AU774888B2

AU774888B2 - Electrical cable gland permitting of internal inspection

Info

Publication number: AU774888B2
Application number: AU56572/01A
Authority: AU
Inventors: Franz Lackinger
Original assignee: ELECTRO WIN Ltd
Current assignee: CCG AUSTRALASIA Pty Ltd
Priority date: 2000-05-31
Filing date: 2001-05-11
Publication date: 2004-07-08
Anticipated expiration: 2021-05-11
Also published as: AU5657201A; GB2368201A; GB0201224D0; WO2001093395A1; GB2368201B

Description

WO 01/93395 PCT/IB01/00819

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ELECTRICAL CABLE GLAND PERMITTING OF INTERNAL INSPECTION FIELD OF THE INVENTION This invention relates to an electrical cable gland of the general type adapted to be employed for terminating armoured electrical cables where they enter an electrical connection box or other housing in which the electrical conductors of the cable are connected to terminals of one form or another.

More particularly, the invention relates to an electrical cable gland of the type having an armour clamp in the form of a cone having an outer conical surface for engaging the inside of the armouring of the cable and adapted to cooperate with a clamping ring having an inner surface of complementary conical shape so that the armouring can be clamped firmly between the two conical surfaces.

Still more particularly, the invention relates to an electrical cable gland of this type in which an outer body part is capable of being at least partially removed to permit inspection of the condition of the armour clamp at any required time after installation of the cable gland and without disturbing the armour clamp itself.

It is to be understood that the term armouring is used in a broad sense in this specification in that the armouring could be a mechanically protective layer in the form of longitudinally extending relatively stiff wires of significant thickness arranged to form an electrically conductive armour layer (generally used additionally for earthing purposes) between the inner and outer insulating sheaths and having substantial tensile strength; or the armouring could be in the form of fine, substantially more flexible, optionally braided, WO 01/93395 PCT/IBO1/00819 wires or metal tape not having such substantial tensile strength and often serving one or more functions including reinforcing the cable; providing an electromagnetic shield; and/or simply an electrically conductive earth.

BACKGROUND TO THE INVENTION Preventative maintenance of installations, and, of particular importance to this invention, electrical installations, is becoming more and more commonplace. As a part of such maintenance it is often necessary to io inspect cable glands embodied in any electrical installation to check for corrosion or other possible defects of the armour clamp assembly as well as any seals of the cable glands. In order to do this a part of the cable gland body which covers the armour clamp assembly must be removed without disturbing the clamp so that it can be inspected. This is usually done by unscrewing one body part at the cable entry end of the cable gland and sliding it along the cable to expose the armour clamp.

In cases in which a cable gland has a loose clamping ring this does not present any difficulties as the body part of the cable gland which covers the ring, and in fact urges it over the cone, can simply be unscrewed and slid along the cable by a short distance without disturbing the armour clamp.

On the other hand, if the ring is integral with, or permanently associated with, the relevant part of the gland, such inspection is not possible without disturbing, and in fact undoing, the armour clamp, which is usually not desireable or required. It is to be noted that the armour clamp, once installed, may become effectively locked in its installed condition by virtue of the fact that the taper of the conical surfaces is generally a locking taper of about degrees to the axis of the gland. Appreciable force may thus be required to undo the armour clamp. Thus a loose clamping ring would generally be preferred in installations requiring such periodic inspection.

3 Such maintenance may also involve inspection of the inner seal of a cable gland having such a seal. This requires that both the ring and the cone of the armour clamp be separable from their associated parts of the body of the gland for the purposes of inspection.

Notwithstanding the aforegoing, applicant is of the view that the original installation of a cable gland can be substantially facilitated and rendered less susceptible to difficulties associated with the loss or dropping of loose 0io components such as a loose clamping cone and/or a loose clamping ring by simply avoiding the use of such loose components insofar as is possible.

o The reason for this is that with loose components a technician installing a gland may have difficulty holding all the necessary components; may drop *go and possibly lose a cone or ring; and may close the gland with the dropped Io: 15 or lost part missing with possible serious consequences.

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g o 0 •g.o* •go• 0 00O• SUMMARY OF THE INVENTION In accordance with this invention there is provided a cable gland comprising a body and an armour clamp assembly wherein the latter has an armour clamping cone associated with a first body part and a cooperating armour clamping ring associated with a second body part which forms an outer cover to the clamping ring, and wherein the clamping ring is held releasably or temporarily captive relative to the said second body part at least prior to installation of the gland whilst permitting separation of said second body part ro from the clamping ring in an installed position thereof in the armour clamp, the conical clamping surfaces having at least one substantially circumferentially extending ridge standing proud of the conical surface and shaped, in cross-section, to present a contact edge sufficiently sharp to bite slightly into the outer surface of armour wires engaged thereby in use.

Further features of the invention provide for the cable gland to have a twopart construction with the cone being held captive in the first body part and the clamping ring being held at least temporarily captive in a second body part with the two body parts being movable axially by virtue of cooperating screw threads thereon; and for the cable gland to embody both inner and outer compression seals for sealing onto the inner and outer sheaths of a cable.

The clamping ring may be held releasably or temporarily captive relative to the second body part by any suitable means and, in particular, by means of an resilient ring, such as a resilient clip of generally ring shape, or an elastomeric ring such as an O-ring, either cooperating frictionally with the second body part and clamping ring, or cooperating with a groove in either the inner surface of the second body part or the outer surface of the ring, or both. In such a case it is preferred that the clamping ring be held releasably captive relative to the said second body by means of a resilient clip of generally ring shape seated loosely in a circumferentially extending groove in the outer surface of the ring and cooperating with a groove in the inner surface of the second body part. The groove in the body part preferably has a lead-in taper to facilitate unclipping of the ring from the body part.

Alternatively, the armour clamping ring could be temporarily adhered to the second body part of by means of any tacky substance or even by means of a weak adhesive bond which is capable of being broken during installation so that the ring becomes a separate component automatically by virtue of the torsional forces exerted on the bond during installation.

go Preferably, the armour clamping cone is, as indicated above, also held captive relative to its associated body part, namely the first body part of the cable gland. Whilst this can be achieved in many different ways it is 5 Is preferably done by means of a tubular extension extending coaxially away from the conical clamping surface and into the open end of a bore in the first S-body part and wherein the tubular extension has a peripheral flange on its outer surface for retaining it within said bore by cooperation with an inwardly directed formation at said open end of the bore. Preferably the formation on the bore is in the form of a circumferential ridge directed inwards with the inner peripheral edge of the ridge and the outer peripheral edge of the flange being dimensioned and configured to cooperate with each other to hold the clamping cone releasably captive relative to the said first body part by means of an interference fit which permits separation of the cone from the first body part by suitable manipulation of the cone relative thereto.

In the case of an inner seal, the seal will generally be accommodated in the bore of the first body part and will be compressed axially by the free end of the extension of the cone. In this instance the seal will generally hold the flange on the extension in approximately square-on relationship relative to the ridge at the end of the bore.

6 It is to be understood that the term interference fit is intended to mean that the dimensions and configuration of the ridge and flange are such that, when they confront each other square-on, they can only pass one another with considerable force being applied, very much in the manner of press fit.

However, if the cone and its extension are flexed out of the plane of the axis of the first body part about a transverse axis so that the flange contacts the ridge only in two approximately diametrically opposed positions, the flange can be relatively easily clipped inwardly or outwardly past the ridge which preferably has a smooth curved shape in cross-section in order to facilitate io this.

In a preferred embodiment a series of spaced substantially circumferentially extending ridges on both of the clamping surfaces and the ridges are provided and are of saw tooth shape in section with the saw tooth being orientated so as to resist removal of the cone or ring from the armour wires.

The term substantially circumferentially is used to include a helix of small pitch and thus the ridges could be successive convolutions of a continuous helical ridge very much resembling a screw thread following a conical path.

In order that the invention may be more fully understood one preferred embodiment thereof will now be described with reference to the accompanying drawings.

WO 01/93395 PCT/IB01/00819 7 BRIEF DESCRIPTION OF THE DRAWINGS In the drawings:- Figure 1 is an elevation of a cable gland according to the invention with the upper half thereof shown in section; Figure 2 is an enlarged view of the clamping cone and ring illustrated in Figure 1; Figure 3 is an elevation similar to Figure 1 but showing the body parts of the gland separated from the armour clamp to permit inspection thereof; Is Figure 4 is a very much enlarged sectional view of the damping cone and ring illustrated in Figure 3; and, Figure 5 is a very much enlarged sectional view illustrating the cooperation of the clamping cone and associated first body part of the cable gland.

DETAILED DESCRIPTION WITH REFERENCE TO THE DRAWINGS In the embodiment of the invention illustrated in the drawings a cable gland, generally indicated by numeral is composed of two body parts and the first body part of which has an armour clamping cone held captive relative to it and the second body part of which has a clamping ring held releasably captive relative to it. The two body parts have cooperating screw threads whereby they may be urged axially towards each other to move the cone into the ring WO 01/93395 PCT/IB01/00819 8 The cone has a rearwardly directed extension which simultaneously compresses an elastomeric inner compression seal in well established manner. The entry end of the gland has an elastomeric outer compression seal which is independently brought into service by means of a union nut (10) screwed onto the entry end of the body.

The cone and clamping ring have cooperating conical clamping surfaces indicated by numerals (11) and (12) respectively. The cone angle of these surfaces is substantially conventional (for example a cone angle of to 20 degrees or, in other words, 10 degrees to the axis of the gland) and of self locking type. These surfaces are adapted to clamp the armour wires (13) of a cable between them (see Figures 3 and 4).

Reverting now to the releasable attachment of the clamping ring to the second body part, this, in this particular embodiment of the invention, is achieved using a resilient wire clip (14) in the form of an incomplete ring and which engages in complementary grooves (15) and (16) in the inner surface of the second body part and the outer surface of the clamping ring respectively. The cross-sectional size and resiliency of the clip are chosen so that it effectively holds the clamping ring captive relative to the second body part so that the ring does not fall out of the second body part during handling and installation of the gland.

In the event, however, that it is required to remove the second body part to permit of inspection of the armour clamp, the clamping ring and second body part separate simply by unscrewing the second body part from the first body part and moving it axially away from the first body part to a position illustrated in Figure 3 in which the clamp is clearly visible and capable of proper inspection. During this movement the clip contracts radially into the groove in the outer surface of the clamping ring to enable it to slide out of the second body part. In order to enable this to take place most easily, the groove (15) in WO 01/93395 PCT/IB01100819 9 the inner surface of the second body part has a smoothly tapered lead-in surface (17) against which the clip can slide as it contracts radially.

Reverting now to the clamping cone and its relationship, with its associated body part, namely the first body part and with particular reference to Figure 5 of the drawings, the extension of the cone has, at its free end (18) remote from the clamping surface (11) an outwardly directed flange (19) which is located within the confines of the bore (20) in the first body part which accommodates the inner seal The outer periphery (21) of the flange cooperates by way of an interference fit as described above with the inner periphery (22) of a circumferentially extending ridge (23) at the open end of the bore As illustrated in Figure 5, the ridge has a smoothly rounded cross-sectional configuration which enables the interference fit described above to be given full effect. The flange is effectively held captive when it is square-on to the ridge as it requires considerable force to be exerted on it to pass the ridge in either direction, the force required being of the order of that which would be necessary if the two parts were a press fit. However, if the cone and its extension are flexed out of the plane of the axis of the first body part about a transverse axis and as illustrated by arrow in Figure 5, then the periphery of the flange contacts the ridge in only two diametrically opposed locations and the flange can be clipped into and out of the bore quite easily using manual force. Simply for the purpose of example and illustration it has been found that in the case of a brass cone having a flange with an outer diameter of 25,17 mm, an inner diameter of the ridge of about 25.12 to 25,14 mm operates effectively.

This being so, when it is required to inspect both the armour clamp and the inner seal of a cable gland, the two body parts can simply be unscrewed relative to each other and the clamping ring disengaged from the second body part as described above. At this stage the cone can be manipulated as WO 01/93395 PCT/IB01/00819 indicated above, and the flange can be disengaged from the ridge at the entrance to the bore of the first body part of the cable gland. The inner seal within the first body part is then accessible for inspection and optional removal for such purpose. All this can be achieved whilst the armour wires of the cable remained firmly clamped between the cone and ring as illustrated clearly in Figure 3.

As a general rule it would be expected that the armour clamp would remain locked in its. operative position with conventional surface finishes on the clamping surfaces of the clamping cone and the clamping ring. However, it is preferred to ensure that the armour clamp remains properly engaged during opening of the gland for inspection purposes and with this in view, the clamping surfaces are formed with a series of integral, substantially circumferentially extending ridges (24) of narrow width and having a sharp edge.

Conveniently the ridges can be successive convolutions of a helically extending ridge having a small pitch so that successive convolutions are very much like a conventional fine screw thread but with the space between successive convolutions being generally greater than the height of the ridge.

The cross-sectional shape of the ridges is preferably of saw-tooth configuration with a roughly radial face (25) and an inclined face The roughly radial face is, in each case, directed towards the direction in which the cone or clamping ring would have to move in order to disengage the armour clamp. It will be appreciated that a helical ridge can be easily formed during the machining process used to form the cone and ring and accordingly very little, if any, additional cost is involved in forming the ridges.

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, as regards the captive clamping cone, and as an alternative to the resilient clip, an elastomeric ring of the nature of an O-ring may be employed. Also, only one of the components need be provided with a groove in cases where frictional engagement with the surface of the other component will be adequate to hold on the ring captive at all times prior to installation. As a further alternative, the clamping ring could be temporarily bonded to the second body part using adhesive or even a suitably tacky substance.

The invention therefore provides a cable gland in which the gland can be supplied in the form of two subassemblies for easy and reliable installation io whilst it allows for periodic inspection of the armour clamp, and if required also the inner seal of an electrical cable gland of this general type The reference to any prior art in this specification is not, and should not be taken as, an acknowledgment or any form of suggestion that that prior art forms part of the common general knowledge in Australia. i ••%15 Throughout this specification and the claims which follow, unless the context requires otherwise, the word "comprise", and variations such as "comprises" and "comprising", will be understood to imply the inclusion of a stated integer or step or 20 group of integers or steps but not the exclusion of any other integer or step or :20 group of integers or steps.

Claims

1. A cable gland comprising a body and an armour clamp assembly wherein the latter has an armour clamping cone associated with a first body part and a cooperating armour clamping ring associated with a second body part which forms an outer cover to the clamping ring, and wherein the clamping ring is held releasably or temporarily captive relative to the said second body part at least prior to installation of the gland whilst permitting separation of said second body part from the clamping ring in an installed position thereof in the armour clamp, the conical clamping surfaces having at least one substantially circumferentially extending ridge standing proud of the conical surface S.and shaped, in cross-section, to present a contact edge sufficiently sharp to bite slightly into the outer surface of armour wires engaged 0* thereby in use.

2. A cable gland as claimed in claim 1 in which the clamping ring is held releasably or temporarily captive relative to the second body part by means selected from the group consisting of an resilient clip of 20 generally ring shape, and an elastomeric ring, cooperating with a ooo• :groove in at least one of the inner surface of the second body part and the outer surface of the clamping ring.

3. A cable gland as claimed in claim 2 in which the clamping ring is held releasably or temporarily captive relative to the second body part by means of a resilient clip of generally ring shape seated loosely in a circumferentially extending groove in the outer surface of the clamping ring and cooperating with a groove in the inner surface of the second body part.

4. A cable gland as claimed in either one of claims 2 or 3 in which any groove in the second body part has a lead-in taper to facilitate unclipping of the ring from the body part.

5. A cable gland as claimed in claim 1 in which the clamping ring is held releasably or temporarily captive relative to the second body part by means of a tacky substance or adhesive bond which is capable of being broken during instaliation so that the ring becomes a separate component automatically by virtue of the torsional forces exerted on the bond during installation.

6. A cable gland as claimed in any one of the preceding claims in which *OO. the armour clamping cone is held captive relative to the first body part of the cable gland. 1.

7. A cable gland as claimed in claim 6 in which the clamping cone has a tubular extension extending coaxially away from the conical clamping S surface and into the open end of a bore in the first body part and wherein the tubular extension has a peripheral flange on its outer 20 surface for retaining it within said bore by cooperation with an inwardly fee* :06. directed formation at said open end of the bore.

8. A cable gland as claimed in claim 7 in which the formation on the bore is in the form of a circumferential ridge directed inwards with the inner peripheral edge of the ridge and the outer peripheral edge of the flange being dimensioned and configured to cooperate with each other to hold the clamping cone releasably captive relative to the said first body part by means of an interference fit which permits separation of the cone from the first body part by suitable manipulation of the cone relative thereto. 14

9. A cable gland as claimed in claim 1 in which the conical clamping surfaces each have a series of spaced substantially circumferentially extending ridges.

10. A cable gland as claimed in claim 9 in which the ridges are of saw tooth shape in section with the saw tooth being orientated so as to resist removal of the cone or ring from the armour wires.

11. A cable gland as claimed in any one of the preceding claims in which the cable gland has a two-part construction wherein the clamping cone is held captive relative to the first body part and the clamping ring is held at least temporarily captive in a second body part with the two body parts being movable axially by virtue of cooperating screw threads thereon.

12. A cable gland, substantially as hereinbefore described with reference to the drawings and/or Examples. DATED 30 March 2004 20 ELECTRO-WIN LIMITED By DAVIES COLLISON CAVE Patent Attorneys for the applicant