GB2450519A

GB2450519A - A cable gland

Info

Publication number: GB2450519A
Application number: GB0712516A
Authority: GB
Inventors: Garry Pitchford; Stephen Bryan Walters
Original assignee: GLOBAL EMC SOLUTIONS Ltd; PRO TERM Ltd
Current assignee: PRO-TERM LIMITED
Priority date: 2007-06-28
Filing date: 2007-06-28
Publication date: 2008-12-31
Also published as: GB0712516D0

Abstract

A cable gland assembly (100) comprising: an electrically conductive body (111) having an engagement feature (125), an external threaded section (121) and an external contact surface (116) adapted to connect to a sheath of a cable passing through the cable gland; and an electrically insulating housing (112) adapted to directly engage with the engagement feature, the body and housing being adapted to clamp to first (123) and second (124) opposing surfaces of a wall (119) through a hole in the wall sized to receive the external threaded section of the body, wherein the engagement feature is adapted to secure the housing to the first surface of the wall.

Description

CABLE GLANDS

Field of the Invention

The invention relates to cable glands, and in particular to cable glands having a combination of electrically conductive and electrically insulating properties.

Background

Cable glands are used in many different indoor and outdoor applications, and in a variety of industrial and domestic applications including industrial systems, processes and product lines, electrical appliances, 1ihting, heating, ventilation, control and instrumentation, to name a few. In general, cable glands serve to terminate and/or mechanically fix a cable to an opening in a wall, enclosure, bulkhead or the like to prevent damage to the cable and to provide strain relief.

Cable glands may additionally provide an electrical termination for the cable, for example via connection to au electrically conductive sheath on a cable. Such electrical termmation can provide a connection for electromagnetic shielding of the cable. Environmental protection may also be afforded by certain types of cable glands, for example to protect against fluid ingress, in particular for terminations where an internal device is required to be protected from an external environment.

One function of cable glands is typically to offer cable retention by means of mechanically anchoring a protective armour or braid of the cable. This retention can offer electrical and/or mechanical security to the cable.

Typical types of currently available cable glands tend to fall within two main groups. Both types include a central cylindrical hollow body portion having external threaded portions either side of a central portion, being for example in the form of a hexagonal nut. A cable passing through the gland can be held in place via a separate clamping nut over one threaded portion, while the other threaded portion serves to secure the gland to a wall or bulkhead via a second nut. The cable gland can be configured to clamp mechanically on to the cable upon tightening of the clamping nut. The cable gland may alternatively (or additionally) be configured to clamp on to an exposed portion of the cable sheath to provide electrical connection to the cable gland.

In a first group, the hollow body portion and associated nuts are metal, and therefore electrically conductive. These parts can be made via casting and subsequent machining operations to provide the threaded portions. Electrical and mechanical terminations can he made simultaneously, for example by means of a clamping ring and cone arrangement for securing an external cable sheath. Such cable gland assemblies tend to be used in severe environments, such as in mining, 1 0 where the metal construction aids the robustness of the cable termination.

In a second group, the hollow body portion and most or all of the associated nuts are made from moulded polymeric materials such as thermoplastics. This allows the cable glands to be made much more cheaply than the equivalent metal 1 5 components. Moulded polymeric materials are not, however, good electrical conductors and cannot therefore provide electrical as w'ell as mechanical terminations. Further components such as earthing tags are commonly used to make electrical contact with an external cable sheath.

GB 2377829 provides an example of a cable gland falling within the first group, in which the cable gland has an armour clamp assembly comprising a cone and cooperating clamping ring. A body part having external threaded portions provides mechanical and electrical connection for a cable to an electrical connection box or other housing.

US 5589663 discloses an earthed cable gland of a type falling within the second group, in which the cable gland comprises a plastic hollow body portion with external threaded portions. An electrical connection is made with an external sheath of a cable passing through the gland via an earthing tag having resilient fingers situated over one of the threaded portions. Mechanical connection to the cable is made by means of a compressible elastomeric ring and nut, the compressible nng holding the components in position on tightening of the nut. A metallic frusto-conical hollow cylinder is positioned inside to provide an electrical connection to an exposed length of armour of the cable.

Previous solutions, as evidenced by cable glands of the above described types, tend either to be either expensive, due to being made from several cast and/or machined metal components. and/or complicated, due to the need for additional components to achieve electrical as well as mechanical connections. Some metal cable glands also afford environmental protection and electrical continuity via seals, but this option is often through a complicated and more expensive arrangement.

There is a need for terminating protected cables into joint boxes, electrical distribution panels, electrical equipment, electrical panels, control panels/boxes, motors and many other applications where the expense of an all-metal construction might not be justifiable. For such applications, polymeric cable glands offer environmental protection and corrosion resistance but do not offer 1 5 electrical continuity or cable armour/braid retention features.

It is therefore an object of the invention to address one or more of the above mentioned problems.

Summary of the invention

In a first aspect, the invention provides a cable gland assembly comprising: an electrically conductive body having an engagement feature, an external threaded section and an external contact surface adapted to connect to a sheath of a cable passing through the cable gland; and an electrically insulating housing adapted to directly engage with the engagement feature, the body and housing being adapted to clamp to first and second opposing surfaces of a wall through a hole in the wall sized to receive the external threaded section of the body, wherein the engagement feature is adapted to secure the housing to the first surface of the wall.

In a second aspect, the invention provides a cable gland assembly comprising: an electrically conductive body having an external threaded section and an external contact surface adapted to connect to a sheath of a cable passing through the cable gland; and an electrically insulating housing adapted to direct]y engage with the engagement feature, the body and housing being adapted to clamp to first and second opposing surfaces of a wall through a hole in the wall sized to receive the external threaded section of the body, wherein the external threaded section is adapted to engage with an internal threaded section of the housing to secure the housing to the first surface of the wall.

In a third aspect, the invention provides a cable gland assembly comprising: a metal part adapted to pass through a wall hole, the metal part having a cable sheath contact surface and means for engagement with a first surface of the wall; a plastic part adapted to provide opposing means for engagement with a second opposing surface of the wall and means for engagement with the metal part.

In certain aspects, the invention provides for a cable gland allowing electrical and mechanical connection to be made to a cable with a reduced number of components, through the use of both electrically conductive and electrically insulating parts.

Detailed Description

The invention will now be described by way of example, and with reference to the accompanying drawings in which: figure 1 shows a partial cross-sectional view of an exemplary cable gland assembly in an assembled configuration; figure 2 shows a partial cross-sectional view of an alternative exemplary cable gland assembly in an assembled configuration; figure 3 shows a partial cross-sectional view of modification to the alternative cable gland assembly of figure 2; figure 4 shows a partial cross-sectional view of a further alternative exemplary cable gland assembly in an assembled configuration; figure 5 shows a partial cross-sectional view of a modification to the further alternative cable gland assembly of figure 4; figure 6 shows a schematic exploded view of various components of a further exemplary cable gland assembly; and figure 7 shows a schematic view of the cable gland assembly of figure 6 in an assembled configuration.

An illustration of a preferred exemplary embodiment is shown in figure 1. In this drawing, the upper portion shows a section through the cable gland assembly 100, while the lower portion shows a side view of the outer appearance of the assembly. A central passage 122 for accommodating a suitable diameter of cable runs through the assembly. It is to be understood from the drawings that the cable glands in general have rotational symmetry about the longitudinal axis of the assembly.

The assembly 100 comprises an electrically conductive body 111 and an electrically non-conductive housing 112. The housing 112 and body 111 are secured to first 123 and second 124 opposing surfaces respectively of a wall 119 via a hole in the wall, the hole being sized to receive a threaded section 121 of the body Ill. In the embodiment shown, a locknut 113 is engaged with the threaded section 121 of the body 111. A face 120 of the locknut 113 engages with the second surface 124 of the wall 119.

The body 111 comprises an engagement feature in the form of an external radially extending flanged portion 125. The flanged portion 125 engages with a corresponding internal radially extending flanged portion 126 on the housing 112 so that a face 127 of the housing engages with the first surface 123 of the wall 119 when the locknut 113 is tightened on to the body Ill. To avoid rotation of the housing 112 relative to the body 111 when the locknut 113 is being tightened, the flanged portion 125 of the body ill is preferably non-circular and shaped to fit into a correspondingly shaped recess in the housing 112, for example in the form of a hexagonal shoulder fitting into a corresponding hexagonal recess in the housing 112.

The face 1 20 of the locknut 113 is preferably adapted such that, when threaded on the body 111 and forced against the second surface 124 of the wall 11 9, the surface 124 is abraded or mechanically keyed to form an electrical connection between the wall 119 and the body 111. The waIl 119 may, for instance, have an insulating surface layer such as oxide or paint which will need to be broken through in order to achieve a good electrical connection. Adapting the surface 120 of the locknut 113 by knurling, abrading or otherwise machining can be employed for this purpose. Such a connection is important when, for example, an earthed connection to an external sheath of a cable is required for safety and/or electromagnetic shielding purposes.

To ensure a connection is made against hard surfaces such as steel, the face 120 of the locknut, or other component coming into contact with the second surface 124 of the wall 119, can be hardened such as by a case hardening process or by deposition of a harder material. For example, an electroplated nickel coating can be used to raise the surface hardness to around 50 Rockwell, compared with around 30 Rockwell for mild steel.

The contact surface 116 of the body Ill is, in this particular embodiment, in the form of a conical shape, around which a part of an external sheath or armour of a cable can be placed. An electrically insulating pusher body 114 engages with the housing 112, forcing an electrically conductive sheath contact ring 117 on to the cable sheath placed between the ring 117 and the electrically conducting contact surface 116. Threaded sections 128 on the housing 112 and the pusher body 114 allow the pusher body 114 to be tightened on to the housing 112 and thereby clamping and mechanically securing the cable sheath to the body 111. This provides a secure mechanical connection as well as an electrical connection between the cable sheath and the body 111, and can be seen in more detail in figure 4, described below.

A seal pusher 115 engages with the pusher body 114 by means of threaded sections 129 on the seal pusher 115 and the pusher body 114 to compress a sealing ring 118 around the, cable. The sealing ring 118 is made from a compressible material such that compression by engagement of the seal pusher ii 5 with the pusher body 114 causes the internal diameter of the sealing ring to reduce and thereby clamp on to the outer surface of the cable. This provides a mechanical connection to the outer protective sheath of the cable as well as an environmental seal to prevent fluid ingress around the cable.

Figure 2 illustrates an alternative cable gland assembly, in which the body 211 and housing 220 are engaged together by means of corresponding threaded sections 221, 222 on the body 211 and housing 212 respectively. The threaded sections 221, 222 are adapted to engage with each other to secure the housing 212 to the first surface 123 of the wall 119. A flanged portion 225 of the body clamps directly on to the second surface 124 of the wall 119 via a surface 220 of the flanged portion 225. The surface 220, similarly to the locknut 113 of figure 1, may be abraded or otherwise mechanically keyed to form an electrical connection with the wall 119. The threaded sections 221, 222 are adapted to engage with each other to secure the housing 212 to the first surface 123 of the wall 119.

Also shown in figure 2, the pusher body 214 has within it a captive sheath contact ring 217, the ring 217 being captive to the pusher body 214 by means of an engagement feature 219, for example comprising tapered and stepped surfaces which mate together through an interference fit between the ring 217 and the pusher body 214. The ring 217 is preferably free to rotate within the pusher body 214 when fitted and before being engaged with the cable sheath upon assembly of the cable gland. The remaining features of the assembly, being the seal pusher 215 and sealing ring 218, operate in a similar way as described above in relation to figure 1.

Figure 3 illustrates a modified version of the cable gland assembly of figure 2, in which the sheath contact surface 316 of the body 311 and the sheath contact ring 3 17 are configured to mate together to provide a more secure mechanical connection to a cable sheath positioned between the components. Ribs 3 1 9a, 31 9b and re-entrant grooves 320a, 320b are provided on the inside of the contact ring 317, the ribs 31 9a. 31 9b configured, when engaged with the cable sheath and contact surface 3 16 of the body 311, bending the sheath back during engagement and thereby increasing the force needed to pull the cable axially out of the cable gland assembly.

Illustrated in figure 4 is a cable gland assembly 400 with features in common with those shown in figures 1 and 2. In particular, the body 411 is of a similar form to that shown in figure 2. in that engagement with the housing 412 is by means of corresponding threaded sections 421, 422 on the body 411 and housing 412 respectively. The body 411 is therefore required to pass through from the side corresponding to the second face 124 of the wall 119 rather than from the side corresponding to the first face 123 of the wall 119 as in the body shown in figure 1. A knurled or otherwise machined face 420 is provided on the body 411 to 1 5 cause electrical bonding by penetrating insulating finishes on the wall 119, such as a paint or oxide layer.

Similarly to that shown in figure 1, the sheath contact ring 417 is provided with a stepped internal surface 425 to mechanically key into the sheath 426 of a cable 430 passing through the cable gland assembly 400. Tightening of the pusher body 414 on to the body 412 clamps the armour 426 of the cable 430 on to the contact surface 416 of the body 411. The contact surface 416 is preferably a tapered conical section of the body 411, the cone preferably having an angle to the longitudinal axis of the body 411 of around 10 degrees. The cone angle can, however, be greater or smaller than 10 degrees. Engagement of the seal pusher 415 on the pusher body 414 compresses the sealing ring 418 and forms a mechanical and environmental seal around the cable outer jacket 431. The cable 430 is then secured in place by both mechanical and electrical connections.

The use of a stepped surface on the ring 417 allows hand-tightening of the pusher body to be sufficient to provide a suitable electrical and mechanical connection to the cable armour. This reduces the possibility of over-tightening, which could result in damage to the armour 426. Typically, a quarter-turn after contact of the ring 417 with the cable armour 426 would be required to provide an adequate connection.

In the cable gland assembly 400 of figure 4, the sealing face 427 of the housing 412 engaging with the first surface 123 of the wall 11 9 is provided with sealing means in the form of a sealing ring 428 which may, for example. he in the form of a semicircular section protrusion extending around the sealing face 427 of the housing 412.

Illustrated in figure 5 is a modification to the cable gland assembly of figure 4, in which the sealing means is in the form of an 0-ring 528 positioned in a groove 529 in the face 527 of the housing 512. The o-ring is preferably composed of a resilient material such as a rubber, in order to provide an environmental seal to prevent fluid ingress between the first surface 123 of the wall 119 and the face 527 of the housing 512. The remaining features of the cable gland assembly 500 are otherwise similar to those shown in figure 4.

Illustrated in figure 6 is a further alternative cable gland assembly 600. An electrically conductive body 612 engages with an electrically insulating housing 613. The engagement feature providing a connection between the body 612 and housing 613 can be an external threaded section 614 of the body 612 engaging with a corresponding internal threaded section 624 of the housing 613.

Alternatively, the housing 613 can be moulded (e.g. injection moulded) on to the body 612, and the parts permanently connected by a suitable engagement feature in the body 612, for example in the form of one or more flanged protrusions extending into the housing 613.

A contact surface 619 in the form of an external cylindrical portion of the body is provided for electrical contact to a sheath of a cable positioned around the body.

The contact surface 619 may be roughened or knurled to provide a more secure mechanical and/or electrica] connection to the cable sheath. A flanged portion 616 may be provided on the body 612 to prevent slippage of the cable sheath when connected, as shown below in relation to figure 7.

A locking nut 617 and a clamping nut 625 are provided to respectively secure the body and housing to a wall and to clamp the outer surface of a cable passing through the assembly 600. The housing 613 and body 612 are clamped either side of the wall by means of a flanged portion 618 of the housing and the locking nut 61 7. A flexible portion of the housing, for example in the form of a plurality of flexible fingers 626. are configured to clamp around a cable when the clamping nut is engaged with the external threaded section 615 and tightened against the housing 613.

Shown in figure 7 is the cable gland assembly 600 in an assembled configuration, when secured to opposing first and second surfaces 123, 124 of a wall 119. A cable 732 is partially stripped of its outer jacket to expose a sheath 733, which may for example be in the form of an electrically conductive metal braided sheath.

Within the sheath 733 is a further electrically insulating sheath 734. protecting one or more strands of wire within the cable 732. The sheath 733 is clamped on to the contact surface 619 of the body 612 by means of a torsion spring 735 or by other means of forming a removable or permanent mechanical and electrical connection.

The locknut 617 is engaged with the external threaded section 614 of the body 612 and tightened against the second face 124 of the wall 119.

Advantages of the cable gland assemblies as described herein may include one or more of the following: The use of an electrically insulating housing reduces the risk of electric shock, as all outwardly-facing components of the cable gland assembly are insulated from any conductive parts. Products which need to be double insulated, i.e. with no conductive parts being immediately accessible, can benefit from this type of cable gland without loss of mechanical retention and electrical continuity for the cable armouring or braid.

Cable glands according to aspects of the invention can be made using an increased proportion of moulded plastic parts, replacing parts that have previously been metal. This can substantially reduce the manufacturing costs of the cable gland, particularly when the price of metals typically used for such components such as brass (comprising copper and zinc) are at historical]y high levels.

Cables having overall and/or individual shields and/or foil wrap protection can be successfully terminated with good electrical continuity and still retain the environmental benefits of an outer plastic gland.

The overall number of components can be reduced, through the use of parts (with reference to figure 1) such as the body 111 and housing 112 serving multiple functions. Further shroud components are not required to provide adequate insulation or environmental protection.

Overall, cable shrouds of the present invention combine the safety performance in terms of electrical insulation and environmental protection of plastic fittings with 1 5 the mechanical security and electrical continuity of metal to metal conductive paths for shield or armour terminations required for applications such as panel mounting of cables.

With reference to the accompanying figures, various features of the invention are composed of an electrically conductive, preferably metallic, material, including: the electrically conductive body 111, 211, 311, 411, 511, 612; the locknut 113, 617; and the sheath contact ring 117,217,317,417.

Various other features of the invention are composed of an electrically insulating, preferably polymeric, material, including: the electrically insulating housing 112, 212, 412, 512, 613; the pusher body 114,214,414; the seal pusher 115,215,415; and the clamping nut 625.

Electrically conductive components of the various cable gland assemblies described herein are preferably composed of metal, exemplary materials being brass or steel. Nickel-plated mild steel is preferably used for the body 111, 211, 311, 411 or locknut 113, 617, where a good electrical contact to the wall 119 is required. Electrically insulating components are preferably composed of polymeric materials such as thermoplastic or thennosetting polymers. One possible preferred material is a thermoplastic polyamide such as Nylon 66.

it is to be understood that optional and preferable features detailed above can, where appropriate, be used in combination with one or more of the different aspects of the invention as described herein.

Other embodiments are also intended to be within the scope of the invention, as defined by the appended claims.

Claims

CLAIM S

1. A cable gland assembly comprising: an electrically conductive body having an engagement feature, an external threaded section and an external contact surface adapted to connect to a sheath of a cable passing through the cable gland; and an electrically insulating housing adapted to directly engage with the engagement feature, the body and housing being adapted to clamp to first and second opposing 1 0 surfaces of a wall through a hole in the wall sized to receive the external threaded section of the body, wherein the engagement feature is adapted to secure the housing to the first surface of the wall.

2. The cable gland assembly of claim I comprising a locknut adapted to secure the body to the second surface of the wall by engagement of the locknut with the external threaded section of the body and clamping a face of the locknut to the second surface of the wall.

3. The cable gland assembly of claim 2 wherein the face of the locknut is adapted to provide a mechanical key to the second surface of the wall upon engagement with the external threaded section of the body such that electrical continuity is provided between the body and the wall.

4. The cable gland assembly of claim 1 wherein the engagement feature comprises an external flanged portion configured to interface with a corresponding internal flanged portion of the housing, such that engagement of the locknut clamps a face of the housing to the first surface of the wall.

5. The cable gland assembly of claim 4 wherein an internal surface of the housing is shaped to receive the external flanged portion of the body such that relative rotation of the body and housing around a longitudinal axis of the cable gland assembly is prevented.

6. The cable gland assembly of claim 5 wherein the external flanged portion of the body is in the form of a hexagonal shoulder and the internal surface of the housing is in the form of a corresponding hexagonal recess.

7. The cable gland assembly of claim I wherein the body comprises a flanged portion adapted to secure the body to the second surface of the wall.

8. The cable gland assembly of claim 1 or claim 7 wherein the engagement feature comprises a second external threaded section configured to engage with an 1 0 internal threaded section of the body.

9. The cable gland assembly of any preceding claim comprising: a pusher body having a threaded surface configured to engage with a corresponding threaded surface on the housing; and a ring sized to fit within the pusher body and around the contact surface of the body, such that engagement of the pusher body with the housing causes the ring to clamp an external sheath of a cable between the ring and the contact surface.

10. The cable gland assembly of any preceding claim wherein the contact surface is provided on a conical section of the body.

11. The cable gland assembly of claim 9 or claim 10 wherein the ring comprises a stepped internal surface adapted to engage with a cable sheath.

12. The cable gland assembly of claim 9 comprising: a seal pusher having a threaded surface configured to engage with a corresponding threaded surface on the pusher body; and a sealing ring sized to fit within and between the seal pusher and pusher body, such that engagement of the seal pusher causes the sealing ring to compress around a cable passing through the cable gland assembly.

13. The cable gland assembly of claim I wherein the engagement feature of the body comprises a second cxternal threaded section adapted to engage with an internal threaded section comprised within the housing.

14. The assembly of claim I wherein the housing is moulded around the engagement fearure of the body.

15. The assembly of claim 13 or claim 14 wherein the contact surface comprises an external cylindrical portion extending from the external threaded 1 0 Section of the body.

16. The assembly of claim 15 wherein the contact surface comprises a roughened surface.

1 7. The assembly of any of claims 13 to 16 wherein the housing comprises a flanged section configured to secure the body to the second surface of the wall and the housing to the first surface of the wall by means of a nut engaging with the threaded section of the proximal part.

1 8. The assembly of any of claims 13 to 1 7 further comprising a clamping nut configured to engage an external threaded section of the housing such that engagement of the clamping nut causes a flexible portion of the housing to mechanically clamp on to a cable extending therethrough.

19. A cable gland assembly comprising: an electrically conductive body having an external threaded section and an external contact surface adapted to connect to a sheath of a cable passing through the cable gland; and an electrically insulating housing adapted to directly engage with the engagement feature, the body and housing being adapted to clamp to first and second opposing surfaces of a wall through a hole in the wall sized to receive the external threaded section of the body, wherein the external threaded section is adapted to engage with an intenal threaded section of the housing to secure the housing to the first surface of the wall.

20. A cable gland assembly comprising: a metal part adapted to pass through a wall hole, the metal part having a cable sheath contact surface and means for engagement with a first surface of the wall; a plastic part adapted to provide opposing means for engagement with a 1 0 second opposing surface of the wall and means for engagement with the metal part.

21. A cable gland assembly substantially as described herein, with reference to the accompanying drawings.