GB2280317A

GB2280317A - Cable glands

Info

Publication number: GB2280317A
Application number: GB9315032A
Authority: GB
Inventors: Anthony James Gray; John Alexander Walton
Original assignee: PEPPERS CABLE GLANDS Ltd
Current assignee: PEPPERS CABLE GLANDS Ltd
Priority date: 1993-07-20
Filing date: 1993-07-20
Publication date: 1995-01-25
Anticipated expiration: 2013-07-20
Also published as: GB9315032D0; GB2280317B

Abstract

The annular seal (50) of a cable gland is formed of conductive rubber. <IMAGE>

Description

CABLE GLANDS This invention relates to cable glands.

A cable gland comprises a tubular body which forms a through passage for a cable and which comprises two inter-engagable parts which co-operate when inter-engaged to form an annular recess in the through passage, the annular recess comprising accommodation for an annular seal of deformable material, the two inter-engagable parts being adapted when inter-engaged to clamp the annular seal between them and to apply pressure to the annular seal whereby to cause the latter to be deformed and to be urged into sealing engagement with and around a cable which is lead through the through passage.

In certain installations, when the cable gland is fitted to a cable having a metal sheath (for example, a lead sheath), there is a requirement for electrical continuity to be established within the cable gland and structure within which it is mounted when the cable gland is assembled with its sealing ring in sealing engagement with the metal sheath substantially circumferentially continuously around the metal sheath. To that end, it is customary to use an annular seal either of a deformable metal such as lead or to use a small piece of deformable metal backed up by an elastomeric seal. However, the first of these seals has the disadvantage that it has to be tailor made to suit the diameter of the metal sheath. On the other hand, the second of these seals employs an additional, usually complex, metal part in the gland.

It is usually effected by having a thin metal part compressed on to the sheath by the elastomeric part, which also acts as a seal.

For other installations, the cable is provided with a screen which comprises an aluminium foil layer sandwiched between sleeves of plastics material. The latter are provided for weather-proofing purposes whilst the aluminium foil screen is provided to protect the conductors from the effects of electromagnetic fields through which the cable may be lead, or which may arise due to the effects of such things as lightning or a powerful electric motor. If such a cable is a telecommunications cable which must be passed close to a high power cable because of space limitations, such as may arise in an underwater tunnel, the forces acting on the telecouuunications cable due to the electromagnetic field are liable to be so large as to cause serious eddy current effects in the cores of the communications cable, which will interfere with the transmitted data. It is necessary under normal electromagnetic protection practice to earth the screen with a 3600 connection.

According to this invention there is provided a cable gland comprising a tubular body which forms a through passage for a cable and which comprises two inter-engagable parts which co-operate when inter-engaged to form an annular recess in the through passage, the annular recess providing accommodation for a seal of deformable material, the two inter-engagable parts being adapted when inter-engaged to clamp the annular seal between them and to apply pressure to the annular seal whereby to cause the latter to be deformed to be urged into sealing engagement with and around a cable which is lead through the through passage, wherein the annular seal of deformable material is formed of a conductive elastomeric material.

The following is a description, by way of example only of a method of carrying the invention into effect.

Figure 1 is an exploded view, partly in section, of a cable gland accommodating a cable 10.

A gland body 60 includes a substantially cylindrical portion 62 which is provided with an external thread 68. The portion 62 is screwed into a tapped hole in the wall of an enclosure (not shown). (Alternatively, the cylindrical portion 62 may have a clearance fit in the hole and in this case the body 60 may be secured by a retaining nut on the opposite side of the wall.) A stepped axial bore 66 extends through the gland body 60, allowing the cable 10 to pass through. The bore 66 includes a bore portion 67 which extends through the threaded cylindrical portion 62 and through a juxtaposed nut portion 63 of substantially hexagonal cross-section. The bore widens into a bore portion 65 which is coaxial with the bore portion 67, and which accommodates an annular inner seal 50 of conductive rubber, through which the cable 10 passes. The inner seal 50 is located on a shoulder 70 at the interface of bore portions 65 and 67, and the external diameter of the seal 50 is such that it fits snugly into the bore portion 65. The diameter of the bore of the seal 50 when it is in its natural relaxed state is substantially the same as the diameter of bore portion 67. When in this uncompressed state, the seal 50 extends axially beyond the bore portion 65, part way into a further axial bore portion 64 of larger diameter.

Bore portions 64 and 65 together form the interior of another substantially cylindrical portion 61, which is separated from cylindrical portion 62 by the nut portion 63, and which is provided with an exterior thread 69. Cylindrical portion 61 is of a larger external diameter than cylindrical portion 62, but they are coaxial with each other and with nut portion 63.

The exterior of the inner seal 50 is provided with a V shaped circumferential groove 51 which allows greater axial compression of the seal 50 without discouraging the associated inward bulging. On assembly a thin plastic annular skid-washer with an aperture 41 of the same diameter as the bore portion 67 is placed between the seal 50 and a cylindrical bush 30 with an axial bore 33 of the same diameter as that of the bore portion 67. Cylindrical bush 30 has a stepped external diameter: a bush portion 34 is of such a diameter that it fits snugly into bore portion 64 of gland body 60, but will not fit into the smaller-diameter bore portion 65. A bush portion 35 has a larger diameter than bush portion 34, and fits snugly into a bore 22 of a substantially cylindrical gland cap 20 of hexagonal cross-sectional perimeter.

Bore 22 is provided with an internal flange 23 at that end of the bore 22 which is remote from the gland body 60. The gland cap 20 is fitted over the bush 30, washer 40, seal 50 and gland body 60, and an internal thread 21 of the bore 22 engages the external thread 69 of cylindrical gland body portion 61.

As the cap 20 is tightened by rotation against the gland body nut portion 63, the internal flange 23, is brought into abutment with bush portion 35.

The separate components of the gland may be threaded onto the cable 10 in the correct order before assembly, or alternatively the gland may be assembled (but not tightened) and subsequently threaded onto the cable 10.

Tightening of the gland cap 20 forces bush portion 34 against one side of the skid washer 40, compressing the seal 50 which abuts shoulder 70 of gland body 60.

The bush portion 34 and washer 40 are in slidable contact, so that any rotation of the bush 30 due to tightening of the cap 20 is not transmitted to the inner seal 50. This ensures that the seal 50 is not deformed in an undesirable way, and makes firm tightening easier to achieve. The rubber seal, on compression, bulges inwardly, and the internal bore of the seal 50 narrows sufficiently to clamp the cable 10 firmly in place, without leaving any gaps between the outer sheath of the cable and the inner seal 50.

The seal is thus fluid-tight and will therefore prevent, for example, the ingress of potentially explosive gas to the enclosure, which will typically contain electrical apparatus capable of igniting an explosive gas mixture.

In contrast to previously known lead seals, which required a close match between the diameter of the cable and that of the seal bore, the elastomeric nature of the conducted rubber seal allows for a far wider range of cable diameters to be accommodated by a given size of seal. This need to match cable and seal diameters is thus avoided saving time in assembly.

Since the seal is electrically conductive, it can also be used in applications where it is necessary not only to clamp and seal the cable, but also to earth an electrically conducting cable sheath. Such an application might be where EMC grounding is required, in order to electromagnetically shield the cable, this will typically involve stripping away a short length of the non-conductive outer sheath of the cable to reveal the conducting cable sheath, and then arranging the cable gland so that the seal clamps the exposed portion providing intimate 3600 electrical grounding around the cable, as well as a fluid tight seal. The seal is grounded via the cable gland body and either the enclosed wall, or a grounding plate onto which the gland is mounted. In this way, the electrical continuity required by BS 6121 may be maintained.

Claims

CLAIMS:

1. A cable gland comprising a tubular body which forms a through passage for a cable and which comprises two inter-engageable parts co-operate when inter-engaged to form an annular recess in the through passage, the annular recess providing accomodation for a seal of deformable material, the two inter-engageable parts being adapted when inter-engaged to clamp the annular seal between them and to apply pressure to the annular seal whereby to cause the latter to be deformed to be urged into sealing engagement with and around a cable which is lead through the through passage, wherein the annular seal of deformable material is formed of a conductive elastomeric material.

2. A cable gland according to claim 1, wherein said two inter-engageable parts comprise a tubular gland body which has a stepped bore and an exterior screw thread, and an annular gland cap which is screwed onto the exterior thread and which has an internal annular flange, there being an annular bush which reacts against the internal flange, and an annular skid washer between the bush and a step of the stepped bore, the annular seal being between the annular skid washer and the step and being deformed radially inwardly into contact with a cable lead through the cable gland by being clamped between the step and the skid washer by the action of screwing the annular gland cap onto the exterior thread of the tubular gland body.

3. A cable gland according to claim 2, wherein the exterior of the annular seal is provided with a V-shaped circumferential groove which allows axial compression of the seal without discouraging inward bulging.

4. A cable gland according to any one of claims 1 to 3, which is fitted to a cable having a metal sheath, the annular seal being substantially circumferentially continuously engaged with the metal sheath.

5. A cable gland according to any one of claims 1 to 3, which is fitted to a cable which is provided with a metal screen sandwiched between sleeves of plastics material, the outer one of the sleeves of plastics material being stripped away so that the annular seal is clamped onto the metal screen whereby to provide an earth connection for that screen.

6. A cable gland substantially as described hereinbefore with reference to and as illustrated in the accompanying drawing.