GB2325791A - Joint between two electrical power enclosures secured by bushes - Google Patents

Abstract

A joint between two electrical power enclosures (20,22) comprises a flanged coupling piece secured to the enclosures by bushes (24,26) screwed into its bore and in turn securing and preferably providing electrical contact with conductive washers (28,30) having tabs (28A,30A) for connection to a circuit-protective conductor. The flanges (12) may have an insulating coating. The joint may be supplied as a kit.

Description

CIRCUIT PROTECTIVE CONDUCTOR JOINTS This invention relates to a joint between two enclosures to carry power cables and is particularly concerned to provide an improved joint for use as a circuit protective conductor.

There is a need to provide an improved, safer and reliable means of connection for such enclosures, which means is sufficiently robust to take a degree of mechanical strain, e.g. knocks, without loss of the capability to pass fault current safely to earth, which can be fitted readily in circumstances where the enclosures are close together and difficult to couple in normal onsite conditions.

Accordingly the invention provides in one aspect a joint between two electrical power enclosures, the joint comprising a coupling piece having an axiallyextending bore and a peripheral outwardly-extending flange at each end of the bore, the coupling piece having an internal screw thread at each end of the bore, the coupling piece being secured to the power enclosures by threaded bushes screwed into the bore with the flanges lying against the exterior of and surrounding orifices in the respective power enclosures, the bushes extending from the interior of the enclosures through the respective orifices.

The flanges provide excellent electrical shielding which is important in certain installations, e.g. in hospitals where there is electrical equipment sensitive to electromagnetic fields. Also the coupling piece can easily be fitted within confined spaces.

Preferably at least one bush is directly electrically connected to an earthing member secured in contact therewith, the earthing member being distinct from the power enclosure. Thus the enclosure and any internal electrical assembly may be effectively earthed.

In one embodiment the coupling piece is arranged to carry power cables between the two enclosures, the piece having a peripheral outwardly extending flange at each end of the bore and having an internal screw thread adjacent each end, whereby each end may abut one side of a wall of one enclosure about an orifice in that wall, an externally-threaded male bush screwed into each end of the piece from the opposite side of the wall and a conductive washer inserted between each bush and its respective wall, each conductive washer being connectable via a circuit protective conductor to an earth system.

In another aspect the invention also provides a kit of parts to provide a joint between two electrical power enclosures, the kit comprising a coupling piece having an axially-extending bore and a peripheral outwardly extending flange at each end of the bore and having an internal screw thread adjacent each end, and two externally threaded male bushes to thread into each end of the coupling piece.

The kit may also include two conductive washers. It may also include a pair of circuit protective conductors and means to connect those conductors to earth.

The enclosures may be metallic or non-metallic.

Further preferred features are defined in the dependant Claims.

The invention also provides an electrical installation comprising at least two electrical power enclosures connected by the joint of the invention.

The invention is particularly useful for the installation on site of conduit power systems, e.g. based on steel conduits, and for systems where a conduit terminates into a metal enclosure. Such enclosures frequently have plastics coatings, e.g. of epoxy resin paint finish, and non-screwed clearance holes for conduit entry in use. The invention ensures a safe, reliable, protected joint for such systems. The enclosures may be, for example, 13 Amp metal socket outlet boxes.

The joint provided by the invention establishes full cross-sectional area contact between the jointing piece and the enclosures, thereby establishing fault current canying capacity fully to regulatory levels, e.g. Regulation 543-1 of the current British Wiring Regulations now issued as BS 7671.

The invention is particularly useful when two enclosures to be joined are so close together on site that it is difficult or impossible to cut a piece of steel conduit to the required length and then screw it to join the two enclosures.

The hollow jointing conduit coupling piece of the invention may be produced in a length corresponding to that of existing conventional conduit couplers and may also be produced in a range of different lengths to meet different, particular circumstances.

Embodiments of the invention will now be described by way of example only with reference to the accompanying drawings in which: Figure 1 is a plan view of a coupling piece of the invention; Figure 2 is an end view in the direction of arrow A of Figure 1; and Figure 3 is a longitudinal view of a pair of enclosures joined by a joint of the invention.

In Figures 1 and 2 a jointing conduit coupling piece 10 comprises a length of pipe which is circular in cross-section and has an outwardly-extending annular flange 12 at each end of its length 'x'. Its maximum external diameter 'y' nominally corresponds to the diameter of a circuit protective conductor (cpc) washer which is to be fitted inside an enclosure (see Figure 3).

('y' may be a lesser diameter as may be required to suit any specific enclosure.) Piece 10 has a bore 14 of diameter 'z' screw threaded to correspond, e.g. to the standard steel conduit sizes of 16.0, 20.0, 25.0 mm etc. As indicated above, sox' may be equivalent to the length of a standard conduit coupling or any other desired length. 'z' is a standard conduit entry size to correspond to a conduit entry hole in the wall of an enclosure where the joint is to be provided. Thus 'y', for example, may correspond to the dimensions indicated in BS 4568, Part 2, 1970 but may be larger or smaller, as required. 'y", is sufficiently large to ensure adequate bearing surfaces against the wall of an enclosure. The end faces 16 of each flange 12 are machined or formed to provide a bearing surface to be disposed flush against an enclosure wall.

The piece 10 is internally screw-threaded (not shown) for at least a portion of bore 14 adjacent each end of the bore.

In Figure 3, the coupling piece 10 is shown in position joining two enclosures 20 and 22. A bush 24 having an enlarged head portion 24A and an externally-threaded length portion 24B is passed through a hole in a wall 20A of enclosure 20. Bush 24 is threaded into one end of the bore 14 of piece 10 with a conductive washer 28 being positioned to lie between the head of the bush and its respective wall. The other end of piece 10 is then attached in the same manner about a hole in a wall of enclosure 22 using a bush 26 having an enlarged head portion 26A and an externally-threaded length portion 26B.

A conductive washer 30 is similarly positioned to lie between head 26A and its respective wall.

The joint between the two enclosures is thereby securely and reliably made.

Power cables may be passed through piece 10 into and out of the enclosure and may be inserted through the bore of piece 10 after the piece is connected to the enclosure wall and fixed in position in the electrical installation.

Each conductive washer 28, 30 has a protruding arm 28A, 30A which may conveniently be connected by a conventional conductor (not shown) to make effective connections to the earth terminals of an enclosure and/or an internal electrical accessory or assembly. The earth connection may be made, for example, as shown in GB 2194860.

It will be appreciated that the invention is not limited to the embodiments shown. The external profile in end view of the jointing conduit piece need not be circular. Other profiles, e.g. hexagonal, may be used. The jointing conduit piece, although preferably made of steel or cast iron, may, if desired, be of other electrically compatible metals or other material, e.g. metal-impregnated plastics materials. The end faces of the conduit coupling pieces may be formed or swaged instead of machined. The washers and bushes, although preferably of brass or copper, may similarly be of other electrically-compatible materials.

Claims (12)

1. A joint between two electrical power enclosures, the joint comprising a coupling piece having an axially-extending bore and a peripheral outwardly-extending flange at each end of the bore, the coupling piece having an internal screw thread at each end of the bore, the coupling piece being secured to the power enclosures by threaded bushes screwed into the bore with the flanges lying against the exterior of and surrounding orifices in the respective power enclosures, the bushes extending from the interior of the enclosures through the respective orifices.

2. A joint as claimed in Claim 1, wherein at least one bush is directly electrically connected to an earthing member secured in contact therewith, the earthing member being distinct from the power enclosure.

3. A joint as claimed in Claim 2, wherein the earthing member is a conductive insert secured between a head of the bush and the facing interior surface of its power enclosure.

4. A joint as claimed in Claim 3, wherein the conductive insert is a conductive washer.

5. A joint as claimed in Claim 4, wherein the washer has a tab portion for connection to a circuit protective conductor.

6. A joint as claimed in any of Claims 2 to 5, where, at least one of the flanges bears against an insulating coating on the exterior of the power enclosure.

7. A joint as claimed in any of Claims 2 to 5, wherein at least one of the enclosures is non-metallic.

8. A joint between two electrical power enclosures the joint being substantially as described hereinabove with reference to Figures 1 to 3 of the accompanying drawings.

9. A kit of parts for a joint as claimed in any preceding Claim, the kit comprising a coupling piece having an axially-extending bore and a peripheral outwardly-extending flange at each end of the bore and having an internal screw thread at each end, and two externally threaded male bushes to thread into each end of the coupling piece.

10. A kit as claimed in Claim 9, further comprising two conductive washers having respective tab portions for connection to circuit protection conductors.

11. A kit as claimed in Claim 10, further comprising at least one circuit protective conductor.

12. An electrical installation comprising at least two electrical power enclosures connected by a joint as claimed in any of Claims 1 to 8.