Electric fence
Encyclopedia
Electric shock
Electric Shock of a body with any source of electricity that causes a sufficient current through the skin, muscles or hair. Typically, the expression is used to denote an unwanted exposure to electricity, hence the effects are considered undesirable....
s to deter animals or people from crossing a boundary. The voltage of the shock may have effects ranging from uncomfortable, to painful or even lethal. Most electric fencing is used today for agricultural fencing
Agricultural fencing
In agriculture, fences are used to keep animals in or out of an area. They can be made from a wide variety of materials, depending on terrain, location and animals to be confined...
and other forms of animal control purposes, though it is frequently used to enhance security of sensitive areas, and there exist places where lethal voltages are used.
Design and function
Electrical network
An electrical network is an interconnection of electrical elements such as resistors, inductors, capacitors, transmission lines, voltage sources, current sources and switches. An electrical circuit is a special type of network, one that has a closed loop giving a return path for the current...
when touched by a person or animal. A component called a power energizer converts power into a brief high voltage
High voltage
The term high voltage characterizes electrical circuits in which the voltage used is the cause of particular safety concerns and insulation requirements...
pulse. One terminal of the power energizer releases an 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
Ground (electricity)
In electrical engineering, ground or earth may be the reference point in an electrical circuit from which other voltages are measured, or a common return path for electric current, or a direct physical connection to the Earth....
. 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 uncomfortable electric shock
Electric shock
Electric Shock of a body with any source of electricity that causes a sufficient current through the skin, muscles or hair. Typically, the expression is used to denote an unwanted exposure to electricity, hence the effects are considered undesirable....
. The effects of the 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; it can range from barely noticeable to uncomfortable, painful or for some fences even lethal.
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."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
Thyristor
A thyristor is a solid-state semiconductor device with four layers of alternating N and P-type material. They act as bistable switches, conducting when their gate receives a current trigger, and continue to conduct while they are forward biased .Some sources define silicon controlled rectifiers and...
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.
Depending on the area to be fenced and remoteness of its location, fence energizers may be hooked into a permanent electrical circuit, may be run by lead-acid
Lead-acid battery
Lead–acid batteries, invented in 1859 by French physicist Gaston Planté, are the oldest type of rechargeable battery. Despite having a very low energy-to-weight ratio and a low energy-to-volume ratio, their ability to supply high surge currents means that the cells maintain a relatively large...
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 fence may last for several weeks on a single charge. For shorter periods dry cell
Dry Cell
-Dry Cell's formation:Part of the band formed in 1998 when guitarist Danny Hartwell and drummer Brandon Brown met at the Ratt Show on the Sunset Strip. They later met up with then-vocalist Judd Gruenbaum. The original name of the band was "Beyond Control"....
batteries may be used. Some energizers are capable of being powered by more than one source.
Fencing materials
Smooth steel wire is the material most often used for electric fence, ranging from a fine thin wire used as a single line to thicker, high-tensile (HT) wire. Less often, woven wire or barbed wireBarbed wire
Barbed wire, also known as barb wire , is a type of fencing wire constructed with sharp edges or points arranged at intervals along the strand. It is used to construct inexpensive fences and is used atop walls surrounding secured property...
fences can be electrified, though such practices create a more hazardous fence, particularly if a person or animal becomes caught by the fencing material (electrified barbed wire is illegal in some areas). Synthetic webbing and rope-like fencing materials woven with fine conducting wires (usually of stainless steel
Stainless steel
In metallurgy, stainless steel, also known as inox steel or inox from French "inoxydable", is defined as a steel alloy with a minimum of 10.5 or 11% chromium content by mass....
) have become available the last 15 to 20 years, and are particularly useful for areas requiring additional visibility or as 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.
History
Jules Verne's "20,000 Leagues Under the Sea", described the use of electrification of a structure as a defensive weapon, in 1870. The concept of the electric fence was also described in Mark TwainMark Twain
Samuel Langhorne Clemens , better known by his pen name Mark Twain, was an American author and humorist...
's 1889 A Connecticut Yankee in King Arthur's Court
A Connecticut Yankee in King Arthur's Court
A Connecticut Yankee in King Arthur's Court is an 1889 novel by American humorist and writer Mark Twain. The book was originally titled A Yankee in King Arthur's Court...
, as a defensive weapon.
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 energized by a water wheel in Texas in 1888, but it was not successful.
In 1906, the Russian army improvised electric fences during the Russo-Japanese War
Russo-Japanese War
The Russo-Japanese War was "the first great war of the 20th century." It grew out of rival imperial ambitions of the Russian Empire and Japanese Empire over Manchuria and Korea...
at Port Arthur. In 1915, during World War I, the German army electrified fences along the border between Belgium and the Netherlands to prevent unathorized movement of people across the border. The fences covered 300 kilometres and consisted of several strands of copper wire, backed with barbed wire, and energized to several thousand volts. An estimated 3000 human fatalities were caused by the fence, as well as destruction of livestock.
Electric fences were used to control livestock
Livestock
Livestock refers to one or more domesticated animals raised in an agricultural setting to produce commodities such as food, fiber and labor. The term "livestock" as used in this article does not include poultry or farmed fish; however the inclusion of these, especially poultry, within the meaning...
in the United States in the early 1930s, and electric fencing technology developed in both the United States and New Zealand
New Zealand
New Zealand is an island country in the south-western Pacific Ocean comprising two main landmasses and numerous smaller islands. The country is situated some east of Australia across the Tasman Sea, and roughly south of the Pacific island nations of New Caledonia, Fiji, and Tonga...
.
An early application of the electric fence was developed in 1936–1937 by New Zealand
New Zealand
New Zealand is an island country in the south-western Pacific Ocean comprising two main landmasses and numerous smaller islands. The country is situated some east of Australia across the Tasman Sea, and roughly south of the Pacific island nations of New Caledonia, Fiji, and Tonga...
inventor William "Bill" Gallagher Sr
Gallagher Group Limited
The Gallagher Group is a company focused on the animal management systems and security system markets, and is based in Hamilton, New Zealand. Established in 1938, the Group continues to be owned by the Gallagher family, and has a network of distribution channels in more than 130 countries.The...
. Built from a car's ignition coil and a magneto
Magneto
A magneto is a type of electrical generator.Magneto may also refer to:* Magneto , permanent magnetic alternating current rotary generator* ignition magneto, magnetos on internal combustion engines...
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 meters to 35 km (~20 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 to replace ceramic with plastic insulators. A variety of plastic insulators are now used on farms throughout the world today.
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 June 23, 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.
Electric fences have improved significantly over the years. Improvements include:
- PolyethylenePolyethylenePolyethylene or polythene is the most widely used plastic, with an annual production of approximately 80 million metric tons...
insulatorElectrical insulationthumb|250px|[[Coaxial Cable]] with dielectric insulator supporting a central coreThis article refers to electrical insulation. For insulation of heat, see Thermal insulation...
s replacing porcelainPorcelainPorcelain is a ceramic material made by heating raw materials, generally including clay in the form of kaolin, in a kiln to temperatures between and...
insulators, beginning in the 1960s. Polyethylene is much cheaper than porcelain and is less breakable. - Improvements in electrical design of the fence energizer, often called a "charger" (USA) or "fencer" (UK).
- Changes in laws. In some jurisdictions, certain types of electrical outputs for fences were unlawful until the 1950s or 1960s. In other areas, signage requirements and other restrictions limited usability. Many US cities continue to have outdated laws prohibiting electric fences to prevent agricultural fences from entering the city. Houston, for example, changed their ordinance that prohibited electric fencing in 2008.
- Introduction of high tensile (HT) steel fence wire in the 1970s in New Zealand and in the 1980s in the United States
- Introduction of synthetic webbing and rope-like fencing materials woven with fine conducting wires.
- Design of moveable fence components, such as TumblewheelTumblewheelThe tumblewheel is a moveable fence post used to create mobile one-wire fences for the purpose of rotational grazing. Typically used for electric fencing, the insulated central hub enables the line to maintain power while the fence is being moved....
.
Agriculture
Permanent electric fencing is used in many agricultural areas, as construction of electric fences can be much cheaper and faster than conventional fences (it uses plain wire and much lighter construction, as the fence does not need to physically restrain animals). The risk of injury to livestock (particularly horseHorse
The horse is one of two extant subspecies of Equus ferus, or the wild horse. It is a single-hooved mammal belonging to the taxonomic family Equidae. The horse has evolved over the past 45 to 55 million years from a small multi-toed creature into the large, single-toed animal of today...
s) is lower compared to fences made of barbed wire
Barbed wire
Barbed wire, also known as barb wire , is a type of fencing wire constructed with sharp edges or points arranged at intervals along the strand. It is used to construct inexpensive fences and is used atop walls surrounding secured property...
or certain types of woven wire with large openings that can entangle the feet.
Its disadvantages include the potential for the entire fence to be disabled due to a break in the conducting wire, shorting out if the conducting wire contacts any non-electrified that may make up the rest of the fence, power failure, or forced disconnection due to the risk of fires starting by dry vegetation touching an electrified wire. Other disadvantages can be lack of visibility and the potential to shock an unsuspecting human passer-by who might accidentally touch or brush the fence.
Many fences are made entirely of standard smooth or high-tensile wire, though 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.
Conventional agricultural fencing
Agricultural fencing
In agriculture, fences are used to keep animals in or out of an area. They can be made from a wide variety of materials, depending on terrain, location and animals to be confined...
of any type may be strengthened by the addition of a single electric line mounted on insulators attached to the top or front of the fence. A similar wire mounted close to the ground may be used to prevent pig
Pig
A pig is any of the animals in the genus Sus, within the Suidae family of even-toed ungulates. Pigs include the domestic pig, its ancestor the wild boar, and several other wild relatives...
s from excavating beneath other fencing. Substandard conventional fencing can also be made temporarily usable until proper repairs are made by the addition of a single electric line set on a "stand-off" insulator.
Managed intensive grazing
Management Intensive Rotational Grazing is a system of grazing in which ruminant and non-ruminant herds are regularly and systematically moved to fresh pasture with the intent to maximize the quality and quantity of forage growth. MIRG can be used with cattle, sheep, goats, pigs, chickens, ducks...
(also known as rotational or "strip" grazing). It is also popular in some places for confining horses and pack animals
Packhorse
.A packhorse or pack horse refers generally to an equid such as a horse, mule, donkey or pony used for carrying goods on their backs, usually carried in sidebags or panniers. Typically packhorses are used to cross difficult terrain, where the absence of roads prevents the use of wheeled vehicles. ...
overnight when trail riding
Trail riding
Trail riding sometimes called horse or pony trekking is riding outdoors on natural trails and roads as opposed to riding in an enclosed area such as a riding arena. The term may encompass those who travel on horses, on mountain bikes, or on motorcycles and other motorized all-terrain vehicles...
, hunting
Hunting
Hunting is the practice of pursuing any living thing, usually wildlife, for food, recreation, or trade. In present-day use, the term refers to lawful hunting, as distinguished from poaching, which is the killing, trapping or capture of the hunted species contrary to applicable law...
, or at competitions such as endurance riding
Endurance riding
Endurance riding is an equestrian sport based on controlled long-distance races. It is one of the international competitions recognized by the FEI. There are endurance rides worldwide....
and competitive trail riding
Competitive trail riding
Competitive Trail Riding is an equestrian sport where riders cover a marked trail for a distance that is usually between 15 and 40 miles per day. Some rides are only one day long, others may run as long as three days....
. Typically, one or more strands of wire, synthetic tape or cord are mounted on metal or plastic posts with stakes at the bottom, designed to be driven into the ground by foot. For a hand-tightened temporary fence of electrified rope or web in a small area, these are usually spaced at no more than 12 to 15 feet (about 3 metres) to prevent the fencing material from sagging and touching the ground. Larger areas where tools are used to stretch wire may be able to set step-in posts at larger distances without risk that the fencing material will sag.
With temporary electric fencing, a large area can be fenced off in a short period of time. Temporary fencing that is intended to be left in place for several weeks or months may be given additional support by the use of steel T posts (which are quickly pounded in with hand tools and unearthed with relative ease using a leverage device) to help keep the fence upright, particularly at corners. Livestock owners using rotational grazing in set patterns that are similar from one year to the next may permanently drive a few permanent wood fence posts in strategic locations.
Portable fence energizers are made for temporary fencing, powered solely by batteries, or by a battery kept charged by a small solar panel. Rapid laying-out and removal of multiple-strand temporary electric fencing over a large area may be done using a set of reels mounted on a tractor
Tractor
A tractor is a vehicle specifically designed to deliver a high tractive effort at slow speeds, for the purposes of hauling a trailer or machinery used in agriculture or construction...
or all-terrain vehicle
All-terrain vehicle
An all-terrain vehicle , also known as a quad, quad bike, three wheeler, or four wheeler, is defined by the American National Standards Institute as a vehicle that travels on low pressure tires, with a seat that is straddled by the operator, along with handlebars for steering control...
.
For sheep, poultry
Poultry
Poultry are domesticated birds kept by humans for the purpose of producing eggs, meat, and/or feathers. These most typically are members of the superorder Galloanserae , especially the order Galliformes and the family Anatidae , commonly known as "waterfowl"...
, and other smaller animals, plastic electric netting may be mounted on insulating stakes – this is also effective at keeping out some predators such as foxes.
In practice, once most animals have learned of the unpleasant consequences of touching the fence they tend to avoid it for considerable periods even when it is inactive. However, some animals learn to avoid the shock, either by running under the fence quickly between pulses, or by pushing other individuals through the fence. Animals with thick woolly coats (such as sheep or Highland cattle
Highland cattle
Highland cattle or kyloe are a Scottish breed of beef cattle with long horns and long wavy coats which are coloured black, brindled, red, yellow or dun....
) may learn to push through the fence themselves, using their coats as electrical insulation. Some animals also learn to recognize the slight clicking sound made by some electric fences and thus can sense when the fence is off.
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, keeping wild boarBoar
Wild boar, also wild pig, is a species of the pig genus Sus, part of the biological family Suidae. The species includes many subspecies. It is the wild ancestor of the domestic pig, an animal with which it freely hybridises...
from raiding crops, and preventing geese from soiling areas used by people. Electric fencing has been extensively used in environmental situations reducing the conflict between elephants or other animals and humans in Africa and Asia.
Non-lethal fence
Non-lethal electric fences are used to prevent trespass by both private and government-sector bodies. 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.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.In 1915, during World War I
World War I
World War I , which was predominantly called the World War or the Great War from its occurrence until 1939, and the First World War or World War I thereafter, was a major war centred in Europe that began on 28 July 1914 and lasted until 11 November 1918...
, the German
Germany
Germany , officially the Federal Republic of Germany , is a federal parliamentary republic in Europe. The country consists of 16 states while the capital and largest city is Berlin. Germany covers an area of 357,021 km2 and has a largely temperate seasonal climate...
occupiers of Belgium
Belgium
Belgium , officially the Kingdom of Belgium, is a federal state in Western Europe. It is a founding member of the European Union and hosts the EU's headquarters, and those of several other major international organisations such as NATO.Belgium is also a member of, or affiliated to, many...
closed off the border with neutral Netherlands
Netherlands
The Netherlands is a constituent country of the Kingdom of the Netherlands, located mainly in North-West Europe and with several islands in the Caribbean. Mainland Netherlands borders the North Sea to the north and west, Belgium to the south, and Germany to the east, and shares maritime borders...
, using a 300 km electric fence running from Vaals
Vaals
Vaals is a town in the extreme southeastern part of the Dutch province of Limburg, which in its turn finds itself in the southeastern part of the Netherlands....
to Scheldt
Scheldt
The Scheldt is a 350 km long river in northern France, western Belgium and the southwestern part of the Netherlands...
. Germany also erected a similar fence to isolate thirteen Alsatian villages from Switzerland.
Electric fences were used to guard the concentration camps of Nazi Germany
Nazi Germany
Nazi Germany , also known as the Third Reich , but officially called German Reich from 1933 to 1943 and Greater German Reich from 26 June 1943 onward, is the name commonly used to refer to the state of Germany from 1933 to 1945, when it was a totalitarian dictatorship ruled by...
during World War II
World War II
World War II, or the Second World War , was a global conflict lasting from 1939 to 1945, involving most of the world's nations—including all of the great powers—eventually forming two opposing military alliances: the Allies and the Axis...
, where potentially lethal voltages and currents were employed, continuously rather than in pulses. Some prisoners used the electric barbed wire fence to commit suicide.
During the Algerian War the French erected the electrified Morice Line
Morice Line
The Morice Line was a defensive line constructed in the 1950s and finished in September 1957. It was built to prevent Algerian FLN guerrillas from entering the French colony of Algeria from Tunisia and Morocco. It was named after the French Minister of Defence André Morice.-Design:The center of the...
.
Sections of the inner German border were lined with a 3 m (10 ft) high electric fence to deter potential defectors from East Germany.
Electric fences continue to be used in similar fashion at some high-security prisons and certain other installations to this day. Typically a nonelectric fence is constructed on either side of such an installation, or the deadly current is carried out of casual reach atop a wall.
North Korea
North Korea
The Democratic People’s Republic of Korea , , is a country in East Asia, occupying the northern half of the Korean Peninsula. Its capital and largest city is Pyongyang. The Korean Demilitarized Zone serves as the buffer zone between North Korea and South Korea...
uses electric fences to seal off parts of its border
Korean Demilitarized Zone
The Korean Demilitarized Zone is a strip of land running across the Korean Peninsula that serves as a buffer zone between North and South Korea. The DMZ cuts the Korean Peninsula roughly in half, crossing the 38th parallel on an angle, with the west end of the DMZ lying south of the parallel and...
with South Korea
South Korea
The Republic of Korea , , is a sovereign state in East Asia, located on the southern portion of the Korean Peninsula. It is neighbored by the People's Republic of China to the west, Japan to the east, North Korea to the north, and the East China Sea and Republic of China to the south...
.
Other uses
Recent innovations include electrical fence monitoring for intruder detection as opposed to providing an electric shock to discourage entry. It can be used in addition to or as substitute for a host of other fence monitoring systems.Buried electric fences
Pet fence
A pet fence or fenceless boundary is an electronic system designed to keep a pet or other domestic animal within a set of predefined boundaries without the use of a physical barrier.-Technology:...
(also called "invisible fences" or "electronic fences") are sometimes used to contain dog
Dog
The domestic dog is a domesticated form of the gray wolf, a member of the Canidae family of the order Carnivora. The term is used for both feral and pet varieties. The dog may have been the first animal to be domesticated, and has been the most widely kept working, hunting, and companion animal in...
s or livestock. The buried wire radiates a weak radio signal, which is detected by a collar worn by the animal. The collar emits a warning noise near the wire, but if this is ignored, produces a mild shock. Humans and other animals are unaware of the buried line. In a similar system, the collar uses GPS signals to determine proximity to a predetermined "virtual fence" without a physical installation.
Interference and unwanted effects
Poorly designed or badly maintained electric fences can create sufficient electromagnetic interferenceElectromagnetic interference
Electromagnetic interference is disturbance that affects an electrical circuit due to either electromagnetic induction or electromagnetic radiation emitted from an external source. The disturbance may interrupt, obstruct, or otherwise degrade or limit the effective performance of the circuit...
to cause problems for nearby telephone, radio, and television reception - and has been a particular problem for dial-up Internet users in some rural areas.
External links
- Controlling deer
- Wildlife control at Canadian Airports
- Controlling geese
- Uses in Montana
- Use in prisons
- New Zealand Government advice on electric fence interference
- Telecom New Zealand advice on electric fence interference
- De Draad, Dutch Wikipedia article on the 1915 border fence