released using a Thyristor or similar solid-state component. Voltage is consistent due to electronic output controls, within the limits of output power. Pulse width is much narrower, often about 10 microseconds. This design works for either battery or mains power sources. Permanent electric fencing may be constructed using conventional HT 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. In the U.S., permanent electric fence is most often run using soft steel wire, above or in front of a woven wire or barbed wire fence that provides a physical barrier. However, high quality synthetic fencing materials are also beginning to be used as part of permanent fences, particularly when visibility of the fence is a concern. USES Agriculture 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, the conducting wire being hooked on the woven wire or barbed wire that may make up the rest of the fence, 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. Some other animals learn to either run under the fence quickly, thus avoiding shock, or to force other animals to destroy the fence -- Hucul Horse s are known for this trick. 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 Managed Intensive Grazing , popularly known as rotational or "strip" grazing. Typically, one or two strands of wire, or flexible synthetic tape or rope embedded with conducting wire, is mounted on specially-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- or solar-powered fence "energiser" units are made for this purpose. Ranching Electric fencing is commonplace in Ranch ing and Livestock -management settings. It is used both to keep livestock within designated boundaries and also to keep predators and other unwanted animals out. It is an attractive choice for ranchers because few materials are required compared to traditional physical barrier fences, resulting in lower cost. Additionally, the risk of damage to livestock is lower compared to Barbed Wire physical barriers. This is especially the case for Horse s. Wild animals Electric fences are useful for controlling the movements of wild animals. Examples include deterring deer from entering private property, keeping animals off airport runways, and preventing geese from soiling areas used by people. Security Non-lethal fence Non-lethal electric fences are used to prevent trespass by both private and government-sector bodies. These include housing communities, commercial factories or warehouses, prisons, military bases, and government buildings. Livestock-type electric fences are occasionally employed to discourage suicide attempts on tall structures, and to reduce the incidence of graffiti and other petty crime. Lethal fence Electric fences designed to carry potentially lethal currents can be used for anti-personnel purposes.
Other uses Recent innovations have included the use of electricity to monitor fencing for Intruder Detection as opposed to providing an electric shock to discourage entry. Buried Electric Fences , called "invisible fence," are sometimes used to contain Dog s, who wear a specialized collar when outside that gives a mild shock if the dog crosses the fence line. Humans and other animals are unaware of the buried line. Electrified fences were also used in the book and film Jurassic Park , in an attempt to contain the dinosaurs. INTERFERENCE AND UNWANTED EFFECTS Electric fences have the theoretical potential to radiate a significant amount of energy, acting like an Antenna Or Aerial . Poorly maintained electric fences (with insufficient grounding or bad design) can interfere with, and significantly degrade, the performance of nearby telephone and data connections. SEE ALSO REFERENCES EXTERNAL LINKS
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