GB2349990A

GB2349990A - Clamp for connecting to edge of bus bar

Info

Publication number: GB2349990A
Application number: GB9910988A
Authority: GB
Inventors: Keith Wray Ball; Kenneth Neill
Original assignee: Schneider Electric Ltd; Schneider Ltd
Current assignee: Schneider Electric Ltd
Priority date: 1999-05-13
Filing date: 1999-05-13
Publication date: 2000-11-15
Also published as: GB9910988D0

Abstract

A clamp for making a connection to a bus bar 10 consists of an outgoing conductor 18 and a clamping nut 28, which form a pair of jaws 26. The jaws can be positioned at any point along the edge of the bus bar, and are then drawn together by a bolt 24. The clamping nut 28 may be screw-threaded and hold the bolt 24. The jaws may have serrations (see figure 6). Alternatively, the clamp may consist of a single portion and the screw may run parallel to the bus bar and cut into it (see figure 10).

Description

2349990 ELECTRICAL DISTRIBUTION APPARATUS AND CLAMP FOR USE THEREIN

Introduction

The invention relates to electrical distribution apparatus including at least one bus bar comprising a length of generally flat conductive bar of uniform cross-section, and at least one outgoing conductor electrically and mechanically connected to the bus bar. The invention relates in particular to making fixed outgoing connections to bus bars, in electrical Panel boards and switchgear, although it may be applied across the whole range of distribution apparatus. The term panel, board may be used conveniently to refer to apparatus in which bus bars are designed for currents approximately in the range 250A to 800A, while apparatus for currents higher than 800A tends to be referred to as switchgear.

Particularly when bus bars and outgoing conductors are carrying such currents, connections to the bus bars need to be of high mechanical strength to withstand the strong mechanical forces which can occur during electrical short circuit conditions. Further, although the conductors comprise substantial metalwork, the conductors and their connections undergo significant thermal excursions in normal operation.

One known method of making connections to bus bars in such apparatus involves drilling holes in the bus bar at desired outgoer positions, and then bolting on copper conductors, which are subsequently bolted to the outgoing electrical devices.

Such devices will typically comprise circuit breakers, each breaker feeding an individual load circuit. Clearly the requirement for these holes involves additional expense, limits the positions at which connections can be made to pre-set positions, and degrades the performance of the bus bar.

Another known method of connecting such outgoers to bus bars is to provide resilient plug-on finger connectors, attached directly to the circuit breaking devices which grip the edge of the bus bar by spring force. Due to thermal 2 expansion/contraction a finger contact may lose its resilience with age, thus allowing deterioration to occur due to heating/oxidising effects. This could lead to a high resistance joint and ultimate bum out.

The invention aims to provide an alternative method of connecting conductors to bus bars, particularly one which is suitable for high-current apparatus such as panel boards and switchgear, and one which preferably avoids one or more of the above drawbacks of the known methods.

The invention provides an electrical distribution apparatus including at least one bus bar comprising a length of generally flat conductive bar of uniform cross section, and at least one outgoing conductor electrically and mechanically connected to the bus bar at a desired position along the length of the bus bar by means of a rigid clamp having jaws either side of one edge of the bus bar.

The clamp can be freely positioned on a plain bus bar, and yet can provide a solid connection, with the required electrical and mechanical integrity.

In a preferred embodiment, the jaws are held rigidly opposed around the edge of the bus bar by means of a screw coupling. The screw coupling may include a threaded bolt extending through a bore in at least one of the jaws and between the jaws in a direction verse to both the length and width directions of the bus bar, so as to draw the jaws tightly together.

One of said jaws may be formed integrally with at least part of said outgoing conductor, while a second one of said jaws is formed by a separate clamping block urged toward the first jaw by said screw coupling.

The clamping block may have a shaped profile, so as to contact the bus bar on one side of an axis of the screw coupling, and to contact part of the first jaw to the other side of said axis, the point of contact with the first jaw acting as a fulcrum.

3 The clamping block may comprise a nut having a threaded bore.

Various alternative embodiments and further optional features and combinations of features are defined in the appended claims, and in the detailed embodiments which will now be described.

Brief Description of the Drawings

Embodiments of the invention will now be described in detail, by way of example only, with reference to the accompanying drawings, in which:

Figure I shows part of an electrical switchgear assembly including clamped outgoing connections according to a first embodiment of the invention; Figure 2 shows a nut portion of one of the clamp connections in the assembly of Figure I in (a) side elevation and (b) top plan view; Figure 3 shows an example of an outgoing connector forming part of the clamp assembly, in (a) side elevation and (b) bottom plan view; Figure 4 shows a modification of the connector of Figure 3, in (a) side elevation and (b) bottom plan view; Figure 5 shows in side elevation a clamping assembly according to a second embodiment of the invention; Figure 6 shows a nut of the assembly of Figure 5 in (a) side elevation and (b) top plan view; Figure 7 shows a retainer part of the assembly of Figure 5 in (a) side elevation, (b) top plan view and (c) rear elevation; 4 Figures 8 and 9 show alternative forms of conductor according to a third embodiment of the invention in (a) side elevation, (b) top plan view and (c) rear elevation (Figure 9 only); and Figure 10 shows a conductor with integrated clamp according to a fourth embodiment of the invention, in (a) side elevation and (b) rear elevation.

Detailed Description of the Embodiments

Figure I shows part of a switchgear assembly, in which a stack of four main bus bars 10 are arranged in an enclosure 12, for the distribution of neutral (N) and three live phases of electrical power. The main bus bars 10 are shown in cross section, and run parallel with one another into and out of the plan of the drawing.

Insulating spacers 14 are provided to maintain separation of the bus bars. At the right hand side of the figure, a circuit breaker 16 (part only shown) is mounted, and is connected electrically to each of the main bus bars 10 by rigid conductors 18.

Each of the outgoing conductors 18 is connected to a respective bus bar 10 by means of a clamp assembly 20, which grips the edge 22 of the bus bar 10 at any desired position. The edge of the bus bar is not modified in any way to receive the clamp. Each clamp assembly 20 comprises a pair ofjaws held together by the force of a threaded bolt 24. In the present embodiment, a first jaw 26 is formed by the end of the outgoing conductor 18 itself which has a hole for passage of the bolt 24. The second jaw is formed by a separate clamping nut 28, comprising a specially shaped block with a threaded hole which is engaged by the thread of the bolt 24. A compression washer 30 (such as a Belleville washer) is included between the head of the bolt and the end of the conductor 26.

The electrical and mechanical connection between conductor 18 and main bus bar 10 is thus effected by placing the edge 22 of the bus bar between the jaws of the clamp assembly, and tightening the bolt 24 to bring the jaws together on either side of the main bus bar 10. An optional lead-in chamfer 264 assists in mounting the clamp on the bus bar. Compression washer 30 absorbs thermal expansions of the parts during operation, maintaining a strong mechanical and hence electrical connection.

Figure 2 shows the nut 28 of the clamp assembly in more detail. The nut comprises a metal block which is rectangular in plan view (b) with a stepped profile (a). The block is arranged to stand off slightly from the surface of the outgoing conductor 18/26 around the axis of the bolt 24, the force of the screw tightening being taken firmly on the bus bar, between a clamping surface 282 and the other jaw 26 formed by the outgoing conductor 18. The rear end 284 engages the jaw 26 and acts as a fulcrum.

Figure 3 shows the jaw 26 formed by the end of the outgoing conductor 18, in more detail. Although a short straight section of conductor is shown, it will be clear from a consideration of Figure I that the length and form of the outgoing conductor 18 will be adapted to suit the desired routing of current. In addition to bore 262 which receives the bolt 24 of the clamp assembly, another bore 182 is provided at the far end of the outgoing conductor 18, for connection to the terminals of the circuit breaker 16 or other outgoing device.

Figure 4 shows a modification of the conductor of Figure 3, in which two small lugs 266 are formed by pressing out the metal, which serve to prevent the nut 28 ftom turning during tightening of the bolt.

In this and the other embodiments it will be understood that all parts are made from conductive metal with the appropriate strength characteristics. In particular, the main bus bars 10 and outgoing conductors are typically made of high conductivity copper. The nuts 28 may be made of copper or more probably steel.

Figure 5 shows in elevation a single clamp assembly according to a second embodiment of the invention, this corresponds closely in form to the assembly of Figures I to 3 and the same reference and numerals are used to refer to corresponding 6 parts. The jaw fortned by the nut 28 in this embodiment is extended with a lead-in chamfer 289 to ftu-ther facilitate assembly of the clamp onto the main bus bar 10. Additionally in this embodiment, a retainer 32 is provided, which prevents the nut 28 from rotating during tightening of the bolt 24.

Figure 6 shows the nut 28 of the Figure 5 embodiment in more detail. The clamping surface 284 is provided with serrations, as can be seen. Particularly, when the clamp nut 28 is made of steel, these will bite into the softer copper bus bar, adding to the security of the mechanical and electrical connection.

Figure 7 shows the retainer 32 in more detail. This can be formed from mild steel. A flat body portion 320 is formed with a bore 322, so that it may sit around the bolt shaft between the compression washer and the outgoing conductor end 26 (Figure 5). Side portions 324 are formed bending down on the body portion 320, which pass either side of the copper bar 18 and nut 28 (Figure 5). Additionally, extensions 326 of the side portions reach down the side of the nut 28, to prevent the nut moving out of alignment when tightening.

The above embodiments comprise separate parts held together by a screw tensioning means, which form the jaws of the clamp. One of the jaws is formed by the outgoing conductor 18, while the other is formed by a clamping block, nut 28. It will be understood that other arrangements comprising two or more parts in addition to the outgoing conductor 18 are possible in principle. It is also possible in principle to provide the threading in the conductor 18, rather than the block (nut) 28, or to provide a separate nut in addition to the block 28. The arrangements shown are preferred, however, for their mechanical and electrical integrity, and simplicity of manufacture and assembly.

Figures 8 to 10 show ftirther embodiments of the invention, in which both clamp jaws are integrally formed in one piece, which may or may not be integral also with part of the outgoing conductor.

7 In Figure 8, clamp 800 is provided by a single piece of copper or other metal, formed to provide a pair of jaw surfaces 802 and 804, between which the edge of the main bus bar 10 will fit relatively snugly. Leading edges of the jaws are radiused at 806 and 808 to facilitate assembly onto the bus bar. Bores 810 and 812 are formed in the jaws, for the passage of the clamp tightening bolt (not shown). One of the bores may be threaded or a separate threaded nut (not shown) may be used to complete the clamping. As in the earlier embodiments, the compression washer is included, to maintain a strong mechanical and electrical connection throughout the normal temperature excursions of the bus bar and outgoing conductor. At the tail end of the clamp, another bore 814 is provided for making the ongoing electrical connection, either to a circuit breaker or to an intermediate outgoing conductor.

Figure 9 shows a clamp virtually identical to that of Figure 8 with the tail end carrying aperture 814 to provide for termination at a different orientation.

Figure 10 shows another form of clamp in which the jaws are formed integrally with the outgoing conductor, or separate clamp piece. A first jaw 100 fits beneath the edge of the bus bar 10, while a second jaw 102 fits above it. A threaded bore 104 is formed in the second jaw 102, running parallel to the surface of the main bus bar, and partially intersected by the surface of the main bus bar. A bolt 106 inserted and screwed into this bore 104 consequently engages and cuts by its thread into the surface of the bus bar 10, perfecting the mechanical and electrical connection.

In particular, the clamp is retained on the bus bar, while the bus bar is pressed against the lower jaw 100. A compression washer 108 is provided beneath the head of the bolt 106.

The one-piece clamps of Figures 8 to 10 can be formed ftom simple copper or other metal extrusions, sawn and drilled as necessary.

It will be appreciated that all of the embodiments described are merely examples, and the invention will encompass many variants and modifications in addition to those explicitly disclosed herein.

Claims

1. Electrical distribution apparatus including at least one bus bar comprising a length of generally flat conductive bar of uniform crosssection, and at least one outgoing conductor electrically and mechanically connected to the bus bar at a desired position along the length of the bus bar by means of a rigid clamp having jaws either side of one edge of the bus bar.

2. Apparatus as claimed in claim 1, wherein said jaws are held rigidly opposed around the edge of the bus bar by means of a screw coupling.

3. Apparatus according to claim 2, wherein said screw coupling includes a threaded bolt extending through a bore in at least one of the jaws and between the jaws in a direction transverse to both the length and width directions of the bus bar, is and draws the jaws together against opposite faces of the bus bar when tightened.

4. Apparatus as claimed in claim 2 or 3, wherein a first one of said jaws is formed integrally with at least part of said outgoing conductor, and a second one of said jaws is formed by a separate clamping block urged toward the first jaw by said screw coupling.

5. Apparatus as claimed in claim 4, wherein said clamping block has a shaped profile, so as to contact the bus bar on one side of an axis of the screw coupling, and to contact part of the first jaw to the other side of said axis, the point of contact with the first jaw acting as a fulcrum.

6. Apparatus as claimed in claim 4 or 5, wherein said clamping block comprises a nut having a threaded bo&.

7. Apparatus as claimed in claim 4, 5 or 6, further comprising means for restraining the clamping block against rotation during tightening of said screw coupling.

9

8. Apparatus as claimed in claim 7, wherein said restraining means comprises one or more projections formed integrally with the firstjaw.

9. Apparatus as claimed in claim 7, wherein said restraining means comprises a separate part, formed also to restrain an end of the block remote from the bus bar in proximity with the first jaw, when the screw coupling is in a loosened state.

10. Apparatus according claim 2, wherein a threaded bolt is carried by one of the jaws and extends in a direction transverse to the length direction of the bus bar and generally parallel to the width direction of the bus bar and wherein one side of the bolt engages the surface of the bus bar with a portion of its thread.

11. Apparatus as claimed in any of claims 2 to 10, wherein said screw coupling incorporates a compression washer to accommodate thermal expansion of the clamp and bus bar.

12. Apparatus as claimed in any preceding claim, wherein both jaws are formed integrally in a single piece of conductive material.

13. Apparatus as claimed in claim 12, wherein said jaws are formed as parts of a metal extrusion.

14. Apparatus as claimed in any preceding claim, wherein at least one of the jaws is formed integrally with at least a portion of the outgoing conductor.

15. Apparatus as claimed in any preceding claim, wherein at least one of the jaws of the clamp is provided with serrations adapted for biting into the surface of the bus bar.

16. Apparatus as claimed in any preceding claim, wherein said outgoing conductor comprises a length of generally flat conductive bar.

17. Apparatus according to any preceding claim, wherein the maximum rated current in the bus bar exceeds 250 amperes.

18. A clamp specifically adapted for use as the clamp in the electrical distribution apparatus of any of the preceding claims.