GB2232828A - Connection providing earth continuity for junction box - Google Patents

Abstract

An earthing connection particularly for earth continuity of cables received in non-metallic junction boxes, comprising an apertured body (10, 12) which fits around a part to be earthed (24), for example a cable gland, and means (18, 20, 22) for tightening the apertured body onto the part to be earthed. Teeth (40) may improve the connection. Other connections (figs. 3 to 5) having different configurations are disclosed. A series of connections connected by links (30, 36) provide for earth continuity. <IMAGE>

Description

EARTH CONTINUITY Traditionally, electrical equipment such as terminal boxes and junction boxes were made of metal and problems about electrical continuity did not arise. With the replacement of metal equipment by equipment made of plastics it is now important to ensure that there is proper earth continuity between the conductors or other components i.e. cable glands for armoured cable that are led into the equipment.

The regulations provide that earthing in such equipment is not permitted by trapping an earth plate against the inner wall of the equipment, which being non-metallic is considered to be capable of relaxation thus giving an unstable connection.

Attempts have been made to obtain an earth connection on that part of a component, for example the threaded entry of a cable gland, that projects into the equipment, by trapping an earth plate between lock nuts engaged on the said entry portion. However, it is often the case that there is not sufficient entry portion projecting into the equipment, particularly when a seal is provided between the outer wall of the equipment and the cable gland. In addition because of the limited space within the equipment it is difficult to get a spanner onto the lock nuts to tighten them so that frequently they are left loose. Checks on equipment often reveal earthing faults due largely to these problems.

The present invention seeks to provide a simple means of providing earth continuity which overcomes the above-mentioned problems.

Acording to the invention there is provided an earthing connector comprising an apertured body adapted to fit around a part to be earthed projecting through the wall of electrical equipment and means for reducing the area defined within the apertured body for tightening the body onto said projecting part.

In a preferred embodiment of the invention the body comprises a split annulus. The means for reducing the area defined within the annulus comprises a connector for drawing the adjacent edges of the split towards each other. If desired the connector may also provide a terminal for an earth connection.

The invention also provides an assembly comprising a housing, an electrically conductive member extending through the housing, and an earthing connector as defined above fixed to the part of the member that projects into the housing.

The housing of the assembly may be non-conductive, at least in part, and the member to be earthed may extend through a non-conductive part of the housing.

Specific embodiments of the invention will now be described by way of example with reference to the accompanying drawings in which: Fig.l is a perspective view of an apertured body; Fig.2 is a part section through a terminal box; Figs.3 and 4 are different embodiments of apertured bodies.

Referring to Fig.l an apertured body comprises a split ring 10, 12 having out-turned tabs 14 at each free end. Apertures 16 are provided in the tabs 14 for receiving the bolt 18 of a saddle clamp 20. The clamp is completed by a nut 22 preferably of square external profile as illustrated. Although not illustrated in Fig.l an assembly of bolt 18, saddle clamp 20 and nut 22 is provided for each pair of adjacent tabs 14.

The apertured member can be clamped around the threaded end 24 of the entry portion of a cable gland 26 that projects into a terminal box 28, as shown in Fig.2 by tightening the bolts 18. This is preferably effected by using a screw driver, no other tool being needed because the square shaped nut 22 engages against the face of the split ring half 12 and cannot rotate.

This assembly does not, therefore, require the use of a spanner and hence the limited space inside the terminal box does not prevent the apertured member from being properly tightened. In addition the apertured body only requires a very short length of cable entry portion to be available, generally about one thread pitch, far less than is necessary to lock an earth connection onto the entry portion by means of lock nuts. As can be seen in Fig.2 the apertured member does not require to be clamped against the inner wall of the terminal box and so the regulation previously referred to is complied with.

The bolt 18 saddle clamp 20 and nut 22 provides a convenient location for attachment of a terminal for an earth connector 30. As illustrated in Fig.2 the entry portions of a plurality of cable glands can be linked together by earth connectors 30 and further earth connectors 32 led to an earthing terminal 34.

Where two entry portions are in close proximity as illustrated on the left of Fig.2 a strap 36 may extend between the pairs of tabs on each apertured body that are adjacent each other. Instead of linking the earthing connector to earth by a flexible connector it is within the scope of the invention to provide that the earthing connector makes direct contact with earth for example by means of bolt 18 threadedly engaging a threaded aperture in an earth plate or post fixed to an earth plate. By this arrangement the tightening of the earthing connector around end 24 also makes the earth connection in one operation thus eliminating the risk that the filter will forget to link the earthing connector to the earth terminal.

Teeth 40 may be provided on the inner annular edge of the apertured body which will bite into the cable gland or other item when the apertured member is tightened around it, thus improving the electrical continuity. If desired the inner edge of the apertured body may be tapered in cross-section so that it can be received in the trough of the thread form.

Depending upon the pitch of the thread, an apertured body that is so engaged may, when tightened around the thread be slightly skewed, that is to say one split ring may not be quite aligned with the other half and thus the tabs 14 on one split ring may not register with the tabs on the other split ring. To deal with that the tabs 14 or the bores therein which receive the bolts 18 can be offset to the extent necessary to bring them into alignment when the apertured body is engaged around a thread.

Other forms of apertured body can be used in place of the assembly described with reference to Fig.l.

For example, as shown in Fig.3, the apertured body can comprise a U-shaped rod 42. Open-sided housings 46 are fixed at their lower side to the U-shaped rod.

The housings which receive a saddle 44 through their open sides are provided in their upper surfaces with a tapped bore. Tightening of bolts 48 in the tapped bores urges the bolts into engagement with the saddle and in turn urge the saddle towards the base of the U-shaped rod thus clamping around a gland entry portion 24 or similar item. As shown in Fig.3 the assembly provides a very convenient way of securing an earth connector between the Another form of apertured body is shown in Fig.4.

Instead of being formed in two separable parts the apertured body comprises a split ring 50, 52 which is hinged together as at 54, tabs 14 being provided at the free ends. The hinge can also serve as a terminal for an earth connector. The hinge is offset so that the body will line up with the thread pitch. Instead of a split ring the apertured body may be unitary as illustrated in Fig.5 and weakened by a slot 56 at the side opposite to the tabs 14 to enable the body to be fitted around a gland entry or other item. Weakening can be provided in other locations and not necessarily at the site shown in Fig.5. In addition the weakening need not be effected by a slot and other cut out shapes may be adopted.

In some circumstances it may be desirable to form the inner edge of the apertured body so that it can be threadedly engaged with a threaded gland entry or similar threaded item. A seal can then be provided on one face of the apertured body which can be urged against the inner surface of the wall of a terminal box by tightening the apertured body onto the gland entry.

It will be evident from the foregoing that the invention provides a simple, but effective means of ensuring good earth continuity where there is limited space and also where there is only a limited area available on the item upon which an earth connection can be made. In addition the invention enables proper earth continuity to be achieved in existing installations which at present do not comply with the regulations.

The invention is not limited to the specific embodiments described and many variations and modifications are possible.

Claims (16)

1. An earthing connector comprising an apertured body adapted to fit around a part to be earthed projecting through the wall of electrical equipment and means for reducing the area defined within the apertured body for tightening the body onto said projecting part.

2. An earth connector as claimed in Claim 2 wherein the apertured body comprises a plurality of parts.

3. An earth connector as claimed in Claim 2 wherein at least two of the parts are hinged together.

4. An earthing connector as claimed in any preceding claim wherein the apertured body comprises an annulus.

5. An earthing connector as claimed in Claim 4 wherein the annulus is split.

6. An earth connector as claimed in Claim 1 or Claim 2, wherein the apertured body comprises a U-shaped member and a yoke connectable to the arms of the U-shaped member.

7. An earthing connector as claimed in any of Claims 2 to 6, wherein means are provided for moving adjacent parts of the apertured body so as to change the area enclosed thereby.

8. An earthing connector as claimed in any preceding claim and comprising a terminal for an earth connection.

9. An earthing connector as claimed in any preceding claim, wherein means are provided in the apertured body for engaging in the part to be earthed when said apertured body is tightened around the part to be earthed.

10. An earth connector as claimed in any preceding claim, wherein the edge of the apertured body defining the aperture is profiled so as to be receivable in a profiled part of the part to be earthed.

11. An earthing connector substantially as described herein with reference to Fig.l, 3, 4 or 5 of the accompanying drawings.

12. An assembly comprising a housing, an electrically conductive member extending through the housing, and an earthing connector as claimed in any preceding claim fixed to the part of the member that projects into the housing.

13. An assembly as claimed in Claim 12, wherein the housing is electrically non-conductive at least in part.

14. An assembly as claimed in Claim 13, wherein the member extends through a non-conductive part of the housing.

15. An assembly as claimed in Claim 12 wherein the earthing connector is spaced from the housing.

16. An assembly substantially as described herein with reference to Fig.2 of the accompanying drawings.