Electric fence
An electric fence is a barrier that uses electric shocks to deter humans and animals from crossing a boundary. Most electric fences are used for agricultural purposes and other non-human animal control. They are also commonly used to protect high-security areas such as military installations or prisons, where a potentially lethal voltage may be applied. Virtual electric fences for livestock using GPS technology have also been developed.
Design and function
Electric fences are designed to shock animals or humans if they attempt to cross a boundary. A component called a power energiser converts power into a brief high voltage pulse. One terminal of the power energiser releases an electrical pulse along a connected bare wire approximately once per second. Another terminal is connected to a metal rod implanted in the earth, called a ground or earth rod. An animal touching both the wire and the earth during a pulse would complete an electrical circuit, conducting a pulse, resulting in an electric shock. The effects of a shock depend upon the voltage, the energy of the pulse, the degree of contact between the recipient and the fence and ground, and the route of the current through the body; the severity of the shock can range from barely noticeable to lethal.Fence energisers
Most modern electric fences emit pulses of high voltage at a fixed time interval or use a voltage multiplier to store a high voltage that is applied continuously to the fence except when recharging after a shock.Depending on the fenced area and the remoteness of its location, fence energisers may be hooked into a permanent electrical circuit or run by lead-acid or dry cell batteries or a smaller battery kept charged by a solar panel. The power consumption of a fence in good condition is low, and so a lead-acid battery powering several hundred metres of the fence may last for several weeks on a single charge. Certain energisers have the ability to be powered by multiple sources.
Early alternating current 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, which had the liability of the switch mechanism failing. Later systems replaced this switch with a solid-state circuit. This circuit had 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. Although still available, they have declined in popularity.
Fencing materials
Smooth steel wire is the material most often used for electric fences, ranging from a fine thin wire used as a single line to thicker, high-tensile wire. Less often, woven wire or barbed wire fences can be electrified, though such practices create a more hazardous fence, particularly if an animal becomes caught by the fencing material, causing electrified barbed wire to be made unlawful in some areas. Synthetic webbing and rope-like fencing materials woven with fine conducting wires became available in the late 1990s and are particularly useful for areas requiring additional visibility or temporary fencing.The electrified fence itself must be kept insulated from the earth and from any materials that will conduct electricity and ignite or short out the fence. Fencing must therefore avoid vegetation, and cannot be attached directly to wood or metal posts. Typically, wooden or metal posts are driven into the ground and plastic or porcelain insulators are attached to them, or plastic posts are used. The conducting material is then attached to the posts.
Palisade fences
Electrified palisade fences are usually made from painted mild steel, galvanised steel, stainless steel or aluminium. Typically, these fences are tall and send high voltage electric pulses through the palisade at a frequency of 1 Hz.Palisade electric fences are used in most countries, particularly where there is little vegetation to short-circuit the fence or where the costs of security personnel are high in relation to automated security equipment. The electric pulse is a strong deterrent for criminals, while the palisade fence is mechanically stronger than a typical steel cable electric fence, being able to withstand impact from wildlife, small falling trees and wildfires.
Due to the high levels of crime in South Africa, it is common for residential houses to have perimeter defences. The City of Johannesburg promotes the use of palisade fencing over opaque, usually brick, walls as criminals cannot hide as easily behind the fence. The City of Johannesburg manual on safety describes 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.
Virtual electric fence
In a virtual electric fence system, each animal has a collar with a GPS unit which is set to produce first an audible warning and then a shock as the animal approaches a programmable boundary. Pet fences to control domestic dogs have been used since 1973, and the first system for livestock control was developed by Peck's Invisible Fence Co, now Invisible Fence Inc., in 1987. An early application involved goats and Euphorbia esula. Virtual fencing has been used by the Royal Society for the Protection of Birds in England to control grazing in wild and sensitive landscapes without the need for expensive and visually intrusive fencing. Companies which have developed this technology include the Norwegian Nofence, the Australian Agersens and the American Vence.In many countries such as Switzerland or Austria, virtual electric fences are currently not allowed due to concerns about animal welfare. In 2023 and 2024, industry-funded studies by the Venn Research Association and Agroscope found their effect on goats and cows to be comparable to traditional electric fences.
History
First published in 1832, Chapter 7 of Domestic Manners of the Americans by Fanny Trollope describes an arrangement of wires connected with an electrical machine used to protect a display called "Dorfeuille's Hell" in the Western Museum of natural history in Cincinnati, which she herself invented. Published in 1870, Chapter 22 of Jules Verne's Twenty Thousand Leagues Under the Seas, describes "The Lightning Bolts of Captain Nemo"the use of electrification of a structure as a defensive weapon. Published in 1889, Mark Twain's novel A Connecticut Yankee in King Arthur's Court, uses an electric fence for defensive purposes.David H. Wilson obtained United States Patent 343,939 in 1886, combining protection, an alarm bell, and telephone communications. He constructed an experimental 30-mile electric fence energised by a water wheel in Texas in 1888, which proved successful at keeping cattle separated, but was deemed impractical as a business venture.
In 1905, the Russian army improvised electric fences during the Russo-Japanese War at Port Arthur. In 1915, during World War I, the German army installed the "Wire of Death", an electrified fences along the border between Belgium and the Netherlands to prevent unauthorised movement of people across the border. The fences covered and consisted of several strands of copper wire, backed with barbed wire, and energised to several thousand volts. An estimated 3,000 human fatalities, as well as the destruction of livestock, were caused by the fence.
Electric fences were used to control livestock 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 for livestock control was developed in 1936-1937 by New Zealand inventor Bill Gallagher. Built from a car ignition trembler coil set, Gallagher used the device to keep his horse from scratching itself against his car. Gallagher later started the Gallagher Group 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 metres to, 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". Since then, a variety of plastic insulators are now used on farms throughout the world.
By 1939, public safety concerns in the United States prompted Underwriters' Laboratories to publish a bulletin on electric shock from electric fences, leading to the ANSI/UL standard No. 69 for electric fence controllers.
In 1969, Robert B. Cox, a farmer in Adams County, Iowa, invented an improved electric fence bracket and was issued United States Patent No. 3,516,643 on 23 June 1970. This bracket improved electric fences by keeping the wire high enough above the ground and far enough away from the fence to permit grass and weeds growing beneath the wire to be mowed. The brackets attached to the posts by what may be called a "pivot bind" or "torsion-lock". The weight of the bracket, the attached insulator and the electric wire attached to the insulator bind the bracket to the post.
Improvements
Electric fencing has changed significantly as materials, engineering, and regulations have caught up with practical needs in the field. One of the earliest improvements came in the 1960s, when polyethylene insulators began replacing porcelain. They were cheaper, lighter, and far less likely to break, which made fences easier to build and maintain.The fence energiser, known as a “charger” in the United States and a “fencer” in the United Kingdom, also improved over time. Better electrical design made power delivery more reliable and consistent. At the same time, laws governing electric fences began to shift. In some places, certain electrical outputs were not permitted until the mid twentieth century. Elsewhere, signage rules and other restrictions limited where fences could be used. Many U.S. cities still have older bylaws that prohibit electric fencing to prevent agricultural fences from appearing in urban neighbourhoods, although some have modernized these rules. Houston, Texas, for example, revised its ordinance in 2008.
Further advances followed in materials. High tensile steel wire was introduced in New Zealand in the 1970s and later adopted in the United States in the 1980s, allowing longer runs of fence with fewer posts. New synthetic options also appeared, including webbing and rope-style fencing woven with fine conducting wires. These designs improved visibility and flexibility without sacrificing electrical performance.
More recent designs have focused on adaptability. Moveable fence components, such as the Tumble-wheel, made temporary single-wire fences easier to use for rotational grazing. The insulated central hub allows the fence to stay powered even while it is being moved, reflecting a broader shift toward flexible and management-friendly electric fencing systems.