Security Fences
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There have been electric fences used around the world for the last hundred years. They have been used effectively to contain all types of livestock, from cattle and horses to wild deer and antelope. They have also been effective in protecting crops from nuisance animal pests of all types, even elephants.
Most people that have lived in the country or provinces have had experience with electric fences of one type or another. You jump over, or very carefully crawl under the “hot” wire to cross the fence.
This is not much of a security device, even though we’re terrified of touching the electrified wire.
Why? The fence described is designed for effective cost and is primarily designed to keep livestock safely contained. Even a half-ton bull will stop short of the “hot” wire.
So let’s design a fence to keep out humans that think, that climb, that cut wires, that crawl under, that jump over, that short out the electrified wire, and generally are more difficult to deal with.
We know that the human trespasser is aware of, and deathly afraid, of touching the hot wire and getting a nasty shock.
So we design the fence so the human cannot go over, under, or through without getting badly shocked.
It’s only been the last few years that high voltage electric fences have been commonly used for security.
There are several differences in design that make a standard electric fence work for security.
1. The first difference is the spacing of the strands. Six inches apart, or less, is considered the most effective spacing. The bottom strand should be even closer to the wall or footer, as close as three inches. The reasons for this are self-evident. Usually two meters high and 12 to 14 strands is sufficient for most security situations. Of course, higher is better, but there is a diminishing security return for an electric fence much over two meters high.
2. The bottom strand is almost always a “hot” strand, and then alternating with grounded (good solid earth ground) strands. In a security fence you do not parallel the hot strands, but interconnect at the ends of the fence so that, electrically, there is only one strand that is doubled back on itself, and redoubled again if necessary. This type of connection allows a fence monitor to keep track of the condition of all of the fenced perimeter.
When working with the “human” pest, it is best to make the fence look as lethal as possible. 90% of the effectiveness is in the perception of the intruder or trespasser. Many sites selling electric fence components have a gallery of pictures that provide design ideas. Signs every 30′ (10 meters) are a good touch.
3. The biggest design difference is this: By looping connections and maintaining a single strand (electrically), you feed the high voltage into one end and monitor the high voltage at the far end of the strand. This ensures the high voltage is present all the time, throughout the complete fence.
If the high voltage is cut or shorted anywhere around the perimeter, then the High Voltage Monitor will close a set of contacts to activate an alarm.
The sophisticated Fence Hawk Plus monitor that we provide at Intelligent Fencing Systems will also provide an alarm when the voltage drops due to weeds, grass, or other undergrowth to maintain the maximum security.
Now the intruder cannot go over, under, or through the fence without being shocked, and the intruder cannot short out the fence or cut the wires without setting off the alarm.
This makes your fence virtually impossible to penetrate without a helicopter, crane or swinging vine.
However, remember that there is no device that is 100% secure. Watching any James Bond movie will show you that. The high voltage perimeter security array will keep out 99.99% of the intruders, but there is always a way to beat the device.
In high security installations the security is done in layers. If the first layer is penetrated, then the second, third, or the fourth layer or device will catch them. In these cases the electric array is usually the first or second layer of security.
A high voltage electric fence, properly designed and installed, is the most cost-effective high security method available today. Truly “State-of-the-Art.”
We designed this high security hybrid chain link / electric fence “turnkey” for perimeter defense with Fence Hawk Plus, as a counter-terrorist system for a major international corporation, but the design is basically the same for any high-security application. The status of each fence section, gate and all openings are all monitored and displayed on the command computer. If any fence section or gate is violated, it is instantly displayed on the central computer and turns on the monitoring camera for that section, including lighting when required. Click on photo for detailed 2 MB blowup. Fence Hawks are the key to making this an impenetrable barrier.
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