AU2003214410A1 - Improvements relating to electrical link boxes - Google Patents

Description

WO 03/081727 PCT/GB03/01095 IMPROVEMENTS RELATING TO ELECTRICAL LINK BOXES This invention relates to a so-called "link box", that is to say to a unit intended for installation in an electrical supply cable or cables so as to permit temporary 5 interruption of current flow along that cable or cables. In particular, the invention relates to link boxes of the "untailed" type which are filled, in use, with an insulating resin. Link boxes are widely used where it is desired temporarily to interrupt the supply of 10 electric current in a cable or cables, typically a three-phase AC mains supply. Such boxes are commonly installed in underground chambers in roadways or other paved areas. In the simplest case, the link box is interposed between two parts of a cable and serves to either permit or interrupt the flow of current along the cable. In such a case, the link box contains two sets of terminals, for the 15 individual cores of the two parts of the cable, and a set of mechanical links are used to connect the corresponding terminals to complete the current path. Physical removal of the link interrupts the flow of current. The links themselves are accommodated within a link housing within the link box, connecting members extending through the walls of the link housing and being connected to the 20 terminals externally of the link housing. Some link boxes are supplied as pre-assembled units complete with cable "tails" that are then connected to underground cables externally of the link box. Other link boxes are referred to as "untailed", the underground cables being connected 25 directly to the terminals in the link box. In the installation of such an "untailed" link box, after the cables have been connected, it is customary for the terminals to be encapsulated in an insulating material, commonly referred to as "potting resin" which cures within the link box and insulates the terminals from the environment and from each other. 30 It has now been found that problems may be encountered with such link boxes. In particular, it has been found that cracks may occur at the interface between the WO 03/081727 PCT/GB03/01095 2 potting resin and the link housing. This interface is often cracked or moved after the setting of the potting resin and this can allow the ingress of moisture at the interface. Leak paths are therefore formed between the phases of the electricity cable, which is highly undesirable. 5 There has now been devised a link box which overcomes or substantially mitigates the above-mentioned or other disadvantages of the prior art. According to the present invention, there is provided a link box for connecting 10 electricity cables, the link box comprising an inner enclosure, an outer enclosure defining one or more cable-receiving spaces between the inner enclosure and the outer enclosure, and at least one pair of connecting members extending from the interior of the inner enclosure into the cable-receiving spaces such that connection of the connecting members within the inner enclosure establishes electrical 15 connection between electrical cables connected, in use, to the connecting members in the cable-receiving spaces, wherein the exterior of the inner enclosure is configured to interlock with insulating material introduced, in use, into the cable-receiving spaces. 20 The link box according to the present invention is advantageous primarily because the external configuration of the inner enclosure causes the inner enclosure and the insulating material ("potting resin") to interlock, thereby reducing the likelihood of the interface between the resin and the inner enclosure being moved or cracked, which would allow ingress of moisture and the formation of leak paths. 25 The exterior of the inner enclosure is preferably formed with projections and/or recesses to provide for interlocking engagement of the inner enclosure with the insulating material. Such formations are preferably interposed between adjacent connecting members, thereby increasing the tracking path between each phase of 30 the cables.

WO 03/081727 PCT/GB03/01095 3 As is conventional, the inner enclosure is preferably vacuum-formed from plastics material and the formations are preferably integrally formed with the inner enclosure. The formations are preferably projections which extend outwardly from the inner enclosure. The projections are preferably tapered in such a way so as to 5 facilitate the vacuum-forming of the inner enclosure. The projections most preferably include locking grooves or undercuts which provide the locking mechanism between the external surface of the inner enclosure and the resin. Most preferably, the formations are projections of dovetail section, thereby 10 providing two locking grooves, one at each side of the projection, and are tapered so as to allow the integral vacuum-forming of the inner enclosure and the projections. The invention will now be described in greater detail, by way of illustration only, 15 with reference to the accompanying drawings, in which Figure 1 is a plan view of a link box according to the present invention, in use; Figure 2 is a sectional view of the link box on the line 11-11 of Figure 1; 20 Figure 3 is a front elevation of a central turret forming part of the link box; Figure 4 is a plan view of the central turret within the link box; and 25 Figure 5 is a section on the line V-V in Figure 3. A link box according to the invention is shown in Figures 1 and 2 and is generally designated 10. The link box 10 comprises an outer container 20 with a container lid 22 and a central turret 30 with a removable turret lid 32. The container 22, 30 central turret 32 and lids 22,32 are typically vacuum-formed from plastics material, preferably polyurethane. The link box 10 further comprises three pairs of connectors 42 which extend through opposite walls of the turret 30. Removable WO 03/081727 PCT/GB03/01095 4 links 44 can be fitted between the connectors 42 within the turret 30 so as to establish electrical connection between them. Clamps 40 are fitted to the ends of the connectors 42 that are external to the turret 30 and serve for connection of the connectors 42 to the corresponding phase conductors 18 of two cables 14,15. 5 The clamps 40, connectors 42 and links 44 are therefore formed in a material with an excellent electrical conductivity, such as copper. The outer container 20 and the container lid 22 together form an enclosure with a circular opening at each end thereof. A cable 14,15 passes through each of the 10 circular openings with a close fit and into the link box 10. The container lid 22 includes a square opening through which the turret 30 projects, as described more fully below. The turret 30 is of box shape with an open upper surface and includes three 15 internal enclosures 34 separated by vertical partitions. The exterior walls of the turret 30 are formed with a shoulder or ledge 33 from which the upper portion tapers inwardly. The turret lid 32 is configured so as to engage the exterior of the upper portion with a close fit and to rest upon the shoulder 33. The entire perimeter of the lowermost edge of the turret 30 has an outwardly extending 20 horizontal flange 36. The turret 30 is located within the enclosure formed by the outer container 20 and the container lid 22, extending through the square opening of the container lid 22 with a close fit. The turret 30 is dimensioned such that the upper portion of the turret 30 and the shoulder 33 are located externally of the enclosure, thereby allowing removal of turret lid 32 without having first to remove 25 the container lid 22. The turret 30 further includes a lateral extension 38 of reduced dimensions, as shown in Figures 3 and 4. Each cable 14,15 separates within the link box into three cores 16 which each contain a phase conductor 18. Each conductor 18 of cable 14 is held by a 30 separate clamp 40 mounted externally of the turret 30. Each clamp 40 is fixed to a connector 42 which passes through the wall of the turret 30 and into one of the enclosures 34. The conductors 18 of cable 15 are fixed to similarly arranged WO 03/081727 PCT/GB03/01095 5 clamps 40 and connectors 42 at the opposite face of the turret 30 such that each pair of corresponding connectors 42 extend into an enclosure 34 of the turret 30 and are joined by a link 44. Each link 44 is therefore isolated from the other links 44. A further connector 42 passes through the extension 38, thereby providing an 5 additional connection means without a link 44. In use, with the turret 30 in position within the container 20, each conductor 18 is fastened in a clamp 40 and the container lid 22 is positioned on the outer container 22. Potting resin 50 is then introduced into the link box 10 through an inlet (not 10 shown) until the potting resin 50 encapsulates the cables 14,15, cores 16, conductors 18, clamps 40 and connectors 42 which are situated within the link box 10 and external of the turret 30. The potting resin 50 is then allowed to set. The potting resin 50 is typically of the same material as the outer container 20, turret 30 and lids 22,32, preferably polyurethane. As shown in Figure 2, the potting resin 15 50 completely fills the enclosure formed by the outer container 20 and the container lid 22. The link box 10 as hereinbefore described is entirely conventional and well known in the art. However, the link box 10 according to the present invention further 20 includes projections 60 on the external faces of the turret 30. Turning now to Figures 3 and 4, the projections 60 are integrally formed with the turret 30, typically using vacuum-forming. A projection 60 is interposed between each connector 42 on the lower portion of the turret 30. In frontal view, as shown 25 in Figure 3, the projections 60 are trapezoidal in shape with the upper and lower edges being parallel and the sides being tapered, thereby facilitating the vacuum forming process. The projections 60 extend upwardly from the flange 36 to a position which is below the shoulder 33. In plan view, as shown in Figures 4 and 5, and by the broken lines indicating hidden detail in Figure 3, the projections 30 60 are dove-tail in shape such that grooves 62 are formed on either side of each projection 60.

WO 03/081727 PCT/GB03/01095 6 In use, potting resin 50 is introduced into the enclosure formed by the outer container 20 and container lid 22 as described above. The potting resin 50 flows around the projections 60 and into the grooves 62. Once the potting resin 50 is set, the configuration of the projections 60 and the grooves 62 interlocks the 5 external surface of the turret 30 and the potting resin 50. The likelihood of the interface between the potting resin 50 and the external face of the turret 30 being cracked or moved by subsequent movement of the link box 10 is therefore greatly reduced.

Claims (8)

1. A link box for connecting electricity cables, the link box comprising an inner enclosure, an outer enclosure defining one or more cable-receiving spaces 5 between the inner enclosure and the outer enclosure, and at least one pair of connecting members extending from the interior of the inner enclosure into the cable-receiving spaces such that connection of the connecting members within the inner enclosure establishes electrical connection between electrical cables connected, in use, to the connecting members in the cable-receiving spaces, 10 wherein the exterior of the inner enclosure is configured to interlock with insulating material introduced, in use, into the cable-receiving spaces.

2. A link box according to Claim 1, wherein the inner enclosure has formations such as projections and/or recesses to provide for locking engagement of the inner 15 enclosure with the insulating material.

3. A link box according to Claim 2, wherein the formations are interposed between adjacent connecting members. 20

4. A link box according to Claim 2 or Claim 3, wherein the formations are integrally formed with the inner enclosure.

5. A link box according to any one of Claims 2 to 4, wherein the formations are projections. 25

6. A link box according to Claim 5, wherein the projections are tapered in such a way so as to facilitate vacuum-forming of the inner enclosure.

7. A link box according to Claim 5 or Claim 6, wherein the projections include 30 locking grooves or undercuts. WO 03/081727 PCT/GB03/01095 8

8. A link box according to Claim 7, wherein the projections are of dovetail section.