Electric fences – a concise history
Alarm bells, water wheels and science fiction novels
The history of electric fences dates back approximately one hundred and fifty years, to the late nineteenth century, although somewhat earlier than that an American publication of 1832 toyed with the idea of using an electrified fence to defend an area. Approximately fifty years later in 1886, an American inventor took out a U.S. patent for a device combining an alarm bell and telephone with an electric fence spanning some thirty miles (just under fifty kilometres). Deriving its electrical power from only a waterwheel, this idea (ingenious as it was, for its time) did not in the end prove to be successful. Two years later in 1888, the first electric fence as such was installed and used in Texas USA, with the aim of reducing the typical number of injuries caused to livestock by the more primitive and harsh solution of barbed wire. However, a degree of scepticism from cowboys towards the new invention meant that this ‘new fangled’ device was not readily accepted, either. In fact, some novels of the time, which were published even as late as 1889, still mentioned electric fences purely as a fictional idea.
Fiction becomes Texan reality – with military use later
From the realms of fiction and one initial installation, however, electric fences became a reality in the Russian-Japanese conflict at Port Arthur in Korea. This involved a siege between 1904 and 1906 and electric fences were improvised for military and defensive purposes. Continuing with the theme of their use by the military, it was during the First World War (1914-1918) that German forces installed a number of electrified fences which were infamously dubbed the ‘wire of death’, used to delineate the Belgian and Dutch borders. Charged with several thousand volts, these fences were designed with the potential to kill – human fatalities were estimated at some three thousand, in addition to many livestock. For the more benign objective of controlling animals, a New Zealand inventor, Bill Gallagher, invented an early application using a trembler induction coil from a car and other bits and pieces from a Meccano set to construct an electric fence to stop his horse from scratching itself against his car, thus causing damage. This same inventor later set up a company to further develop the somewhat improvised contraption into a commercial design, typical fence lengths of between two and three hundred metres to a few kilometres.
New Zealand innovation – improved electrical components and materials
During the late 1930s, emerging public safety issues and concerns about the newly emerging electric fences were considered at length, and began to be controlled more by regulations. In the 1960s, a different New Zealand inventor named Dough Phillips patented a new type of design using capacitor discharge, thus extending the feasible deign length of the fence and at the same time reducing its cost. This was duly patented using plastic insulators for flexibility and durability (instead of the previous porcelain) and similar systems continue to be used in agricultural electric fences today. Early fence charging devices used alternating current (AC) with a transformer and a mechanically operated switch, giving long pulses and sometimes of unpredictable voltages. As might be expected, these mechanical switches frequently failed, so later systems made use of solid state (transistor) circuitry instead of manual switching components. For a period, some types of fence energisers gave longer outputs. Nicknamed ‘weed burners’, this variant became known for causing fires in hot, dry weather and it was for this reason that their popularity reduced.
Further modern developments: ropes and insulators
Over recent years, there have been some significant improvements including polyethylene insulators, which last longer and are cheaper, along with the electrical design of the energizing units which are also called a fencer or energiser. Modern fence chargers use low impedance circuitry, in which a capacitor is charged by a solid-state circuit. If an animal (or a person) comes into contact with the fence, the charge is released by a thyristor. This is an electronic component which can be thought of as an automatic switch so the voltage is more controlled, and the shock pulse is much shorter – typically just a few milliseconds. Fences can be powered by batteries and solar panels; if a fence is in good condition, such batteries can last many weeks depending on fence length. Woven rope-like material containing conducting wires has also been developed. Electric fences are used primarily to stop livestock from escaping or from wandering onto farmland and damaging crops. Although the majority of electric fences today are used for animal control in this way, other applications include prisons, military bases and other protected installations. Here, the aim is to maintain security, or to stop people crossing a borderline or other physical limit. The voltage delivered can be varied and may be selected to cause discomfort or in security applications, incapacitating or lethal. Finally, probably due to their intrinsic risks, there have also been legislative changes and regulations in some countries regarding the construction and use of electric fences.