BACKGROUND TO THE INVENTION The theft of underground cables, usually those made of electrically conductive metals that can be sold as scrap and easily recycled, is a widespread problem which costs the relevant authorities and insurance companies considerable amounts of money annually. Inevitably, this loss is ultimately financed by the consumer.

This is only a small part of the consequences of an instance of the theft of an underground cable or, for that matter, any other cable. The further consequences are those of the interruption of the relevant services to the consumers that may be the private individual or, generally more seriously, business and industry, as the relevant service is frequently an electrical power supply or telecommunications service. The relevant business or industry is frequently seriously prejudiced by an occasion of cable theft in that business and the business generally cannot be carried on effectively until the relevant cable has been replaced. This may take of the order of days or even weeks in the case of serious occurrences.

Underground cables are typically stolen by attaching one end of the cable to a traction device such as to the tow-bar of a sufficiently powerful vehicle and pulling on the underground cable either in an axial direction until such time as the cables snaps at one point or another or becomes detached at its opposite end, or by driving the traction vehicle back along the path of the cable so as to rip it transversely upwards and back over itself. Frequently such thefts are carried out on newly laid cables or cables that have been partially laid and of which an end is easily accessible.

OBJECT OF THE INVENTION It is an object of this invention to provide a method and means that, in particular, assumes the form of an obstructive element for association with a cable, whereby the theft of underground cables in the manner outlined above may be successfully combated or at least the amount of cable stolen in any one attempt may be effectively limited.

SUMMARY OF THE INVENTION In accordance with one aspect of this invention there is provided a method of combating the theft of an underground cable comprising securing to the outside surface of a cable, at spaced intervals along the length thereof and prior to burying of the cable in an underground situation, a series of obstructive elements each of which engages the outer surface of the cable frictionally, or physically, or both, so that axial movement of cable relative to the obstructive element is substantially inhibited, and wherein the outer peripheral dimensions of the obstructive element are substantially greater than the diameter of the associated cable such that the obstructive element presents a relatively substantial resistance to movement of the cable in the axial direction in a buried condition thereof.

A further feature of this aspect of the invention provides for the obstructive elements to be configured to additionally inhibit the forcible removal of a buried cable by pulling it back over itself.

The invention also provides an underground cable having a series of axially spaced obstructive elements secured to the outer surface thereof in the manner indicated above. Preferably, the obstructive elements are arranged in pairs whereof the two elements of a pair are spaced relatively closely together compared to the spacing between adjacent pairs.

In accordance with a second aspect of the invention there is provided an obstructive element of generally planar construction and having an aperture passing through it with the axis of the aperture being at generally right angles to the plane of the planar element, and clamping means for engaging the outer surface of a cable passing through said aperture to lock the obstructive element relative to the cable in the axial direction thereof with the obstructive element extending in a generally radial direction relative to the cable.

In one form, the obstructive element comprises two parts together operatively defining the aperture through the obstructive element and wherein the two parts each define a part of the periphery of said aperture, the two parts having cooperating formations enabling them to be locked in operative engagement with the outer surface of a cable with the cable located in said aperture.

Further features of this form of the invention provide for the formations to be such that the two parts are inter-engaged by relative movement thereof in a generally diametrical direction ; for the obstructive element to be of substantially plate like configuration with the two parts thereof being substantially coplanar and each preferably defining a roughly semicircular recess in its periphery so that the two recesses together define a generally

substantially circular aperture conforming to a circular cross-sectioned cable ; for the periphery of the aperture to have a series of biting formations for biting into the outer surface of a cable to form a physical attachment thereto; and for the cooperating formations to either include two protruding tongues of which one is located at each side of the recess defined by that part of the obstructive element and wherein each tongue has one or more detent formations thereon cooperating with catch formations associated with cooperating socket for receiving the tongue or, alternatively, for the two parts to be hinged together at one side in which case only one such tongue and cooperant catch formation is required on the side of the aperture opposite the hinge.

Still further features of the second aspect of the invention provide for the obstructive element to have a foot, usually integral with one part of the obstructive element, the foot preferably extending in a plane parallel to the axis of the aperture through the obstructive element ; for the two parts of the obstructive element to be made from a suitable injection moulded plastics material optionally carrying hardened inserts as and where required; and for the obstructive element to be provided with a generally diametrically extending formation about which the obstructive element can bend, fold or hinge in which case diametrically opposite cable severing formations may be carried by the obstructive element so that the severing formations move towards each other as the obstructive element bends or hinges about said diametrically extending formation. The effect of the latter is that the severing formations tend to engage a cable, upon relative axial movement thereof, in a manner calculated to promote fracturing of the cable.

In a second form, an obstructive element may be a simple metal plate having an aperture therethrough and a slit extending radially through the metal plate from the aperture to the periphery of the plate. In such a case the metal plate can be deformed by moving the two edges of the slit away from each other in

order to bend the plate to a roughly helical shape to receive the thickness of a cable between such ends and after installation of the cable in the aperture the two edges of the slit can be moved back into roughly coplanar relationship whilst simultaneously biting into the outer surface of the cable to lock it in position.

In a third form of the invention the obstructive element can be of planar construction and have a fixed aperture therethrough that does not open so that the obstructive element must be threaded onto the free end of a cable as it is one-off its cable drum during the laying process. In this case it is preferred that the aperture be oversized relative to the outer diameter of a cable on which it is to be used in which case a cooperating clamping member that can be introduced diametrically over a cable cooperates with the aperture to clamp the obstructive element relative to the cable.

This third form of the invention has the advantage that a single obstructive element can be used on different sized cables with the clamping member being varied according to be size of the cable. Such a damping member can be injection moulded in different sizes. The clamping member may have an outer surface of slightly oval shape to cooperate with a complementarily oval aperture through the obstructive element so that when they are rotated relative to each other a radially inwardly directed clamping force is applied to the clamping member to cause it to contract and radially engage the outer surface of a cable. The clamping member in such an application is preferably of a generally tubular form having a circumferential gap in the periphery thereof for enabling the effective diameter of the clamping member to be decreased to cause it to radially engage the outer surface of a cable, in use.

In a fourth form of obstructive element according to the invention, a pair of axially spaced obstructive elements are interconnected by means of

circumferentially spaced ties serving to fix them axially relative to each other and to create a space between the obstructive elements and ties that becomes filled with ground or other material in which a cable is buried. This arrangement is particularly effective in inhibiting a sideways movement of a cable such as would result from an attempt to pull a cable back over itself in a manner indicated above. In a practical arrangement, it is therefore preferred that a composite obstructive element as described above be employed, at least one on each side of a joint in a cable and one towards each end of the cable.

In order that the above and other features of the invention may be more fully understood different embodiments thereof will now be described with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS In the drawings:- Figure 1 is an elevation illustrating a cable fitted with a series of one form of obstructive element according to the invention; Figure 2 is an isometric view of one embodiment of the obstructive element according to the invention; Figure 3 is a front elevation thereof illustrating biting formations associated with the aperture through the element ; Figure 4 is an exploded view illustrating the two parts of the obstructive element illustrated in Figures 2 and 3;

Figure 5 is a schematic sectional elevation taken through an alternative embodiment of obstructive element ; Figure 6 illustrates in similar elevation the operation of the embodiment illustrated in Figure 5; Figure 7 is an elevation of a further and particularly simple embodiment of the invention; Figure 8 is an elevation of a further embodiment of the invention employing a separate clamping member; Figure 9 is an enlarged detail of the clamping member illustrated in Figure 8 and showing the cooperation thereof with the aperture through the obstructive element ; Figure 10 is an isometric view of a composite obstructive element according to the invention; Figure 11 is a schematic plan view and showing one arrangement of obstructive element along the length of a cable ; Figure 12 is a view similar to Figure 11 the illustrating a preferred arrangement at a cable joint; Figure 13 is an isometric view of a single fabricated variety of obstructive element ; and, Figure 14 is a side view of a composite obstructive element embodying the element illustrated in Figure 13.

DETAILED DESCRIPTION WITH REFERENCE TO THE DRAWINGS Referring firstly to Figure 1 of the drawings, the basic concept of the invention is illustrated which involves the securing of a series of obstructive elements (1) to an underground cable (2) so that each of the obstructive elements present a relatively substantial face (3) directed in each of the two opposite axial directions in which the cable extends. The obstructive elements engage the outer surface of the cable, optionally fractionally, but preferably by physically deforming the surface to form a physical engagement. It will be understood that the elements will significantly limit the extent to which the cable can be pulled out of the ground (indicated by numeral (4)) in the axial direction of the cable.

The exact nature of the obstructive elements can be varied widely and the following embodiments thereof are given simply for the purpose of illustration.

Referring now to the obstructive elements illustrated in Figures 2 to 4, each element is made in two parts (5) and (6) which clip together in the general diametrical direction, in order to install the obstructive element on a length of cable. In this case each of the two parts is of plate-like configuration and each defines in its periphery a substantially semicircular recess (7) so that the two recesses together form the final aperture (8) through which the cable will extend, in use.

The one part (5) has a pair of parallel integral tongues (9) one of which is located on each side of the semicircular recess (7). Each of these tongues has a series of detent formations (10) extending along the length thereof and which cooperate with catch formations in sockets (not shown) configured to receive the tongues in well-known non-releasable manner.

The edge of each of the two semicircular recesses has a series of biting formations (11) in the form of teeth for physically engaging and deforming, at least to some extent, the outer surface of the cable so as to become substantially immovable relative to the cable in an axial direction after installation.

The two parts may be made of injection moulded plastics material having suitable strength characteristics or they may be made of die-cast, forged, or other suitably formed metal.

Clearly, one particular shape and configuration of this form of obstructive element will be provided for each different diameter of cable although it is also within the scope of this invention that inserts could be produced for lining the recesses so as to define smaller diameter apertures should this be required.

In any event, in order to install the obstructive element described above onto a cable the one part is located on one side of the cable and the other is moved inwardly in a diametrical direction so that the tongues engage in the sockets and the two parts become clamped together in coplanar relationship with the cable passing through the aperture. The size of the aperture is such that the two parts will be forced together to effect the physical engagement indicated above. A special lever based tool could be provided for the purpose. Alternatively the two parts could be urged together by means of the percussive blows of a hammer or the like.

As an additional security feature of this embodiment of the invention, the one part (6) is provided with a foot (12) in the form of a plate extending at right angles to the part and at its outermost extremity relative to the recess (7).

This foot can be used to support the cable assembly during installation. It also serves to inhibit the cable from being pulled out sideways as would be

occasioned by an attempt to pull the cable back over itself in the manner indicated above.

The foot serves a still additional purpose in the event that the cable is pulled axially in that it will urge the obstructive element to rotate about the foot. This will have the effect of causing the diametrically opposite edges of the aperture to more firmly engage the cable and, indeed, will tend to bend the cable out of its straight condition. In consequence a kink will develop in the cable and this will make it even more difficult for the cable to be pulled through the ground. Indeed by configuring the aperture appropriately this tendency of the obstructive unit to rotate may be designed to cause injury to the cable to an extent that it tends to break at that point. The effect of this is to limit the amount of cable stolen in that the cable tends to break rather close to the point at which traction is being applied to it.

Also, it is preferred that the foot be close to the aperture, as illustrated in order to prevent possible damage to the cable during the process of burying it should it be supported on sharp edges presented by the lower periphery of the aperture.

In another embodiment of the invention illustrated in Figures 5 and 6 the obstructive element may be formed with special severing formations (13) projecting outwardly therefrom in an axial direction and a diametrical formation (14) about which the obstructive element can bend or hinge. The severing formations each have a sharpened edge (15) that may be defined by a hardened insert adapted to cause injury to the cable so as to induce the cable to break at that point. As shown clearly in Figure 6, as an attempt is made to pull the cable (16) axially through the ground, the resistance of the ground tends to cause the obstructive element to bend about the diametrical formation (14) and in consequence the sharp edges (15) to move closer together and deform the cable with a result indicated above.

Figure 7 illustrates a simple embodiment of the invention in which a metal plate (17) is provided with an aperture (18) of the appropriate size for the purpose indicated above and a radial slit (19). The metal plate can be deformed to a roughly helical configuration by parting the two edges of the slit in the direction of the axis of the aperture so that a gap is created which can receive the cable in a direction at generally right angles to the axis of the aperture. After introduction of the cable into the aperture the plate can be deformed so that the two edges of the slit (19) are once more roughly coplanar.

Turning now to the embodiment of the invention illustrated in Figures 8 and 9, in a third form of the invention, the obstructive element assumes the form of a flat disc (20) having an oversized aperture (21) therethrough. Of course, the outer peripheral shape of the obstructive element is irrelevant and it could be of any convenient shape, in particular square, as production of square plates may be most practical.

In this case the aperture cooperates with a clamping member (22) having a gap (23) in its periphery to enable it to be clipped over a central cable (24) and to thereafter be engaged by the aperture (21) to cause the clamping member to firmly clamp and lock the assembly onto the cable. Conveniently this is achieved by making the aperture and the outer periphery of the clamping member slightly oval as illustrated clearly in Figure 9 so that when the one is rotated relative to the other a radial clamping force is exerted on the clamping member. This radial clamping force causes the clamping member to firmly engage the cable and to become axially locked relative thereto. Of course, the clamping member could easily be made in two parts to permit easy installation thereof.

Figure 10 illustrates a fourth form of the invention in which a pair of axially spaced obstructive members (25) are connected by a series of longitudinally

extending ties (26) so that a composite obstructive member generally indicated by numeral (27) is formed. The composite obstructive member assumes the general form of a sort of cage that will allow soil or other aggregate in which a cable is buried to enter the space between the ties so that an effective composite anchor is formed. This substantially prevents a cable fitted with the composite obstructive member from being pulled sideways from the earth as would be the case if a cable is pulled back upon itself.

Figure 11 illustrates one preferred installation according to the invention wherein a cable (28) is fitted with pairs of obstructive members (29) of any of the types described above (other than the composite obstructive member (27)) wherein the members of a pair are spaced relatively close together and the pairs are spaced relatively far part. It has been found that this arrangement operates particularly successfully.

Figure 12 illustrates a preferred installation in instances in which a joint (30) in a length of cable is provided. In this case a composite obstructive member (27) is installed on each side of the joint and pairs (29) of other obstructive members at other spaced locations relative to the composite obstructive members. The composite obstructive members are also preferably installed towards each end of a cable.

It to be understood that numerous other embodiments of the invention a possible within the scope hereof.

Simply by way of example, the obstructive element can be fabricated as illustrated in Figure 13 in which case two identical plates (31) each of which has a substantially semicircular recess (32) in its one edge can be provided with prefabricated brackets (33) bolted thereto whereby they can be secured together in coplanar manner with a cable tightly surrounded by the aperture

formed by the two semicircular recesses. As illustrated in Figure 14 two of these fabricated obstructive elements and generally indicated by numeral (34) can be employed using screw threaded rods (35) an cooperating nuts (36) to interconnect the four corners of two longitudinally spaced fabricated obstructive elements to form a fabricated composite obstructive element of the general type described with reference to Figure 10.

It will be understood that numerous other variations are possible within the scope of the invention.