Design and function
Detail of an electric fence material made of synthetic cord with metal interwoven through it, attached to a steel fence post with a plastic insulator. Electric fences are designed to create an electrical circuit 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 a
n 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 or earth rod. A person or animal touching both the wire and the earth during a pulse will complete an electrical circuit and will conduct the pulse, causing an electric shock. The effects of the shock depend upon the voltage, the energy of the pulse, degree of contact between the recipient and the fence and ground and the route of the current through the body; it can range from barely noticeable to uncomfortable and painful. Fence energizers
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. 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. Fencing material
Electrified palisade fences are usually made from painted mild steel, galvanize steel, or aluminums. Typically the fences are 2.4 meters (7 ft 10 in). The palisade fence is mechanically stronger than a typical steel cable electric fence to withstand impact from wildlife, small falling trees and wildfires. Security
Non-lethal fence
Non-lethal electric fences are used by both private and government-sector bodies to prevent trespass. These include freight carriers, auto auctions, equipment rental companies, auto dealers, housing communities, commercial factories or warehouses, prisons, military bases, and government buildings. Many of these electric fences act as monitored burglar alarm systems in addition to causing an uncomfortable shock. Electrified palisade fences are used to protect isolated property and high security facilities, but also around some residential homes. Electric fences are occasionally employed to discourage suicide attempts on tall structures, and to reduce the incidence of graffiti and other petty crime. Due to the high levels of crime in South Africa, it is common for residential houses to have perimeter defenses. The City of Johannesburg promotes the use of palisade fencing over opaque, usually brick, and walls as criminals cannot hide as easily behind the fence. In the City of Johannesburg manual on safety, one can read about best practices and maintenance of palisade fencing, such as not growing vegetation in front of palisades as this allows criminals to make an unseen breach.
