AU2007231850B2 - Termination Gland for a Shielded Electrical Cable - Google Patents

Description

TERMINATION GLAND FOR A SHIELDED ELECTRICAL CABLE 5 FIELD OF THE INVENTION This invention relates to a termination gland that is especially suitable for a shielded electrical cable whereby the electrically conductive shielding that is generally sandwiched between an inner and an outer electrically insulating 10 sheath may be effectively electrically connected to a datum conductor for maintaining a required potential in the electrically conductive shielding, typically a ground potential. In particular, but not necessarily exclusively, the invention relates to a 15 termination gland for use in association with shielded electrical cables in which the shielding is a copper or aluminium tape such as in EMC (electromagnetic compatibility) copper tape shielded cables. BACKGROUND TO THE INVENTION 20 The electrically conductive shielding in shielded cables, particular copper tape shielding in EMC shielded cables, being rather thin, needs to be attached to an electrically conductive part of a termination gland at a terminal end of the cable in a manner ensuring that electrical continuity between the 25 shielding and the electrically conductive part of the gland remains intact during the life of the installation. The difficulty is that the physical strength of the copper tape may be seriously impaired if the tape is simply clamped firmly between a pair of rigid clamping 30 surfaces in view of the fact that a completely even clamping force over the surface cannot, in practice, be achieved. Any high spots where the clamping force is maximum can become a site at which a tear in the tape can initiate.

2 Accordingly, it is not practical to use a pair of unyielding rigid clamping surfaces such as the cone and clamping ring of an armour clamp that is used to terminate the multitude of rather rigid armour wires of an armoured electrical cable. 5 One solution to this problem has been to swage a deformable metal, typically lead, ring radially inwards onto the copper tape at a position where the outer insulating sheath of the cable has been removed to expose the copper tape shielding towards an end of the cable to be terminated. The problem with 10 this solution, as far as applicant is concerned, is that the force with which the deformable metal ring is swaged onto the copper tape is only met by resistance on the inside of the copper tape of the very deformable inner electrically insulating plastic sheath of the cable. Clamping is thus effective between a rigid but deformable surface and a deformable substantially less 15 rigid plastic sheath. This solution is also accompanied by the requirement that suitable swaging apparatus is available at the relevant site as and when such a cable is to be terminated. Of course, it is also important that longitudinal movement of the cable relative 20 to the electrical connection within the termination gland be prevented in so far as is possible in order for the electrical connection to maintain its integrity. The preceding discussion of the background to the invention is intended only to facilitate an understanding of the present invention. It should be 25 appreciated that the discussion is not an acknowledgment or admission that any of the material referred to was part of the common general knowledge as at the priority date of the application.

3 OBJECT OF THE INVENTION It is an object of this invention to provide a termination gland that provides an electrical connection with the electrically conductive shielding that has 5 enhanced reliability when compared to the prior art solution indicated above. SUMMARY OF THE INVENTION In accordance with this invention there is provided a termination gland 10 suitable for use on a shielded electrical cable having an outer sheath and an inner sheath, the termination gland comprising a tubular body having an entrance end for receiving the outer sheath of an electrical cable operatively passing through the gland and an exit end for accommodating the inner sheath of an electrical cable operatively passing through the gland, an outer 15 gripper unit associated with the entrance end for engaging the outer sheath of the electrical cable to inhibit longitudinal movement thereof relative to the entrance end, an inner gripper unit for engaging the inner sheath of the electrical cable to inhibit longitudinal movement thereof relative to the exit end of the body, and an electrical contact assembly positioned between the 20 entrance and exit ends of the body, the electrical contact assembly comprising an inner rigid tubular clamping member and an outer clamping ring wherein the tubular clamping member is adapted to encircle the inner sheath of the electrical cable operatively passing through the gland, the tubular clamping member having an outer clamping surface tapering towards 25 a free end that is directed towards the entrance end of the body, the clamping ring being adapted to cooperate with the outer clamping surface to operatively clamp electrically conductive shielding therebetween, the clamping ring having at least an inner surface region that is formed of a rigidly deformable electrically conductive material, and clamping means for 30 urging the clamping ring and tubular clamping member towards each other to operatively grip electrically conductive shielding therebetween.

4 Further features of the invention provide for the body to be composed of a central tubular part having the outer gripper unit associated one end thereof and the inner gripper unit associated with the other end thereof; for the outer gripper unit to comprise an elastomeric gripper / sealing ring and cooperating 5 nut having an inwardly directed flange at its entrance end whereby the elastomeric gripper ring may be axially compressed to cause inward bulging of the elastomeric material into operatively firm contact with the outer sheath of the electrical cable; for the inner gripper unit to comprise an elastomeric gripper / sealing ring and cooperating externally screw threaded sleeve 10 whereby the elastomeric gripper ring may be axially compressed to cause inward bulging of the elastomeric material into operatively firm contact with the inner sheath of the electrical cable; for the tubular clamping member to be interposed between the elastomeric gripper ring of the inner gripper unit and the clamping ring that is seated against a shoulder within the central 15 tubular part such that clamping force on the tubular clamping member is by way of the elastomeric gripper ring of the inner gripper unit; and for the clamping means to be screw threaded clamping means, in particular said externally screw threaded sleeve for urging the tubular clamping member and clamping ring towards each other by way of the inner elastomeric gripper ring 20 that is interposed therebetween. The clamping ring is conveniently made of lead or a suitable lead alloy of sufficient thickness to provide adequate strength to the ring whilst providing the requisite deformable surface that operatively contacts the electrically 25 conductive shielding of the electrical cable and deforms to accommodate high spots in the outer surface of the shielding. Alternatively, the lead or deformable alloy may be somewhat thinner and supported by an outer rigid metal ring, typically of brass. 30 In order that the above and other features of the invention may be more fully understood one embodiment thereof will now be described with reference to the accompanying drawings.

5 BRIEF DESCRIPTION OF THE DRAWINGS In the drawings: 5 Figure 1 is an elevation of one embodiment of termination gland according to an embodiment of the invention in an installed condition on an EMC shielded cable with the upper half shown in section; and, 10 Figure 2 is an end view thereof taken from the entrance end (right hand side) of the embodiment illustrated in Figure 1. DETAILED DESCRIPTION WITH REFERENCE TO THE DRAWINGS 15 In the embodiment of the invention illustrated in the drawings, a termination gland, generally indicated by numeral (1), is provided for a shielded EMC electrical cable (2) of the type having an electrical shield in the form of thin helically wound copper tapes (3). 20 The termination gland has a tubular body comprising a central tubular part (4) having, at an entrance end, an outer gripper unit (5) for engaging the outer sheath (6) of the cable to inhibit longitudinal movement thereof relative to the gland as well as serving purpose of an outlet seal. The outer gripper unit 25 comprises a suitable elastomeric gripper / sealing ring (7) and cooperating nut (8) having an inwardly directed flange (9) at its entrance end whereby the elastomeric gripper ring may be axially compressed to cause inward bulging of the elastomeric material into operatively firm contact with the outer sheath of the cable in well known manner. The gripper unit thus also operates also 30 as an outer seal in the manner of the well-known outer compression seal.

6 The central tubular part of the body has, at its other end, the exit end, an inner gripper unit (10) for engaging the inner sheath (11) of a cable to inhibit longitudinal movement thereof relative to the exit end of the body. The inner gripper unit likewise comprises a suitable elastomeric gripper / sealing ring 5 (12) that, in this instance, is located for compression axially between an inwardly directed shoulder (13) of an externally screw threaded sleeve (14) that extends into a cooperating screw threaded bore (15) in the central tubular part of the body at one end, and an axially movable rigid tubular clamping member (16) at the other end. The inner elastomeric gripper ring 10 may thus be axially compressed to cause inward bulging of the elastomeric material into operatively firm contact with the inner sheath of the cable. Located at the inner end of the internally screw threaded bore (15) is a shoulder against which a slip ring (17) bears, in use, and that axially supports 15 a lead clamping ring (18). The tubular clamping member (16) is adapted to closely encircle the inner sheath of the cable and has an outer clamping surface (19) tapering towards a free end (20) that is directed towards the entrance end of the body. The 20 arrangement is such that tubular clamping member has a relatively thin wall over the portion corresponding to the outer tapered clamping surface which has a very small angle of taper, typically less than about 5 degrees relative to the axis, and preferably about 3 or 4 degrees. 25 The clamping ring is adapted to cooperate with the outer clamping surface to clamp electrically conductive shielding, in this instance, the copper tape (3), therebetween. It will be understood that in this arrangement the externally screw threaded sleeve and cooperating internal screw thread of the central part of the body constitute screw threaded means for urging the outer 30 clamping surface of the tubular clamping member into the clamping ring to operatively grip the electrically conductive copper tape therebetween. Simultaneously, the inner gripper unit is rendered operative.

7 It will thus be understood also that the tubular clamping member is urged into its operative position by way of the elastomeric inner gripper ring of the inner gripper unit. 5 It will be understood that, in use, the deformability of the lead at the contact surface of the clamping ring will accommodate any high spots undulations in the outer surface of the shielding whilst the shielding remains properly supported on its inner surface by the rigid tubular clamping member where it 10 becomes interposed between the shielding an inner sheath. It will be understood that numerous variations may be made to the embodiment of the invention described above without departing from the scope hereof. In particular, the lead ring may be appreciably thinner and 15 radially supported on its outside by an outer rigid metal ring, typically of brass. Also, lead may be replaced by any other suitable rigidly deformable electrically conductive material. Throughout the specification, unless the context requires otherwise, the word 20 "comprise" or variations such as "comprises" or "comprising", will be understood to imply the inclusion of a stated integer or group of integers but not the exclusion of any other integer or group of integers. 25

Claims (10)

1. A termination gland suitable for use on a shielded electrical cable having an outer sheath and an inner sheath, the termination gland 5 comprising a tubular body having an entrance end for receiving the outer sheath of an electrical cable operatively passing through the gland and an exit end for accommodating the inner sheath of an electrical cable operatively passing through the gland, an outer gripper unit associated with the entrance end for engaging the outer sheath of 10 the electrical cable to inhibit longitudinal movement thereof relative to the entrance end, an inner gripper unit for engaging the inner sheath of the electrical cable to inhibit longitudinal movement thereof relative to the exit end of the body, and an electrical contact assembly positioned between the entrance and exit ends of the body, the 15 electrical contact assembly comprising an inner rigid tubular clamping member and an outer clamping ring wherein the tubular clamping member is adapted to encircle the inner sheath of the electrical cable operatively passing through the gland, the tubular clamping member having an outer clamping surface tapering towards a free end that is 20 directed towards the entrance end of the body, the clamping ring being adapted to cooperate with the outer clamping surface to operatively clamp electrically conductive shielding therebetween, the clamping ring having at least an inner surface region that is formed of a rigidly deformable electrically conductive material, and clamping means for 25 urging the clamping ring and tubular clamping member towards each other to operatively grip electrically conductive shielding therebetween.

2. The termination gland as claimed in claim 1 in which the body is 30 composed of a central tubular part having the outer gripper unit associated with one end thereof and the inner gripper unit associated with the other end thereof. 9

3. The termination gland as claimed in either one of claims 1 or 2 in which the outer gripper unit comprises an elastomeric gripper / sealing ring and cooperating nut having an inwardly directed flange at its 5 entrance end whereby the elastomeric gripper ring may be axially compressed to cause inward bulging of the elastomeric material into operatively firm contact with the outer sheath of the electrical cable.

4. The termination gland as claimed in any one of the preceding claims in 10 which the inner gripper unit comprises an elastomeric gripper / sealing ring and cooperating externally screw threaded sleeve whereby the elastomeric gripper ring may be axially compressed to cause inward bulging of the elastomeric material into operatively firm contact with the inner sheath of the electrical cable. 15

5. The termination gland as claimed in any one of the preceding claims in which the tubular clamping member is interposed between the elastomeric gripper ring of the inner gripper unit and the clamping ring that is seated against a shoulder within the central tubular part such 20 that clamping force on the tubular clamping member is by way of the elastomeric gripper ring of the inner gripper unit.

6. The termination gland as claimed in any one of the preceding claims in which for the clamping means is a screw threaded clamping means. 25

7. The termination gland as claimed in claim 6 in which the screw threaded clamping means comprises an externally screw threaded sleeve for urging the tubular clamping member and clamping ring towards each other by way of the inner elastomeric gripper ring that is 30 interposed therebetween. 10

8. The termination gland as claimed in any one of the preceding claims in which the clamping ring is made of lead or a suitable lead alloy providing a deformable surface that operatively contacts the electrically conductive shielding of the electrical cable and deforms to 5 accommodate high spots in the outer surface of the shielding.

9. The termination gland as claimed in claim 8 in which the clamping ring is supported by an outer rigid metal ring.

10 10. The termination gland substantially as herein described and exemplified with reference to the accompanying drawings. 15 20 25 30