GB2362270A

GB2362270A - Improvements in and relating to electrical trunking

Info

Publication number: GB2362270A
Application number: GB0011271A
Authority: GB
Inventors: Pertti Paasi
Original assignee: Caradon MK Electric Ltd
Current assignee: Caradon MK Electric Ltd
Priority date: 2000-05-10
Filing date: 2000-05-10
Publication date: 2001-11-14
Anticipated expiration: 2020-05-10
Also published as: GB2362270B; GB0011271D0

Abstract

An electrical trunking (1) comprises a longitudinal base (12) and at least a first and a second longitudinal cover (14, 16) and a resilient clip (10) (arranged to releasably retain both the first and the second covers to the base. The resilient clip provides electrical connection between the base and each of the covers, and is retained to the base by means of a first set of teeth (346, 348) disposed longitudinally along two opposed edges of the clip. The base has an upstanding wall protruding (220) between opposed legs (308, 310) of the clip, and the upstanding wall is arranged to maintain the engagement of the first set of teeth with the base. A second set of longitudinally disposed teeth (320) are provided on the clip, and both sets of teeth are arranged to cut into the surfaces of the respective base or covers so as to establish the electrical connection.

Description

2362270 Improvements in and relating to electrical trunking The present

invention relates to electrical trunking made of an electrically conductive material, and to means for ensuring electrical continuity between component parts of the trunking.

Electrical trunking for receiving electrical cables in an electrical wiring installation is well known. Such trunking frequently comprises a base and a cover. In order to ensure safety and to protect against electromagnetic radiation it is important to ensure a good electrical connection between the cover and the base. Frequently the cover is secured to the base by means of screws, which ensures the necessary good electrical connection. However, a disadvantage of this is that the use of screws places constraints on the design of the trunking components and increases the cost of manufacture and installation. Where steel trunking is used, the resilience of the components may be such that a cover may be arranged to snap fit onto a base, with a sufficiently tight interference fit so that an adequately good electrical connection may be obtained. A problem with this is that such trunking is generally limited to small cross sections to obtain sufficient contact pressure at the snap fit to provide the adequately good electrical connection.

2 In EP 0 469 457 to Ackermann a sheet metal trunking or wall channel is shown, the trunking comprising a wall duct rear member 40 and a cover member 30, with a resilient holding clip 10. In many of the figures of this Ackermann patent the retention of the cover to the base could be adversely affected by the difficulty in maintaining necessary tolerances on the folded or rolled base and cover sections. Another disadvantage of the arrangement shown in Ackermann is the difficulty of manufacturing the clip, which is formed in several planes. A further disadvantage is that the long clip arm 19, which provides resilient support for the gripping points 13, 14 and 15 does not ensure that the cover is positively retained to the rear member. Such an arrangement would not necessarily meet a safety requirement, for many installations of such trunking, that it is necessary to use a tool to remove the cover, since removal of the cover may provide access to exposed electrical conductors.

In German Gebrauchmuster 77 01 100 to Kleinhuis, a trunking is provided with a resilient clip 20 to retain a cover 17 to a base channel. The arrangement shown in Kleinhuis does not provide means for ensuring good electrical contact with the base channel, and does not 25 provide positive retention of the cover to the base. A further disadvantage of the Kleinhuis arrangement is that the clip is retained to the cover, where it is more vulnerable to becoming lost or misplaced when the cover is removed temporarily to provide access to the enclosed 30 space.

According to the invention there is provided an electrical trunking comprising a longitudinal base and at least a first and a second longitudinal cover and a resilient clip arranged to releasably retain both the first and the second covers to the base, the resilient clip providing electrical connection between the base and each of the covers, the resilient clip being retained to the base by means of a first set of teeth disposed longitudinally along two opposed edges of the clip, the base having an upstanding wall protruding between opposed legs of the clip, the upstanding wall arranged to maintain the engagement of the first set of teeth with the base, a second set of longitudinally disposed teeth on the clip, both sets of teeth being arranged to cut into the surfaces of the respective base or covers so as to establish the electrical connection.

A benefit of the invention is that the cover may be retained to the base without the use of screws. A further benefit is that the cover may be retained to the base without either component being resilient.

A further benefit is that the clip is less vulnerable to becoming accidentally detached and lost while mounted to the base, which would normally be attached to a firm, immovable substrate, such as the wall of a building.

4 Preferably one cover may removed from the base, leaving the other cover retained to the base.

A benefit of this is that one cover may be removed with out removing the other. This is advantageous where one compartment is being used for low voltage wiring, such a computer network cables, and another compartment is being used for mains voltage power cables. Hence the safe access may be provided to one compartment, while another compartment remains covered.

Preferably the resilient clip is arranged to provide a good electrical connection between the cover and the base. Preferably a resistance of the electrical connection is less than 1/10 ohm. More preferably the resistance is less than 1/loo ohm. Still more preferably the resistance is less than 1/1000 ohm.

A benefit of a good electrical connection with a low value of resistance is that electrical safety is improved, since a hazard arising from a risk of electrocution from touching trunking components at different potentials arising from an electrical fault are reduced.

Preferably the resilient clip has means arranged to provide high contact pressures to ensure good electrical contact.

Preferably the means arranged to provide high contact pressures comprise resilient protrusions from the resilient clip.

Preferably the means arranged to provide high contact pressure further comprises sharp edges.

A benefit of resilient protrusions is that extremely high contact pressures may be obtained. A benefit of the resilient protrusions having sharp edges is that the extremely high contact pressures may be arranged so that the sharp edges penetrate a surface coating on the cover or base. Examples of such surface coatings would be oil, anodising, or paint.

A further benefit of a good electrical connection with a low value of resistance is that improved protection against electromagnetic radiation is achieved by ensuring that any such radiation may be prevented by induced currents flowing in and between the cover and base.

In an embodiment of the invention the cover and base are made of metal.

In another embodiment of the invention the cover and base are made of a plastics material, which has an electrically conductive surface, on at least an inside surface of the trunking and including the connecting means of each of the base and the cover.

6 SPecif ic embodiments of the invention will now be described by way of example with reference to the accompanying drawings in which:- Figure 1 is an end view of an electrical trunking according to the invention; Figure 2 is an enlarged view of a part of the trunking shown in Figure 1; Figure 2A is the same enlarged view as that of Figure 2, of a part of the trunking shown in Figure 1, showing a resilient clip, but with the covers removed; Figure 3 is an end view of the resilient clip shown in Figure 1; and Figure 4 is a perspective view of the resilient clip shown in Figure 1.

From Figure 1, an end view of an electrical trunking 1 is shown, which comprises a base 12, a top cover 14, a centre cover 16 and a bottom cover 18 and base extension 20, each of which covers combine with the base to form respectively an enclosed top space 24, an enclosed centre space 26 and an enclosed bottom space 28. The enclosed 7 spaces may receiving electrical cables, electrical busbars, or other services such as optical fibres, or air or water pipes. The trunking 1 is of indefinite length, and would normally form a part of a trunking system which would include other components such as corner fittings and end fittings which are not shown. A top cable retainer 34 is fitted within the enclosed space 24, and a centre cable retainer 36 is fitted within the enclosed centre space 26. The cable retainers may be of short length, for example 35mm long, and fitted at intervals as required along the trunking. Base 12 comprises a back wall 40 for mounting to, a supporting surface (not shown), and upstanding side walls 42, 44, 46 and 48, and base extension 20 has a sidewall 50. Each of sidewalls 42 and 48 having a first connecting means 60 and 62 extending along a top edge 64 and 66 respectively, and sidewalls 44.and 46 having a second connecting means 70 and 72 extending along a top edge 74 and 76 respectively, and the sidewall 50 of the base extension 20 having a third 20 connecting means 80 extending along a top edge 82 of the sidewall 50. A resilient clip 10, is mounted to each of the second connecting means 70 and 72. Resilient clip 10 is of a finite short length, and a number of such clips may be fitted at intervals along each of the second 25 connecting means. Cover 14 comprises a front wall 140, along an edge 142 of which extends a 'fourth connecting means 144 and along an edge 146 a fifth connecting means 148 extends. Centre cover 16 comprises a front wall 160, along each edge 162 and 166 of which extends a sixth 30 connecting means 164 extends. Bottom cover 18, is similar to centre cover 16, and comprises a front wall 180, along each edge 182 and 186 of which extends a sixth connecting means 184 extends.

From Figure 2A an enlarged view of the portion of the trunking fitted with the clip 10 may be seen. In Figure 2A, the trunking base 12 is shown in the condition with covers 14 and 16 removed. The second connecting means 70 comprises a pair of locating walls 210 and 212, each with a protrusion 214 and 216, and central wall 220. The clip 10 is mounted to the first connecting means such that a first set of teeth 346 and 348 engage the inner walls 222 and 224 respectively of locating walls 210 and 212. The teeth 346 and 348 are resiliently urged outwards SO that the teeth further located behind protrusions 214 and 216, retaining the clip to the base 12. The clip 10 has leading ramped portion 350 and 352 and retaining ramped portion 360 and 362. The central wall 220 provides further support and location to the clip 10, and is arranged to prevent the disengagement of the teeth 346 or 348 form behind the protrusions 214 or 216 respectively when a cover is mounted to the base 12 or removed from the base.

From Figure 2, the same enlarged portion of Figure 1 as described above with reference to Figure 2A may be seen with the covers 14 and 16 mounted to the base 12.

Locating walls 210 and 212 provide locations for the front covers 14 and 16 respectively. Cover 14 has limb 152 which engages with locating wall 210. Cover 16 has protrusion 168 which engages with locating wall 212. The resilient clip 10 urges each of the covers against their 9 respective locating wall. The engagement of the locating walls with the corresponding features on the covers, ensures that front faces 141 and 161 of the covers 14 and 16 form a flush joint along the length of the trunking 1.

The locating walls also ensure that gap 226 between the covers is closely controlled. A benefit of controlling the gap 226 closely is that safety is improved, since a small gap restricts use of a tool to remove a cover from the base. A further benefit is that the appearance of the installed trunking is improved.

A further benefit of the limb 152 on cover 14, is that this cover which is most likely to be mounted at the top of the trunking when installed is better able to resist displacement by any external pressure or contact applied 1S to an external surface of the front wall 140.

In use, as the cover 14 is moved in the direction of arrow 2X to mount the cover to the base 12, a curved wall contacts leading ramped portion 350 of the clip 10 resiliently deflecting the clip until the cover reaches the position shown in Figure 2 and Figure 1 such that the locating wall 210 is located in groove 154. The cover is then retained in this position by the curved wall 150 engaging the retaining ramped portion 360 of the clip 10.

The central wall 220 provides support to the resilient legs 308 and 310 of the clip 10 and enhances the retention of the covers by the clip.

Retention of the covers is enhanced by the support given by central wall 220 protruding between the opposed resilient legs 308 and 310 as each leg acts as a resilient beam, being deflected in the direction of 2L or 2L' respectively by covers 14 or 16 as the cover is mounted to, or removed from the base.

Similarly, as the cover 16 is moved in the direction of arrow 2X to mount the cover to the base 12, a curved wall 170 contacts leading ramped portion 352 of the clip 10 resiliently deflecting the clip until the cover reaches the position shown in Figure 2 and Figure 1 such that the 10 locating wall 212 is located against protrusion 168. The cover is then retained in this position by the curved wall 170 engaging the retaining ramped portion 362 of the clip 10. In use, the base 12 is mounted to a support surface with 15 the covers 14, 16 and 18 removed, once any electrical or other services have been placed in the spaces 24, 26 and 28, the covers 14, 16 and 18 are mounted to the base. Each cover engages with the base along each edge of the cover, so that fourth connecting means 144 of the cover 20 14 engages first connecting means 60 of the base 12 at edge 142, and fifth connecting means 148 engages with second connecting means 70 along the other edge 146. Likewise the sixth connecting means 164 of the cover 16 engages second connecting means 70 of the base 12 at edge 25 162, and sixth connecting means 164' engages with second connecting means 70 along the other edge 166. Likewise the sixth connecting means 184 of the cover 18 engages second connecting means 70 of the base 12 at edge 182, and sixth connecting means 184' engages with third connecting means 80 along the other edge 186.

Preferably the resilient clips 10 are arranged to resiliently and removably retain the cover to the base.

More preferably each of the covers is retained to the base such that once mounted to the base, a cover cannot be removed without the use of a tool.

From Figure 3, the clip 10 may be seen in an unstressed state. The clip is resiliently compressed in the direction of arrows 3Y as it is inserted into the connecting means 70 and 72 of the sidewalls 44 and 46.

From Figure 4, a perspective view of clip 10, the first set of teeth 346 may be seen to comprise many sharp edges is 364. Similarly first set of teeth 348 comprise many sharp edges 365. Resilient sheared flaps 320 and 322 visible in Figure 4 and 324 (visible in Figure 3) and 326 (not visible) have sharp edges 330, 331, 332 and 333 respectively, these sharp edges forming a second set of teeth. The resilient sheared flaps protrude a surface 328 and 329 of the clip.

The sharp edges 330, 331, 332 and 333 are resiliently urged to protrude the surfaces 328 and 329 respectively so that they cut into the surface of the respective covers 14 and 16 as the covers are mounted tothe 12 trunking establishing an electrical connection between the clip and the covers.

Hence, when for example the covers 14 and 16 are in the position shown in Figure 2, teeth 346 and 348 are bearing against the inner wall 222 and 224 and the sheared sharp edges 364 and 365 are such that they make good electrical contact with the wall 222 and 224. Further, the sheared flaps resiliently urge the sharp edges 330, 331, 332 and 333 against the curved walls 150 and 170 maintaining the good electrical connection with the covers 14 and 16.

Such an arrangement as provided and described with reference to the above figures, enables an embodiment of the invention to meet the requirements of BS EN 50085 1: 1999.

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Claims

1. An electrical trunking comprising a longitudinal base and at least a first and a second longitudinal cover and a resilient clip arranged to releasably retain both the first and the second covers to the base, the resilient clip providing electrical connection between the base and each of the covers, the resilient clip being retained to the base by means of a first set of teeth disposed longitudinally along two opposed edges of the clip, the base having an upstanding wall protruding between opposed legs of the clip, the upstanding wall arranged to maintain the engagement of the first set of teeth with the base, a second set of longitudinally disposed teeth on the clip, both sets of teeth being arranged to cut into the surfaces of the respective base or covers so as to establish the electrical connection.

2. An electrical trunking as claimed in claim 1, wherein one cover may removed from the base, leaving the other cover retained to the base.

3. An electrical trunking as claimed in claim 2, wherein a resistance of the electrical connection is less than 1/10 ohm.

4. An electrical trunking as claimed in claim 2, wherein the resistance of the electrical connection is less than 1/100 ohm.

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5. An electrical trunking as claimed in claim 2, wherein the resistance of the electrical connection is less than 1/iooo ohm.

6. An electrical trunking as claimed in any of the preceding claims, wherein the resilient clip has means arranged to provide high contact pressures with the cover and the base.

7. An electrical trunking as claimed in claim 6, wherein the means arranged to provide high contact pressures comprise resilient protrusions from the resilient clip.

8. An electrical trunking as claimed in claim 7, wherein the means arranged to provide high contact pressure further comprises sharp edges.

9. An electrical trunking as claimed in any of the preceding claims, wherein the cover and base are made of metal.

10. An electrical trunking as claimed in any one of claims 1 to 8, wherein the cover and base are made of a plastics material, which has an electrically conductive surface, on at least an inside surface of the trunking and including the connecting means of each of the base and the cover.

11. An electrical trunking substantially as hereinbefore described and with reference to the accompanying drawings.