How Electric Fences Work

Once snubbed in equestrian circles, electric fences now come in forms well suited for horse properties. Here's a look at how they work. From EQUUS magazine.
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Once snubbed in equestrian circles, electric fences now come in forms well suited for horse properties. Here's a look at how they work. From EQUUS magazine.

Time was, everyone who owned livestock knew the basic rules: cattle and sheep needed to be enclosed with electric wire, but horses were best off behind wood planks or poles. And for good reason: Horses need to see their barriers, or they run into them and get tangled up - or worse. The thin stiff wires used in earlier electric fences were nearly invisible to equine eyes.

Nowadays, though, new types of electric fences are on the market. Designed in wider braids, ribbons or bands for greater visibility, modern electric fencing is the choice of a growing number of horse-keepers, who find that many of the old beliefs - that electric fencing is painful, unsafe, expensive, unreliable and difficult to maintain - are no longer true.

Safety is, of course, the foremost concern in any fencing decision. But what exactly constitutes a safe fence can become a complicated question. In some ways, horses are among the easiest animals to keep secure: If they have all the food, water, shelter and friends they want, most horses aren't likely to try to leave their familiar surroundings. On the other hand, horse do pose a special challenge: short of a 10-foot concrete wall, not much will hold in a 1,200-pound animal who's determined or frightened-enough to escape.

In general, the stronger the fence, the less likely the horse is to escape. Yet the stronger the fence, the more likely the horse is to injure himself during a panic. Many serious wounds have resulted from horses ramming and splintering wooden fences or running into lacerating wire or unyielding posts. All of which has contributed to the growing popularity of electric fences among horse-keepers. Electric fences offer a barrier that horses respect, and the newer materials, which are designed to flex under pressure, are less likely to injure a determined kamikaze or Houdini.

Learning a bit about how electric fences work, as well as how to use and maintain one, will help you make an informed decision about whether electrified fencing is right for your property.

One-touch serviceTouch an electric fence once and you'll know why it works; it's not very painful -- about the equivalent of a sharp slap -- but you'll remember the sensation, and you won't want to repeat it anytime soon. Horses, too, learn quickly that they don't want to bump, push through, rub against or chew on electric fences.

How an electric fence works isn't too complicated either. Every electric fence includes three basic components:

  • A wire fence carries an electric charge. This is the "hot," above-ground part of the system.
  • An energizer (also known as a charger) pushes power through the fence. To meet safety standards, most systems deliver power in a series of pulses, usually about one per second. That time between pulses helps the animal to break free of the fence. (A continuous current might cause the animal to "lock on," unable to let go.)
  • A ground system, usually a series of metal rods sunk into the earth and connected to the energizer via a ground wire, waits dormant until the fence is touched by any animal that is also in contact with the ground. The ground system attracts the charge through the animal and returns the current to the energizer through the ground wire. The system operates on a very simple principle: Electricity will only travel through a closed circuit. The fence wire, energizer and ground rods are three parts of a circuit waiting to be closed; when a horse touches the wire, he closes the gap, and -- assuming nothing blocks or impedes the flow of electricity -- a surge of current will travel through him from the fence to the rods planted in the ground. Once the circuit is complete, the animal will feel a shock that is likely to discourage him from touching the fence again.The strength of the shock depends on several variables, but two basic terms in combination will determine the strength of a fence:
    Voltage, measured in volts (V) or kilovolts (kV), is the force or pressure with which a current flows through the circuit. The higher the voltage, the farther the current can travel through the wire before resistance slows it down; higher voltage also causes a stronger "startle" from the shock. Amperage (amps) measures the magnitude or strength of the current. The higher the amperage, the greater the sensation the current will cause when it enters a body. The level of unpleasantness produced by a shock depends more on the amperage -- or size -- than on the voltage -- or pressure -- of a current. One easy way to think of it is to imagine the power of water rushing through a fire hose. If you were on the receiving end of a blast of water that raced through a one-inch-thick hose at 100 mph, you'd feel like you'd been struck by a major-league fastball; the impact would probably knock you down. Reduce the size of the hose to an eighth of an inch thick, and you'd feel a sharp sting -- enough to catch your attention -- but no serious injury. However, slow the water down to only 1 mph, and even a very large hose would do you no harm. Likewise, a large charge traveling at a very slow rate can actually produce a fairly mild shock. For instance, when you walk across a carpet and touch a doorknob, the shock you feel may be as much as 5,000 volts, but it has a very low amperage. At the opposite extreme, an electric chair operates on only about 2,000 volts, but the high amperage is enough to kill. With an electric fence, the goal is to sting or startle the animal without causing harm, so electric fences operate with low amperage and higher voltage. As long as the amperage is adequate, horses can be controlled with as little as 2,000 volts, but to make the fence more memorable and easier to maintain, a minimum of 3,000 volts is recommended. Animals are the intended targets of electric fences, but anything else that comes in contact with both fence and ground will also complete the circuit. Very small items, such as blades of grass, allow a small amount of power to travel from the fence to the ground rods, but not enough to drain the entire system. (It's like a series of small holes in the fire hose, allowing some of the water to dribble away, weakening the pressure in the hose.) A short circuit occurs when an object, such as a fallen tree limb, reroutes all of the power from the fence to the ground system. Beyond the tree limb, the charge left in the fence is reduced to zero. This article first appeared in the April, 2001 issue of EQUUS magazine.