How an Electric Dog Fence Works
Electric Dog Fences: The Basics
All electric dog fences have two parts, an active part and an inactive part. The active part (red in the drawings above) consists of the positive terminal on the electric fence charger, the insulated electric fence wire connecting the electric fence charger's positive terminal to the conductor (wire, polywire, etc.), and the actively charged conductor that runs along the fence. The inactive or "neutral" part (blue and green in the drawings) consists of the negative terminal on the electric fence charger and everything connected to it. In the traditional setup with adequate soil moisture (see the left-hand drawing), the neutral elements are the charger’s negative terminal, a wire leading over to the ground rod, the ground rod itself, and moisture in the soil lying between the ground rod and the fence.
The target animal gets a shock when it unsuspectingly provides a bridge between these two systems. That is, when it touches the active wire a charge passes from the active wire through the animal's body, through its feet, and out its feet into the water in the ground (dry soil cannot carry a charge but water can). Using this water, the charge travels over to the ground rod, up the ground rod, along the ground rod wire, and over to the negative terminal on the charger, thereby completing the circuit.
But suppose there is no water or extremely little water in the ground, as often happens in parched regions. Then the animal will not get a shock, because there is nothing to carry the charge from its feet over to the ground rod. The same thing happens in deeply frozen ground, because ice in contrast to liquid water cannot carry a charge.
In both these cases, something must be done to remedy the situation or the electric fence won't work. One's first impulse is to get a more powerful electric fence charger or perhaps increase the number of electric fence ground rods. However, these are not ideal remedies. They may improve matters, but they don't get to the heart of the trouble. The best answer, and the only one if the trouble is really bad, is to replace the absent or frozen soil moisture with something else.
Suppose, for example, that you string certain conductors on the electric fence (green in the right-hand drawing) that are not charged, because they are not connected to the charger's positive terminal. Instead they are connected to the charger's negative terminal, and things are arranged so that they do not touch any active conductor. Then, when the animal comes along and touches an active and inactive wire at the same time it gets a shock—with the charge passing from the active wire through the animal to the negative wire and over to the charger's negative terminal, thereby completing the circuit.
Strengths and Weakness of Electric Dog Fences
Pure electric fences are a bit like radio fences in that they present a mostly psychological barrier to the target animal. However, as the posts get stronger and closer, and as the distance between the wires diminishes, these fences take on more of a physical quality, with the result that their effectiveness increases. Taking this one step further, barrier fences can be reinforced by electric fences—a combination of systems that works well to keep dogs from digging under of clambering over the barrier fence (see electrifying a barrier fence).
While the whole spectrum of electric fences can be highly effective when they are working, they also need a watchful eye and careful maintenance. They can get struck by lightning; the charger can stop working; necessary connections can get disconnected; and weeds or falling branches can create an electrical path to the ground—a path eagerly followed by enough electrons to stop your fence from working. You cannot monitor things with an ordinary volt-meter, because it cannot accurately read the high pulsed voltages produced by the fence charger; but periodic surveillance with a simple and affordable fence tester (such as products 04-01 and 04-02) will reveal such problems—and once revealed they are relatively easy to correct.