GB2269945A - Conductive grommet - Google Patents

Abstract

A conductive grommet (10) formed of rubber material is of generally annular form comprising an aperture through which a shielded cable is to be located in use. The rubber material which may be impregnated with carbon powder is provided with a number of strands forming a conductive member (14) within grommet (11). Member (14) may extend in a general S formation between surfaces (21) and (22). In use, the grommet (10) conducts electrical current between the shielded cable and an inner surface of a housing. <IMAGE>

Description

CONDUCTIVE GROMMET FIELD OF THE INVENTION The following invention relates to grommets, typically to be used for the sealing against moisture, dust etc. of industrial electrical cables.

Conventional grommets as used to seal industrial electrical cables from moisture are fabricated of neoprene nitrol or lead. Where a need may arise to conduct electricity through a grommet as for example when such a grommet is used in a lead shielded cable, lead and/or "conductive rubber" is employed. "Conductive rubber" is rubber adapted to conduct electricity therethrough as a result of it being impregnated with carbon powder for example.

OBJECT OF THE INVENTION It is the object of the present invention to substantially improve the electrical or mechanical properties of conductive grommet systems.

DISCLOSURE OF THE INVENTION There is disclosed herein a grommet adapted to conduct electrical current from a first surface thereof to a second surface thereof, the grommet having formed therein a conductive member or series of conductive elements extending at least partially between said first and second surfaces.

Preferably the conductive member is flexible so as to flex with distortion of the grommet in use, and so to maintain the seal and retain the electrical conductivity.

Preferably the grommet is of annular form comprising a central aperture through which a shielded cable for example may be received and further comprising an outer annular surface to engage an inner surface of a housing for example. The first and second surfaces may be the inner and outer annular surfaces. The grommet may further comprise a pair of annular end plates extending at least partially between the inner and outer surfaces in which case the conductive member or series of conductive elments may extend between either or both end plates and either or both annular surfaces.

In a preferred form of the invention the grommet is formed of non-conductive material such as neoprene. In this instance, the conductive member extends fully between said first and second surfaces.

Alternatively, the grommet may be formed of conductive material such as carbon impregnated neoprene. In this instance, the conductive member need not extend fully between said first and second surfaces.

Alternative application is for providing electrical continuity between the armouring of cables and the earthing/grounding surface, at the same time as providing mechanical sealing and support.

BRIEF DESCRIPTION OF THE DRAWINGS A preferred form of the present invention will now be described by way of example with reference to the accompanying drawings, wherein: Fig. 1 is a schematic end elevational view of a grommet, Fig. 2 is a schematic cross-section side elevational view taken at B-B of Fig. 1, Fig. 3 is a schematic exploded sectional view of detail C depicted in Fig. 2, Fig. 4 is a schematic cross-sectional view taken at A-A in Fig. 3, and Fig. 5 is a schematic cross-sectional elevational view of an exemplary application of a grommet to a mining plug.

DESCRIPTION OF THE PREFERRED EMBODIMENT In the accompanying drawings there is schematically depicted a grommet 10. Grommet 10 is typically formed of rubber material such as neoprene 11. Grommet 10 is of generally annular form comprising an aperture 20 through which-. a cable is to be located in use. On the inner annular surface 21 of grommet 10 a series of ridges 18 is provided. Ridges 18 serve to sealingly and electrically engage grommet 10 with a cable extending through aperture 20. At opposing sides of grommet 10 a pair of end plates 12 and 13 are provided. End plates 12 and 13, typically formed of steel or other metal are adapted to compress neoprene 11 in a direction indicated by arrows D by any means when located within an electrical housing for example. The outer diameter of end plates 12 and 13 is typically slightly smaller than that of grommet 10.

In the embodiment depicted, neoprene 11 may or may not be impregnated with carbon powder. For the purpose of providing a reliable electrical connection between inner surface 21 and outer surface 22 of grommet 10, a plurality of strands 15 forming a conductive member 14 is provided within grommet 10. In the embodiment depicted conductive member 14 extends in a general S formation between surfaces 21 and 22. Accordingly, conductive member 14 may flex during compression of neoprene 11 without breakage.

Individual strands 15 may form a mesh as depicted in Fig. 4. Strands 15 are typically formed of copper or other light conductive material. The type of material employed should ensure that grommet 10 retains its flexibility for sealing and gripping a cable. The mesh may be woven or non-woven.

It is envisaged that, when compared with the conductivity of a standard carbon impregnated grommet, the grommet disclosed herein may provide a three-fold increase in current flow, as a result of decreased electrical resistance.

Any arrangement of copper, or substitute, which has the effect of conducting electricity substantially through grommet 10 will suffice. Where conductive neoprene 11 is employed, the conductive nature of the same will complete conduction. It should be appreciated in this instance that member 14 need not extend fully between surfaces 21 and 22.

Where non-conductive rubber is employed in grommet 10, the member 14 should extend the full distance between inner and outer surfaces 21 and 22.

An exemplary application of grommet 10 is depicted in Fig. 5. In this instance, a mining plug 51 is depicted having a pair of conductive grommets 10 therein. The grommets 10 in this case provide continuity between the cable armour 50 through the end plates 12, 13 on the pair of grommets 10 and the body 51 of the plug.

It should be appreciated that modifications and alterations obvious to those skilled in the art are not to be considered as beyond the scope of the present invention. For example, rather than the provision of a mesh conductive member 14, a rigid or flexible radially orientated member may extend partially between inner and outer surfaces 21 and 22. That is, where conductive member 14 need not extend fully between surfaces 21 and 22, the member need not be flexible. Furthermore, two or more members 14 may be provided in a single grommet 10.

Claims (7)

1. A grommet adapted to conduct electrical current from a first surface thereof to a second surface thereof, the grommet having formed therein a conductive member or series of conductive elements extending at least partially between said first and second surfaces.

2. A grommet as claimed in claim 1 wherein the conductive member is flexible so as to flex with distortion of the grommet in use.

3. A grommet as claimed in either preceding claim being of annular form comprising a central aperture through which a shielded cable for example may be received and further comprising an outer annular surface to engage an inner surface of a housing for example.

4. A grommet as claimed in claim 3 further comprising a pair of annular end plates extending at least partially between the inner and outer annular surfaces.

5. A grommet as claimed in any preceding claim, being formed of non-conductive material and comprising a conductive member extending fully between said first and second surfaces.

6. A grommet as claimed in any one of claims 1 to 4 being formed of carbon impregnated neoprene.

7. A grommet substantially as hereinbefore described with reference to the accompanying drawings.