GB2325792A - Joint between power enclosure and conduit - Google Patents

Abstract

A joint comprises a threaded tubular coupling piece (10) screwed at one end onto a conduit 22 and secured at its other end to the wall (40) of a power enclosure (30) preferably by one or more bosses (18) having apertures (20) for receiving bolts to the enclosure wall. A bush (42) may be screwed into the bore from within the enclosure to bear against an earthing washer (46).

Description

ELECTRIC CONDUIT SUPPORT This invention relates to a conduit joint to carry power cables out of and into enclosures and is particularly concerned to provide an improved joint at terminations in enclosures where the conduit cannot be adequately supported.

There is a need to provide an improved, safer and reliable means of connection for such enclosure terminations, 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. The present invention is particularly applicable to the joining of a conduit to a termination box and although it is not necessarily limited thereto, it will be described below with particular reference to that situation.

Accordingly the invention provides in one aspect a joint between an electrical power enclosure and a conduit, the joint comprising a an electrical power enclosure and a conduit, the joint comprising a coupling piece having a threaded, axially-extending bore aligned with an aperture in a wall of the power enclosure and screwed onto the conduit at one end of the coupling piece, the other end of the coupling piece having at least one radiallyextending portion secured against the wall of the power enclosure by fixing means extending through the radially-extending portion to the wall of the power enclosure.

Preferably the radially-extending portion lies against the exterior of the wall of the power enclosure and a threaded bush extending from the interior of the power enclosure is threaded into the bore and bears against and makes direct electrical contact with a conductive insert which is connectable via a circuit protective conductor to the earth system of an electrical installation.

This feature enables the functions of earthing and mechanical support to be separated.

In one embodiment the coupling piece is arranged to carry a power cable between the enclosure and conduit, the piece having at least one outwardlyextending boss at a first end of the bore whereby it can be mounted on a wall of the enclosure and having an internal screw thread adjacent the first end, whereby the first end may abut one side of a wall of the enclosure around an orifice in that wall, an externally-threaded male bush screwed into the first end of the bridging piece from the opposite side of the wall of the enclosure and a conductive washer inserted between the bush and said wall and an end of the conduit being received in the jointing conduit coupling piece, whereby the conductive washer is connectable via a circuit protective conductor to the earth system of an electrical installation.

Other preferred features are defined in the dependent Claims, In another aspect the invention also provides a kit of parts to provide a joint between an electrical power enclosure and a conduit. In one embodiment the kit comprises a coupling piece having an axially-extending bore and at least one outwardly-depending boss at a first end of the bore whereby it can be mounted on a wall of an enclosure, and having an internal screw thread adjacent that first end, and an externally-threaded male bush to thread into the first end of the conduit piece and a conductive washer.

The kit may also include a circuit protective conductor and means to connect the conductor to a requisite earth terminal.

The enclosure may be metallic or non-metallic. For example, the conduit may be of steel and the enclosure may also be of metal but with a plastics coating, e.g. of epoxy resin paint. The invention is particularly useful for metal enclosures having non-screwed clearance holes for the conduit. For example, the enclosure may be a 13 amp metal socket outlet box.

The invention is particularly useful for enclosure/conduit joints where the conduit cannot be supported near to the enclosure, e.g. because of the conduit lying at a height between, say, girders in a factory or above suspended ceilings. Without adequate support adjacent to a termination the joint may suffer mechanical strain by, for example, being knocked by workmen, e.g. painters, plumbers and pipefitters, working in the vicinity and may, therefore, fail. The present invention gives the necessary support fully to meet any applicable regulations, e.g. the regulations of BS 7671.

The bosses on the conduit coupling piece to provide mounting of the piece on an enclosure may be, for example, three equi-spaced bosses around its end periphery but it may be found desirable or necessary to have a higher or smaller number. However, if desired the bosses may be in the form of a continuous peripheral flange. Clearance holes drilled or otherwise formed in the boss(es) provide attachment means using, e.g. bolts, to clamp the conduit coupling piece to the wall of the enclosure with its bore in alignment with a hole in the wall.

Embodiments of the invention will now be described with reference to the accompanying drawings in which: Figure 1 is an end elevation of a hollow bridging piece of the invention; Figure 2 is a longitudinal view of the piece of Figure 1; Figure 3 is a diagrammatic representation of one specific arrangement of conduit termination according to the invention; and Figure 4 is an enlarged view of a conduit/enclosure termination from Figure 3.

In Figures 1 and 2 a coupling piece 10 comprises a sleeve portion 12 having an axial bore 14 formed with an internal screw thread 16. At one end sleeve 12 carries 3 equi-spaced, outwardly-extending bosses 18, each boss having a hole 20 through which it may be bolted to an enclosure wall.

In Figure 3 a first steel conduit 22 runs vertically up the inside of a wall 24 of a building 26. Conduit 22 is coupled at 36 to a second steel conduit 22A which continues up the wall and turns at right angle near the top of the wall to run inside the building just underneath its ceiling or roof 28.

The conduit terminates at its upper and lower ends respectively in enclosure boxes 30 and 32. It is attached to wall 24 by conventional conduit saddles 34.

As shown more clearly in Figure 4, the coupling piece 10 is in position terminating a steel conduit 22 at a wall section 40 of an enclosure 30.

Conduit 22 extends into the bore 14 of the secured flange coupling piece 10.

A bush 42 having an enlarged head portion 44 and an externally-threaded length portion is passed through a hole in wall 40 of enclosure 30. Bush 42 is threaded into the bore 14 of piece 10 with a conductive washer 46 clamped between the head of the bush and the wall. The portion of bush 42 extending into bore 14 terminates short of the end of conduit 22 in the bore.

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 wall.

Washer 46 has a protruding arm 46A 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.

The conduit/enclosure connection is very firmly supported so that the circuit protection is far less likely to be broken accidentally.

It will be appreciated that the invention is not limited to the embodiments shown. Any suitable configuration of boss or flange may be used, e.g.

triangular, square or hexagonal, to ensure the fixing can adequately take any envisaged strains to maintain the joint in condition to conduct fault current to earth. The secured flange coupling 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 washers and bushes, although preferably of brass or copper, may similarly be of other electricallycompatible materials.

Claims (13)

1. A joint between an electrical power enclosure and a conduit, the joint comprising a coupling piece having a threaded, axially-extending bore aligned with an aperture in a wall of the power enclosure and screwed onto the conduit at one end of the coupling piece, the other end of the coupling piece having at least one radially-extending portion secured against the wall of the power enclosure by fixing means extending through the radially-extending portion to the wall of the power enclosure.

2. A joint as claimed in Claim 1, wherein the radially-extending portion lies against the exterior of the wall of the power enclosure and a threaded bush extending from the interior of the power enclosure is screwed into the bore and bears against and makes direct electrical contact with a conductive insert which is connectable via a circuit protective conductor to the earth system of an electrical installation.

3. Ajoint as claimed in Claim 2, wherein the conductive insert is a washer having a tab for connection to the circuit protective conductor.

4. A joint as claimed in any preceding Claim, wherein the radially extending portion is in the form of one or more bosses.

5. A joint as claimed in Claim 4, wherein there are three such bosses.

6. A joint as claimed in any of Claims 1 to 3, wherein the radially extending portion is in the form of a flange.

7. A joint as claimed in any preceding Claim, wherein the fixing means comprises one or more bolts extending through respective aperture(s) or cut-outs in the or each radially-extending portion.

8. A joint as claimed in Claim 2 or any of Claims 3 to 7 as dependent thereon, wherein the power enclosure has an electrically insulating coating in contact with the radially-extending portion.

9. A joint between an electrical power enclosure and a conduit, the joint being substantially as described hereinabove with reference to Figures 1 to 3 of the accompanying drawings.

10. A kit of parts for a joint as claimed in any preceding Claim, the kit comprising a coupling piece as defined in any of Claims 1,4,5 and 6 and fixing means capable of being fitted through one or more apertures or cut-outs in the radially-extending portion to secure the coupling piece to the wall of a power enclosure.

11. A kit as claimed in Claim 10, further comprising an externally threaded bush for screwing into said bore.

12. A kit as claimed in Claim 11, further comprising an electrically conductive washer capable of being secured in contact with the bush and having a tab for electrical connection to an earthing system.

13. An electrical installation comprising at least one power enclosure and conduit connected by a joint as claimed in any of Claims 1 to 9.