Electric Fence Inspection

by Nick Gromicko, CMI®
Electric fences are a "fear" barrier that use electric shock to delineate a boundary and discourage animals and people from crossing it. Primarily, they are used to protect livestock and domestic pets by preventing them from leaving a sanctioned area and by deterring predators from entering the area.
An effective electric fence involves the interconnection of the following four components:
  • The energizer turns low-voltage battery power, household current, or converted sunlight into a high-voltage electric shock.A solar-powered electric fence
  • The conductor is the wire that transmits the energizer’s shock to the animal or person who touches it. This is usually galvanized or aluminum-coated steel wire, or poly-tape or poly-rope wire. Manufactured in a number of configurations, all “poly” wires contain tiny stainless steel or copper wires woven into the synthetic fabric, enabling them to conduct electricity.
  • The post supports the conductor at the desired height, while the insulator prevents the electricity in the wire from leaking into the ground through the post. Some posts are non-conductive and thus do not require an insulator.
  • The ground is typically composed of metal rods driven into the soil near the energizer and are connected to it by a wire. A complete circuit occurs when an animal or person touches the conductor, allowing electricity to flow from the conductor through their body and into the soil, where moisture carries the current to the ground rods and back into the energizer. The absence of a ground circuit is how a bird can casually rest on a high-voltage power line.

In general, an electric fence should be supplied with only enough power to startle -- not injure -- so that an animal that brushes up against the fence will recoil but not suffer electrical burns or permanent injury. The feeling should be similar to the stinging sensation of a snapped rubber band. Exceptions are made for prisons, military installations and vital utility stations to discourage escapes and vandalism attempts.

Fences that are too strongly electrified for their application, whether by accident or design, are a serious safety hazard. Aside from unnecessarily and inhumanely exposing farm animals or pets to unsafe shocks, homeowners must consider the inherent dangers that these fences may pose to firefighters, police and trespassers. Note that “trespasser” can refer to an innocent child, such as a 6-year-old Texas girl who was killed instantly when she touched a neighbor’s electric fence. The investigating police captain said the amperage was far too high, “enough to power half of a house. She didn’t have time to scream for help, close her eyes... nothing,” according to KLTV. The owner of the fence pleaded guilty to criminally negligent homicide.

Other cases of over-powered fences abound; an elderly New York woman was killed when she tried to free her pet from an electric fence. The voltage was too high and the fence lacked a regulator to pulse the shock. A Denver, Colorado, man even succumbed to his own fence –- a DIY project designed to keep his dogs in the yard, yet set to deliver lethal voltage, and designed without a regulator. (He did, however, receive a posthumous Darwin Award for his efforts.)

A few additional tips:

  • Lightning is one of the main causes of electric fence fires and controller malfunction. Use the following strategies to minimize lightning dangers:
    • Disconnect the controller from the fence line and power source before a storm is expected.
    • Install a lightning diverter (commonly referred to as a lightning arrestor) between the fence and the controller. This will divert a lightning strike’s electricity to the earth before it does any damage to the controller.
    • Install a surge suppressor to protect the controller on the utility side. The suppressor is plugged into the outlet and the controller is plugged into the suppressor.This African Rock Snake won't be eating any more sheep
    • Install a cutoff switch as a quick way to disconnect the fence from the controller without actually getting near the fence. This switch also allows the fence to be conveniently turned off while it’s being worked on.
  • The energizer must be sized properly for the type of animal to be contained within the perimeter. Extra voltage may be required for sheep, for instance, as their thick wool (especially in the winter) is an effective insulator against shock. Their burned wool can wrap around the conductor and further nullify the shock against the rest of the herd, as the other sheep follow the first sheep into the road, a neighbor’s yard, or into a waiting pack of hungry coyotes. Of course, the size of the animal is also a factor, as a small dog will not need as much of a jolt as a horse. The length of the fence must be considered, too, as the potency of the shock will dissipate if it's forced to travel too far from the conductor.

  • Poor grounding weakens the electric shock and can interfere with radios, telephones and televisions. Multiple ground rods should be installed, each 6 to 8 feet long, and attached with adequate ground clamps. In very dry or cold climates, a ground wire may be needed to run parallel to the hot wire so that the system does not depend on insulating dry or frozen soil.

  • Poly-tape and poly-rope give greater tensile strength and are useful in high-voltage applications, although most electric fences are made from aluminum or galvanized steel. Never use more than one type of metal, as corrosion can occur when two different metals are hooked together, weakening the connection and the whole electric fence.

  • Fences should be equipped with warning signs that alert passersby to their danger, as it isn’t always obvious that a fence is electrified. In one bizarre instance that was conveniently captured by a security camera, a man was knocked unconscious when he urinated on a fence that he did not realize was electrified.

  • Equip the fence with a light that shines when the fence is not operational. This way, fence operators can quickly fix a malfunction before penned animals become wise to the failing. Inspectors can tell if a fence is working by touching the metal end of a long screwdriver to the conductor while holding the plastic, insulated end. An active fence should create a visible, audible arc. Do not use an uninsulated item for this purpose, such as a blade of grass.

  • Never touch a fence that may be electrified (or any live circuits of hazardous voltage) with two hands, as this will allow the current to travel through the heart and lungs. Always keep one hand in your pocket so you don’t accidentally touch something that will turn a painful but non-lethal shock into cardiac arrest. 

  • Never electrify barbed-wire fences. It takes little imagination to picture what will happen if electrified barbs become trapped in an animal’s fur.

  • Keep flammable materials far from the electric fence. Small sparks and arcs can easily occur due to weather conditions, lightning strikes, vegetation brushing against the fence, or fence malfunctions.

  • Be sure to purchase high-quality, long-lasting insulators that will not degrade from exposure to ultraviolet light. Cheap insulators will grow weak and eventually shatter.

  • Plant fence posts solidly, at least 2 feet in the ground in solid earth or concrete, especially if you plan to contain large animals. Space the posts far enough apart that the wires have room to bend, rather than forcing undue stress on the posts and insulators. 

In summary, electric fences are useful and practical deterrents in a number of applications, both commercial and residential.  But improperly maintained or designed electric fences can seriously injure or kill animals and humans.

Take InterNACHI's free, online How to Perform Residential Electrical Inspections course.