AU2009202472A1

AU2009202472A1 - A Termination Gland For Shielded Electrical Cables

Info

Publication number: AU2009202472A1
Application number: AU2009202472A
Authority: AU
Inventors: Nicholas Edward Lackinger
Original assignee: TOLLARD HOLDINGS Ltd
Current assignee: CCG AUSTRALASIA Pty Ltd
Priority date: 2009-06-18
Filing date: 2009-06-18
Publication date: 2011-01-13
Also published as: AU2015261562A1; AU2017251825A1; AU2017251825B2

Description

P/00/011 28/5/91 Regulation 3.2 AUSTRALIA Patents Act 1990 ORIGINAL COMPLETE SPECIFICATION STANDARD PATENT Name of Applicant: Tollard Holdings Limited Actual Inventor Nicholas Edward Lackinger Address for service is: WRAYS Ground Floor, 56 Ord Street West Perth WA 6005 Attorney code: WR Invention Title: A Termination Gland For Shielded Electrical Cables The following statement is a full description of this invention, including the best method of performing it known to me: 1 2 A TERMINATION GLAND FOR SHIELDED ELECTRICAL CABLES FIELD OF THE INVENTION 5 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 sheath may be effectively electrically connected to a datum conductor for 10 maintaining a required potential in the electrically conductive shielding, typically a ground potential. In particular, but not necessarily exclusively, the invention relates to a termination gland for use in association with shielded electrical cables in 15 which the shielding is a copper or aluminium tape such as in EMC (electromagnetic compatibility) copper tape shielded cables. Clearly therefore the termination gland is also suitable for use on shielded electrical cables wherein the shielding is formed as a woven or braided layer of fine electrically conductive wires. 20 It is to be understood that the term shielded cables as used in this specification is intended to embrace all shielded or screened cables irrespective of the particular terminology used to describe them. 25 BACKGROUND TO THE INVENTION The electrically conductive shielding in shielded cables, particular copper or aluminium tape shielding such as the copper tape in EMC shielded cables, being rather thin, needs to be attached to an electrically conductive part of a 30 termination gland at a terminal end of the cable in a manner ensuring that electrical continuity between the shielding and the electrically conductive part of the gland remains intact during the life of the installation.

3 One 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 surfaces in view of the fact that a completely even clamping force 5 over the surface cannot, in practice, be achieved. The tape is rather thin and can tend to crumple rather easily with any high spots where a clamping force is maximum possibly becoming sites at which tears in the tape can initiate. Accordingly, it is not practical to use a pair of unyielding rigid clamping 10 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. Added to this is the danger that the copper or aluminium tape has sharp 15 edges that can tend to cut an installer's fingers if the tape needs to be unravelled from the inner cable sheath. 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 20 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 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 25 electrically insulating plastic sheath of the cable. Clamping is thus effected between a rigid but deformable surface and a deformable substantially less rigid plastic sheath. This solution is also accompanied by the requirement that suitable swaging apparatus needs to be made available at an installation site as and when such a cable is to be terminated. 30 4 Reference to cited material or information contained in the text should not be understood as a concession that the material or information was part of the common general knowledge or was known in Australia or any other country. 5 OBJECT OF THE INVENTION It is an object of this invention to provide a termination gland that provides an electrical connection with electrically conductive shielding that overcomes, at least to some extent, the difficulties that applicant perceives exist in respect 10 of the prior art solutions indicated above. SUMMARY OF THE INVENTION In accordance with this invention there is provided a termination gland 15 suitable for use on a shielded electrical cable, 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 sealing and gripper unit associated with 20 the entrance end for engaging the outer sheath of a cable, and an electrical contact assembly positioned between the entrance and exit ends of the body, the electrical contact assembly comprising an electrically conductive ring made of a helically wound electrically conductive wire whereof the axis of the helix follows the path of said ring so that the helix operatively encircles 25 exposed electrically conductive shielding of a cable and wherein the pitch of the helix is selected to enable the ring to be urged inwards to reduce its effective diameter, the electrical contact assembly further comprising two components each of which has a surface cooperating with the ring on opposite sides thereof to enable the ring to be urged inwards into contact 30 with said exposed electrically conductive shielding when the two components are urged towards each other.

5 Further features of the invention provide for the ring to be defined by a length of helically wound spring steel wire held to its ring-shape by resilient engagement thereof with an inner surface of one of said components in which instance the free ends of the helically wound spring steel wire may be 5 unconnected with each other; for said two components to be an inner body component and a cooperating compression nut; for each of the said two components to have an inclined generally truncated conical surface cooperating with the electrically conductive ring; for said two components to have co-operating screw threads thereon whereby the two components can 10 be moved relative to each other to effect urging of the electrically conductive ring inwards in use into contact with exposed electrically conductive shielding of a cable passing through the gland; and for an inner body component to be received in a main body component with a seal being provided to effectively seal between the outer surface of the inner body component and the inner 15 surface of the main body component. Still further features of the invention provide for the main body component to have the outer sealing and gripper unit at its entrance end; and for the outer sealing and gripper unit to comprise an elastomeric ring and cooperating 20 terminal nut having an inwardly directed flange at its entrance end whereby the elastomeric ring may be axially compressed to cause inward bulging of the elastomeric material into operatively firm contact with the outer sheath of a cable. 25 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. BRIEF DESCRIPTION OF THE DRAWINGS 30 In the drawings:- 6 Figure 1 is a partly sectioned perspective view of one embodiment of cable gland according to the invention; Figure 2 is a partly sectioned side elevation of the cable gland 5 illustrated in Figure 1 operatively installed on an electrical cable; Figure 3 is a cross-section taken through the cable at a position indicated by line Ill to Ill in Figure 2; and, 10 Figure 4 is an exploded and partly sectioned perspective view of the gland illustrated in Figure 1 illustrating schematically its various components (with screw threads not being illustrated). 15 DETAILED DESCRIPTION WITH REFERENCE TO THE DRAWINGS In the embodiment of the invention illustrated in the drawings, a termination gland, generally indicated by numeral (1), is suitable for use on a shielded 20 electrical cable (2) of the type having copper tape shielding (3) helically wound around an inner electrically insulating sheath (4) and covered by means of an outer electrically insulating sheath (5). The termination gland comprises a tubular main body component (6) having 25 an entrance end (7) for receiving the outer sheath of the electrical cable operatively passing through the gland and an exit end (8) for accommodating the inner sheath of the electrical cable operatively passing through the gland. The entrance end has an outer sealing and gripper unit (9) associated with it for engaging the outer sheath of the cable and physically locking the gland to 30 the outer sheath as well as sealing the entrance to the gland.

7 The outer sealing and gripper unit comprises, in this instance, an elastomeric ring (10) and cooperating terminal nut (11) having an inwardly directed flange at its entrance end whereby the elastomeric ring may be axially compressed to cause inward bulging of the elastomeric material into operatively firm 5 contact with the outer sheath of a cable. As provided by this invention, an electrical contact assembly (12) is positioned between the entrance and exit ends of the body, the electrical contact assembly comprising an electrically conductive ring (13) made of a 10 helically wound, electrically conductive spring steel wire whereof the axis of the helix is bent to follow the path of said ring so that the helix operatively encircles an exposed electrically conductive shielding of a cable passing through the gland. The pitch of the helix is selected to enable the electrically conductive ring to be urged inwards to reduce its effective diameter in order 15 to urge the ring into firm engagement with the copper tape shielding, in use. Such an electrically conductive ring may be made by making short straight lengths of helically wound spring steel wire and flexing the length of helically wound spring steel wire to assume the form of the ring with the ring shape being retained by cooperation with an internal shallow groove (14) (see 20 Figure 2) on the inside surface of an inner body component (15) that forms one of said two components that cooperate with the electrically conductive ring. It is, of course, also possible, although more costly, to join the free ends of the lengths of helically wound spring steel wire in any suitable manner. 25 The other of said two components is formed by a compression nut (16) each having a surface cooperating with the ring from opposite sides thereof to enable the ring to be urged inwards into contact with said exposed electrically conductive shielding. 30 In this embodiment of the invention these two components are an inner body component (15) and a cooperating compression nut (16) with these two components having screw threads, indicated by numeral (17) (see Figure 2), 8 whereby the compression nut can be screwed into the inner body component to effect urging of the electrically conductive ring inwards into operative contact with exposed electrically conducted shielding of a cable passing through the gland. Each of these two components has an inclined, truncated 5 conical surface (18) cooperating with the ring for this purpose. The truncated conical surface extends, in this instance, at about 450 to the axis of the cable gland. In the assembled condition of the cable gland, the inner body component (15) 10 is received partially in the main body component (6) with an O-ring type of seal (19) being provided to effectively seal between the outer surface of the inner body component and the inner surface of the main body component. The inner body component has, in the usual way, a coaxial externally screw 15 threaded tubular spigot (20) for connecting and sealing the gland to an electrical connection box or other anchorage therefor. In order to install the cable gland described above, the main body component and its associated sealing and gripper unit are removed from the inner body 20 component and slid along the cable. The outer insulating sheath is removed at the appropriate location and the copper tape shielding is cut off at a position spaced from the end of the outer insulating sheath by a distance approximately equal to the length of the assembly of the inner body component and the compression nut. The latter assembly is then introduced 25 over the exposed copper tape shielding preferably whilst rotating it in the direction in which the copper tape is wound in order not to disturb the copper tape. The compression nut is then tightened relative to the inner body component 30 in order to urge the electrically conductive ring somewhat radially inwards into firm electrical contact with the exposed copper tape shielding. The main body component is then screwed onto the inner body component; tightened; 9 followed by tightening of the sealing and gripper unit (9). At this stage the interior of the gland is fully sealed by the sealing and gripper unit on the one hand and the O-ring seal (19) acting between the inner body component and the main body component. 5 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 components whereby the electrically conductive ring is urged radially inwards can be varied widely, especially 10 according to the basic design of the cable gland. Throughout this specification, unless the context requires otherwise, the word "comprise" or variations such as "comprises" or "comprising", will be understood to imply the inclusion of a stateg integer or group of integers but 15 not the exclusion of any other integer or group of integers.

Claims

1. A termination gland suitable for use on a shielded electrical cable, the termination gland comprising a tubular body having an entrance end 5 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 sealing and gripper unit associated with the entrance end for engaging the outer sheath of a cable, and an electrical contact assembly 10 positioned between the entrance and exit ends of the body, the electrical contact assembly comprising an electrically conductive ring made of a helically wound electrically conductive wire whereof the axis of the helix follows the path of said ring so that the helix operatively encircles exposed electrically conductive shielding of a cable and 15 wherein the pitch of the helix is selected to enable the ring to be urged inwards to reduce its effective diameter, the electrical contact assembly further comprising two components each of which has a surface cooperating with the ring on opposite sides thereof to enable the ring to be urged inwards into contact with said exposed electrically 20 conductive shielding when the two components are urged towards each other.

2. A termination gland as claimed in claim 1 in which the ring is defined by a length of helically wound spring steel wire held to its ring-shape 25 by resilient engagement thereof with an inner surface of one of said components.

3. A termination gland as claimed in claim 2 in which the free ends of the helically wound spring steel wire are not connected to each other. 30 11

4. A termination gland as claimed in any one of the preceding claims in which said two components are an inner body component and a cooperating compression nut.

5 5. A termination gland as claimed in any one of the preceding claims in which each of the said two components has an inclined generally truncated conical surface cooperating with the electrically conductive ring. 10

6. A termination gland as claimed in any one of the preceding claims in which the said two components have inter-acting screw threads thereon whereby the two components can be moved relative to each other to effect urging of the electrically conductive ring inwards into operative contact with exposed electrically conductived shielding of a 15 cable passing through the gland.

7. A termination gland as claimed in any one of the preceding claims in which an inner body component is received in a main body component with a seal being provided to effectively seal between the outer 20 surface of the inner body component and the inner surface of the main body component.

8. A termination gland as claimed in any one of the preceding claims in which for the main body component has the outer sealing and gripper 25 unit at its entrance end.

9. A termination gland as claimed in any one of the preceding claims in which the outer sealing and gripper unit comprises an elastomeric ring and cooperating terminal nut having an inwardly directed flange at its 30 entrance end whereby the elastomeric ring may be axially compressed to cause inward bulging of the elastomeric material into operatively firm contact with the outer sheath of a cable. 12

10. A termination gland substantially as herein described and exemplified with reference to the accompanying drawings.