GB2219697A

GB2219697A - Improvements in sealed cable glands

Info

Publication number: GB2219697A
Application number: GB8808739A
Authority: GB
Inventors: Alan Charles Durward Wales
Original assignee: CMP
Current assignee: CMP
Priority date: 1988-04-13
Filing date: 1988-04-13
Publication date: 1989-12-13
Anticipated expiration: 2008-04-13
Also published as: GB2219697B; GB8808739D0

Abstract

A cable gland assembly comprises a plastics gland body (12) through which a cable (36) passes. An internally threaded plastics compression nut (24) engages one end of the body. The nut is formed with a guide sleeve (26) which is a close fit within the body. The sleeve resists the tendency of the engaging threads on the body and nut to ride over one another as the nut is tightened. The radially inner surface (28) of the sleeve is tapered to urge a sealing ring into sealing contact with the cable. The other end of the gland body projects through an aperture in a wail and is secured in place by an internally threaded retaining ring (40). The ring has at least one radially projecting lug (42, 52) provided with an electrical connector (46), for connecting to the cable armouring (50). <IMAGE>

Description

IMPROVEMENTS IN CABLE GLANDS This invention relates to cable gland assemblies.

At the junction of a cable passing through an aperture in a wall, it is required in a large number of applications, effectively, to isolate the environments on either side of the wall. This may be, for example, to prevent dust, moisture or corrosive material from passing across the boundary created by the wall and/or to prevent combustible gases migrating across the boundary. In some instances, a cable gland at such a junction is required to provide an earth clamp for the braided armour wire sheath portion of the cable.

Cable glands are known which are made principally of metal. In some applications these have been superceded by plastics cable glands which are in particular demand in relation to plastics enclosures. In circumstances where the glands are exposed to the corrosive effects of environmental pollution, the usefulness of plastics in place of metals will be readily apparent.

However, earthing via plastics cable glands is less straight forward than was the case with their metal counterparts. When designing means for earthing in a cable gland, consideration has to be given to maintaining a reliable positive non-sparking connection arrangement which also maintains maximum clearances between the earth connection and the terminal of any electrical equipment associated with the cable or, indeed, any electrical equipment which is in the vicinity.

A plastics cable gland has been proposed which is, generally speaking, a replica of its metal equivalent.

Thus it has a compressive seal which is urged radially to engage sealingly the outer surface of the cable. In this case, worn or corroded metal parts of known cable glands can be replaced by plastics versions. However, plastics cable glands have been found to be significantly less rigid than the equivalent metal type. Consequently, the compression nut which is used to compress the seal is particularly prone to distortion as the seal is being compressed. Since the sealing force exerted by the compressed seal must be the same as before, the force exerted by the plastics compression nut must also be the same. Unfortunately when the plastics nut is tightened on the cable gland body, it has been known to jump threads before the appropriate sealing force is reached.Furthermore, if a compression nut is satisfactorily tightened there is a greatly increased risk that the engaged threads will jump at some time in the future due to expansion creepage caused by, for example, variations in temperature or absorption of moisture in the material of the cable gland. Because of this, plastics cable glands that are the equivalent of metal cable glands are generally considered unreliable.

It is an object of the invention to provide a more reliable cable gland than known cable glands but which can employ plastics components.

According to a first aspect of the invention, there is provided a cable gland assembly for a cable comprising a sleeve-like gland body having an aperture through which the cable passes, and a compression nut threadedly received at one end of the body to urge an annular sealing ring associated with the gland body into sealing engagement with the cable, and in which the compression nut includes a co-axial guide sleeve which co-operates with the surface of the gland body opposite that engaging the nut axially to guide the nut during assembly.

Thus, the tendency of the threads to ride over one another is resisted by the guide sleeve which becomes braced against the radially opposite surface of the gland as the assembly is tightened.

Preferably, the compression nut drives a compression ring, having a co-axial tapered surface, axially along the body to urge the sealing ring into sealing engagement with the cable. In this case it is preferable that the compression ring is integral with or constitutes the guide sleeve. It is also desirable that the taper of the compression ring extends away from the gland body.

Preferably, the compression nut is threadedly received on an external thread on the body. In this case, it is desirable that the guide sleeve extends radially inside the gland body.

According to a second aspect of the invention there is provided a retaining ring for securing a cable gland protruding through, for example, an aperture in a wall, the ring comprising a collar having a threaded internal surface for engaging a complementary thread on the cable gland and at least one outwardly extending lug having an electrical connector thereon.

Preferably, the lug extends radially outwardly from the collar. In this case, it may be desirable for the lug to be axially displaced out of the plane of an end face of the ring.

The present invention can be put into practice in several ways, some of which will now be described by way of example with reference to the accompanying drawings in which: Figure 1 is a partially longitudinally sectioned view of a first embodiment of the invention; Figure 2 is a partially longitudinally sectioned view of a second embodiment of the invention; Figure 3 is a retaining ring according to the second aspect of the invention; and Figure 4 is an alternative embodiment of a retaining ring according to the second aspect of the invention.

Figure 1 shows a cable gland assembly inserted in an aperture in a wall 10 of a housing. The assembly comprises a plastics gland body 12 which is secured in the aperture by a retaining ring 14 threadedly received on a first externally threaded sleeve portion 16 protruding through to the right-hand side of the wall 10 in figure 1. A flange 18 extends radially outwardly from the right-hand side of the threaded sleeve 16 and engages the wall 10 about the aperture. A dust and moisture seal ring 20 is accommodated in an annular channel of the face of the flange adjacent the wall 10.

A second externally threaded sleeve portion 22 extends from the flange 18 away from the aperture. A plastics compression nut 24 is threadedly received on the second sleeve 22. The nut 24 is formed with a radially inwardly extending portion and an inwardly turned annular guide sleeve 26 which protrudes into the passage for the cable formed in the gland. The radially outer surface 28 of the guide sleeve 26 is parallel to the radially inner surface of the second threaded sleeve portion 22 which is itself generally parallel to the axis of the overall assembly. The radially inner surface 28 of the guide sleeve 26 tapers radially inwards from the inside of the gland axially outwards.

As the compression nut 24 is screwed onto the second threaded sleeve portion 22 the tapered surface 28 engages the radially outer surface of a seal ring 30 which is seated on an annular ledge 32 inside the gland body. The ring 30 is thus urged radially inwardly into sealing engagement with an outer sheath 34 of a cable 36 passing through the gland.

The maximum clearance between the outer surface of the guide sleeve 26 and the inner surface of the second threaded sleeve portion 22 should be less than the depth of engagement between the thread on the second sleeve portion 22 and the thread on the compression nut 24 if the guide sleeve 26 is to assist in preventing the compression nut from jumping when it is tightened.

Preferably, the guide sleeve 26 is a close tolerance fit within the gland body 12 to prevent substantially all relative radial movement therebetween.

In its least stressed condition, the seal ring 20 is a cylindrical sleeve having sides generally parallel to the axis of the gland. When seated on the ledge 32 in the cable gland it protrudes beyond the axial extent of the second threaded sleeve portion 22. In its sealing position, with the compression nut 24 screwed in place, the deformed seal ring 30 still protrudes slightly beyond the axial extent of the compression nut 24. In this way, no water is allowed to accumulate within the gland assembly itself.

It has been found that the sandwich created by the outer threaded compression nut 24, the second threaded portion 22 and the guide sleeve 26 create an effective thickness of material which also toughens the assembly.

Coupled with the reduced length of the gland, the impact loads which the gland is able to withstand are considerably increased.

Clearly, the cable gland assembly could be used as a whole unit or the various plastics components could be utilised individually to replace worn or corroded parts in existing cable glands.

Figure 2 shows a second embodiment of a cable gland which is in many respects similar to that in Figure 1.

Consequently, like numerals have been used where appropriate on like parts. The second embodiment differs in that a modified retaining ring 38 is used.

The ring 38 is illustrated in more detail in Figure 4.

It comprises a metal collar 40 having a threaded inner surface which is received on the first threaded sleeve portion 16 of the gland body. A pair of lugs 42 extend radially from the collar. The lugs are axially displaced away from an end face 44 of the collar 40 which engages the wall 10 when the cable gland is retained. A U-section clamping plate 46 embraces each lug 42 from the face remote from the wall 10. Each plate 46 is held in place by a bolt 48 passing through the plate and into a threaded hole in each lug 42.

This type of retaining ring is used where it is required to provide an earth point for an armour wire earthing braid 50 of the cable at the junction of the cable with the wall 10. In this embodiment, the earthing braid 50 is fed through apertures in the first sleeve portion 16, though it may simply be taken out through the end of the sleeve portion 16. A wire leading to earth and the gathered braid 50 are fed beneath the clamping plate 46 on either side of the bolt 48.

In an alternative embodiment of the retaining ring a single earth connection point using a single lug can be used, as shown in Figure 3. In this particular form the lug 52 extends in the plane of the face of a collar 54. In this case, the retaining ring is designed to be used with a clearance washer to space the lug 52 from the wall 10. The lug would of course be axially displaced as before and indeed the lugs in the previous embodiment could be in the plane of the collar.

In all cases, the rings allow for maximum electrical clearance from the electrical components within the enclosure defined by the wall 10.

Two lugs are used to permit multiple connections in panel earthing or where extra connections are required due to electrical regulations limiting the number of earth conductors which can be connected to such an earth point to not more than two per clamp.

Claims

1. A cable gland assembly for a cable comprising a sleeve-like gland body having an aperture through which the cable passes, and a compression nut threadedly received at one end of the body to urge an annular sealing ring associated with the gland body into sealing engagement with the cable, and in which the compression nut includes a co-axial guide sleeve which co-operates with the surface of the gland body opposite that engaging the nut axially to guide the nut during assembly.

2. An assembly as claimed in claim 1, wherein a compression ring is urged axially along the body by the compression nut to compress the sealing ring into sealing contact with the cable, one or both of the compression ring and sealing ring having an annular tapered surface, which surface(s) urges the sealing ring radially inwardly as the nut is tightened.

3. An assembly as claimed in claim 2, wherein the compression ring is formed integrally with the compression nut.

4. An assembly as claimed in claim 2 or 3, wherein the tapered surface is formed on the compression ring and tapers radially inwardly away from the gland body.

5. An assembly as claimed in any preceding claim, wherein the compression nut is internally threaded and is received on a complementary external thread on the gland body.

6. An assembly as claimed in any preceding claim, wherein the guide sleeve extends radially inside the gland body.

7. An assembly as claimed in any preceding claim, wherein the gland body and/or compression nut are made of plastics material.

8. A retaining ring for securing a cable gland protruding through, for example, an aperture in a wall, the ring comprising a collar having a threaded internal surface for engaging a complementary thread on the cable gland and at least one outwardly extending lug having an electrical connector thereon.

9. A ring as claimed in claim 8, wherein the lug extends radially outwardly from the collar.

10. A ring as claimed in claim 8 or 9, wherein the lug is axially displaced out of the plane of an end face of the ring.

11. A cable gland assembly for a cable substantially as specifically described herein with reference to Figure 1 or 2 of the accompanying drawings.

12. A retaining ring for securing a cable gland protruding through an aperture in a wall substantially as specifically described herein with reference to Figure 3 or 4 of the accompanying drawings.