GB2119550A - Electrified fence - Google Patents

Abstract

An electrified fence in which an alarm operates when any part of the fence is cut comprises three fence strands 1, 2 and 3, fence strands 1 and 2 having first current carrying conductors 4 and 5 which are arranged to form a mesh and second current carrying conductors 6 and 7 which are interlinked with the mesh and face strand 3 including two current carrying conductors 8 and 9. All the strands 1, 2, 3 are connected via a junction box 17, housed within end post 12, and a control cable 18 to a control panel (not shown) which emits an audible and/or visual warning when any part of the fence is cut. Fence strand 3 also incorporates an alarm 22 which emits an audible and/or visual warning when a gate (not shown) built into the fence is unlocked and/or opened. The horizontal tensioned conductors 6, 7, 8 and 9 serve to make it difficult for an intruder to enter the prohibited area bounded by the fence even if part of the fence is cut after short-circuiting the relevant sections thereof. <IMAGE>

Description

SPECIFICATION An electrified fence The present invention relates to an electrified fence of the type in which an alarm operates when any part of the fence is cut, by say, a potential intruder.

According to the present invention, there is provided an electrified fence of the type in which an alarm operates when any part of the fence is cut, the fence including a first current carrying conductor arranged to form a mesh and a second current carrying conductor held between two points at each end of the fence and interlinked with the mesh.

The first and second current carrying conductors may form part of the same fence strand.

Preferably the fence includes at least two fence strands having first and second current carrying conductors, the respective first conductors of each strand being arranged to form the mesh and the respective second conductors of each strand being held between two points at each end of the fence and interlinked with the mesh.

Suitably the second conductors are spaced from each other.

Conveniently the or each second conductor is held in tension between the two points.

Preferably the or each second conductor extends substantially horizontally along the fence.

In a preferred embodiment of the invention, the fence includes a further strand arranged so as to provide two current carrying conductors which are held between points at each end of the fence and are interlinked with the mesh.

Preferably the conductors in the further strand are spaced from each other.

Suitably the conductors in the further strand are spaced from the or each second conductor.

Conveniently the conductors in the further strand are held in tension between the points.

Preferably the conductors in the further strand extend substantially horizontally along the fence.

The further strand may be connected to an alarm which operates when a gate is unlocked and/or opened.

Preferably the mesh comprises vertically extending portions which are arranged so that each portion is of opposite polarity to its neighbouring portion.

An embodiment of the invention will now be particularly described with reference to the accompanying drawings in which: Figure 1 shows a section of the fence and Figure 2 is a schematic view of the fence showing in detail one end thereof.

Referring to the drawings and particularly Figure 2, the fence comprises three fence strands 1, 2, and 3 which comprise lengths of an electrically conducting wire coated with identical insulating material (such as plastics) so that, on visual inspection, the strands cannot be separately identified.

Two of the strands 1, 2, comprise first current carrying conductors 4 and 5 which are interlinked with themselves and with each other in such a manner as to form a mesh network. The strands 1, 2, also comprise second current carrying conductors 6 and 7 which are contiguous with their respective first conductors 4 and 5. These second conductors 6 and 7 extend horizontally across the fence, and vertically spaced from each other and are interlinked sequentially with the mesh netting in the manner of a weave, A further strand 3 comprises two current carrying conductors 8 and 9 which also extend horizontally across the fence, are vertically spaced from each other and from the conductors 6 and 7 and are also interlinked or woven with the mesh.

Located at one near end of the fence is a vertical steel stiffening plate 10 which forms a support for the end of the fence mesh. Welded to the stiffening plate 10 are four vertically spaced right angle steel brackets 11. A vertical hollow concrete post 12 is located adjacent to the stiffening plate 10 so as to abut one arm 13 of each bracket 11. Extending through each arm 13 and through the post 12 are four tension bolts 14 which are threaded to engage nuts 1 5 adjacent the far side of the post 12. Each bolt 14 is provided with an eye 1 6 for connection to a suitably looped end of each of the conductors 6, 7, 8 and 9. The other end of the conductors 6, 7, 8 and 9 at the far end of the fence (not shown) is clamped or suitably secured to another concrete post (not shown).Thus suitable rotation of the nuts 1 5 to cause the bolts 1 4 to move towards the post 12 also causes each of the conductors 6, 7, 8 and 9 to be tensioned between the near post 12 and the far post (not shown). As shown schematically in Figure 2, the second conductors 6 and 7 are looped back on themselves at the far end of the fence so as to form the respective contiguous first conductors 4 and 5 which are suitably interlinked to form the mesh.

Each end of the strands 1, 2, and 3 leads into the hollow post 12 and extends vertically downwards into a metal clad junction box 1 7 which is located within the post 12. Extending vertically downward from the junction box 1 7 is a suitable power cable 1 8 which after leaving the post 12 runs underground to a control panel (not shown). Each of the horizontal conductors 6, 7, 8 and 9 is formed with a branch 19 close to its adjacent tension bolt 14 for connecting that end of the conductor via the post 12 to the junction box 17.

The polarity of adjacent linked vertical sections of the fence strand conductors 4 and 5 are reversed to prevent the adjacent sections being shorted out by an intruder. In this case, therefore, one section is live while an adjacent section is neutral. Thus the polarity of section 4a is opposite to that of 4b while the polarity of section 5a is opposite to that of section 4b and section 5b.

Similarly the polarity of section 5b is opposite to that of both section 4c and 5a and so on along the fence.

To further prevent shorting out of the conductors by intruders, the base of the mesh is buried in a concrete skirt 20. As an additional precaution before the base of the mesh is buried an additional non-current carrying tension wire 21 may be interwoven with the mesh and secured to the end posts before being buried with the mesh base. The wire 21 may be used as a current carrying conductor as well should this be desired.

While not shown, each of the strands 1, 2 and 3 is connected via the junction box 1 7 and power cable 1 8 to a control panel. The panel may incorporate any suitable and readily available alarm circuitry such that when any part of the fence is cut, an alarm operates at the control panel warning of the unauthorised intrusion. The alarm may be either an audible or visual alarm or both.

The strand 3 may additionally be connected to a further alarm 22 also incorporated into the control panel for issuing an audible and/or visual warning when intruders unlock and/or open a suitable gate built into the electrified fence. Such an alarm 22 may incorporate suitable and readily available time delay circuitry to enable authorised personnel to re-lock and/or close the gate within the delay period and without operating the alarm.

Referring to Figure 1, the fence may be secured as conventional to suitable concrete or steel support post 23 disposed at intervals along the fence perimeter, provided that the conductors 6, 7, 8 and 9 can move relative to the posts 23 to enable the conductors to be suitably tensioned.

A barbed wire barrier 24 can also be secured along the tops of the posts 23 in the conventional manner for additional security.

With the fence arrangement shown in the drawings and described in detail above, it becomes very difficuit for an intruder to gain entry to an area fenced off or enclosed by the fence by cutting the fence. Should an intruder actually succeed in shorting out a section of the fence mesh and then should he cut the relevant mesh section, the horizontal wires, if left in position, still make entry difficult since they tend to hold the fence together even when out. If the intruder tries to overcome this problem by attempting to short out the horizontal wires as well he may break the shorted out circuit when the horizontal wires are cut since as these are under tension the separate sections will tend to spring apart in an unpredictable manner.

Claims (14)

Claims

1. An electrified fence of the type in which an alarm operates when any part of the fence is cut, the fence including a first current carrying conductor arranged to form a mesh and a second current carrying conductor held between two points at each end of the fence and interlinked with the mesh.

2. A fence as claimed in Claim 1 in which the first and second current carrying conductors form part of the same fence strand.

3. A fence as claimed in Claim 2 in which the fence includes at least two fence strands having first and second current carrying conductors, the respective first conductors of each strand being arranged to form the mesh and the respective second conductors of each strand being held between two points at each end of the fence and interlinked with the mesh.

4. A fence as claimed in Claim 3 in which the second conductors are spaced from each other.

5. A fence as claimed in any preceding claim in which the or each second conductor is held in tension between the two points.

6. A fence as claimed in any preceding claim in which the or each second conductor extends substantially horizontally along the fence.

7. A fence as claimed in any of the preceding claims in which the fence includes a further strand arranged so as to provide two current carrying conductors which are held between points at each end of the fence and are interlinked with the mesh.

8. A fence as claimed in Claim 7 in which the conductors in the further strand are spaced from each other.

9. A fence as claimed in Claim 7 or Claim 8 in which the conductors in the further strand are spaced from the or each second conductor.

10. A fence as claimed in any of claims 7 to 9 in which the conductors in the further strand are held in tension between the points.

11. A fence as claimed in any of claims 7 to 10 in which the conductors in the further strand extend substantially horizontally along the fence.

12. A fence as claimed in any of claims 7 to 11 in which the further strand is connected to an alarm which operates when a gate is unlocked and/or opened.

13. A fence as claimed in any of the preceding claims in which the mesh comprises vertically extending portions which are arranged so that each portion is of opposite polarity to its neighbouring portion.

14. An electrified fence substantially as hereinbefore described with reference to the accompanying drawings.