GB2337373A - Snap-fit cable glands - Google Patents

Abstract

A cable gland 1 which snap-fits into a housing 10 has a rubber flange 6 and optionally a sealing washer 7. The rubber moulding may be integral with the body 2 or may interlock with a plastic body (23, Fig 2). Alternatively the snap-fit may be provided by hard flexible plastic fingers (31, Fig 3). Alternatively, the snap-fit may be provided on a separate member 89 which snaps into an internal groove 87 of the gland after going through the housing. Alternatively flexible fingers (109, Fig 6) may be provided on the housing to go into a groove (107) on the gland.

Description

1, 2337373 1 cable Glands This invention relates to electric cable glands

for use in terminating cables into connecting boxes or other apparatus having a housing with an aperture in a wall of the housing for receiving the gland. It includes termination methods and terminations in which the glands are used.

In current practice, cable glands (whether of metal, plastics material or a combination) are mounted in circular apertures in the housing by means of a threaded annular spigot projecting from one end of the gland to pass inwardly through the mounting aperture and a mating threaded backnut on the inside of the wall. This requires access to the inside of the apparatus for the placing and tightening of the backnut, usually requiring one spanner inside the apparatus and another outside. This can often be difficult and can require a considerable time to complete satisfactorily in some site conditions. It also implies that the gland must project into the apparatus at least the thickness of the backnut (and typically more than that, as the wall thickness may vary and the spigot length, generally speaking, does not).

The present invention is based in part on the realisation that the mounting of a cable gland only needs to provide security against relatively small tensile forces and in some cases a modest degree of resistance to rotation and/or a fluid- tight seal, and that the conventional screwed mounting is often substantially over-engineered.

In accordance with the invention, there is provided a termination for an electrical cable, the termination including a cable gland comprising an annular body having a bore running the length of the annular body with means for securing an electric cable end passing though the bore of the 1 J 1 2 annular body to a housing having an aperture therein, the termination further including resilient mounting means arranged to snap-fit into retaining means of corresponding dimensions to thereby secure the body to the housing.

Many design options are available within this inventive concept. The snap fit may be irreversible without damage to some part of the assembly, or it may be reversible by the use of an appropriate tool or mechanism, or it may be reversible but provided with a locking means to prevent accidental disengagement. The resilient mounting means may be a resilient extension of the body of the gland, it may be separate from the body, or in special cases it may be provided on the housing, around the aperture. A resilient extension may be integral with the body, or it may be an attachment. The body and the extension, each independently, may be of metal or of an insulating material or a combination of both, so providing a range of earthing (grounding)/insulating options. The end face of the body may be ridged or roughened to offer resistance to rotation, or a lockwasher may be fitted for the same purpose; alternatively a resilient washer may be fitted adjacent the end of the body to provide a fluid- tight seal to the wall around the aperture and some resistance to rotation. Where feasible (probably only in a dedicated range of accessories), the aperture may be non-circular and the resilient extension shaped to interlock with it, or the body or extension may be provided with a projecting member for engarement with a separate aperture in the apparatus wall, in each case positively preventing rotation or limiting its extent.

The cable securing means may be entirely conventional and the body may also support means for providing any of the features that are ordinarily available in cable glands, for 1 9 3 example for making a fluid-tight seal to an inner and/or an outer layer of the cable and for earthing one or more metallic layers of the cable, or for shrouding for sealing and/or corrosion protection.

When the resilient mounting means is of non-metallic material that is relatively soft and rubbery, it may be a simple spigot with an external flange that is externally tapered from a narrow distal end that is small enough to enter the aperture for which the gland is designed to a wider proximal end that can be deformed by engagement of the tapered surface with the edges of such aperture to pass through the aperture but will then spring back to prevent the flange from repassing in the other direction.

when the resilient mounting means is of harder material, either a relatively hard resilient material or a metal, it preferably comprises a plurality of individual resilient fingers arranged around the periphery of the aperture in which the gland is designed to be mounted, each having a camming face for engagement with the edge of such aperture to deflect the finger and allow passage though the aperture and an abutment surface to engage behind the aperture when the camming surface has passed through it. If the number of fingers is large and the spaces between them are small, this will superficially resemble the structure described in the preceding paragraph. At the other extreme, if the material is strong enough, three fingers (preferably at 1200 positions) may be sufficient.

Similarly, where the resilient mounting means is separate, it may be an annulus - made of a plastics material or metal - also having a plurality of individual resilient fingers, each having a camming face, which is arranged to snap-fit into an annular groove provided on the main body of 1 4 the cable gland. Further, (in a purpose-made "system" of components) the resilient fingers may be provided around the aperture itself, and also arranged to snap-fit into an annular groove provided on the main body of the gland. -In both cases, the number of fingers can be chosen to suit the particular requirements and dimensions of the application.

In all of these cases, the security of mounting may be increased, if desired, by inserting a tube of relatively hard material (metallic or nonmetallic) into the bore of the extension after it has been snap fitted into the aperture. Such tube might have other functions in the gland: for example, it might provide an earth connection through a gland body of insulating material.

If the resilient mounting means is separate from but attached to the body of the gland (usually because it is made of different material) it may be snap-fitted to the body or connected to it in any way appropriate to the materials being used. For example, a metal extension may be snap-fitted into a groove in the bore of the body or may be moulded into a body of plastics material. If desired, they could be screwed together, since the extension may be fitted to the gland by machinery, or at least under conditions of easy access in the factory.

The invention will be further described, by way of example, with reference to the accompanying drawings in which Figures 1 to 6 are partly sectioned "exploded" views of a different form of gland in accordance with the invention, showing the parts separated but in order for assembly.

In the simple form of gland shown in Figure 1, a body 1 comprises a rubber moulding 2 having embedded in it and bonded to it a simple tubular metal insert 3 having an internal (female) screw thread extending for all or part of its length. At one end of the moulding 2 and formed in one piece with it is an extension 4 comprising a plain tubular part 5 and a flange 6 which is tapered on its outward-facing surface and square on the surface facing the main part of the body. A resilient sealing washer 7 is first passed over the flange 6 to abut the end face 8 of the body 1 and then the flange 6 can be inserted into an appropriate aperture 9 in a housing wall 10. This can be done either by first inserting one edge of the flange 6 through the aperture and rocking until the remainder snaps through the aperture, or by presenting the flange 6 centrally and square to the aperture and then tapping the body to cause the whole flange to snap through. The washer 7 functions to take up clearances between the wall 10 and the end face 8, and should be compressible enough to allow for variations in thickness of the wall 10: alternative washers differing in thickness may be provided to allow for extreme variations in wall thickness if necessary. The washer 7 may also provide a fluid-tight seal. A sealing ring 11 dimensioned to push into the bore of the metal insert 3 and a male gland nut 12 dimensioned to mate with its screw thread completes a gland providing an "outer" seal only (in relation to cable glands, an "outer" seal is a seal to the outer sheath or jacket of a cable, as distinct from an "inner" seal to an inner sheath or bedding under armour or other layers of the cable - reference to an "outer" or "inner" seal does not imply the presence of the other).

The gland of Figure 2 is wholly nonmetallic but is otherwise substantially identical with that of Figure 1 except that the rubber moulding 22 does not enclose the threaded tube 23 of hard plastics material, but instead enters its bore and interlocks with it by entering an annular groove 25. The moulding 22 may be wholly separate from the 6 tube 23 and simply force-fitted into it (in which case a hard flanged tube 26 may be inserted, preferably after fitting to the apertured wall 10, to restrict deformation of the moulding and resist its separation from either the tube or the wall), or they may be bonded together with a suitable adhesive. Other alternatives (depending mainly on the thermal properties of the material) include forming the moulding in situ in a preformed tube, say of heat- resisting thermosetting resin, or forming the tube in situ, say by thermoplastic injection moulding, on a preformed rubber moulding.

In modifications of the design of Figure 2, one or more of the members 12, 23 and 26 may be of metal without substantial alteration (except that provision for earthing say a tapped bore in the tube 23 - will usually be needed).

Figure 3 shows a more complex design of gland, suitable for a cable having wire armour layer enclosed in an outer sheath and providing mechanical securing (but not earthing) for the armour and an outer seal. The gland body 30 is a onepiece moulding of a hard flexible plastics material (for example polypropylene, high-impact polystyrene or a suitable nylon) including an extension formed by an annular group of individual flexible fingers 31 each having (a) an inclined camming surface 32 for engaging the edge 33 of the aperture in the wall 10 in which the gland is to be mounted and thereby bending the finger until they enter the aperture and (b) an abutment face 34 for engaging the inside face of the gland once they have passed through it. The gland is otherwise conventional and comprises an armour cone 35, armour ring 36, barrel 37, sealing ring 38, skid washer 39 and gland nut 40. Except for the sealing ring, all of these might be of metal or of non- metallic insulating material.

1 7 In a further embodiment of the invention, illustrated in Figure 4, there is provided an "indoor" cable gland 50 for terminating a cable having a single layer of armour wires. The main body 51 of 'the gland 50 is an annular member 61 having an external screw thread 60 and an armour cone 55. At one end of the annular member 61 there is an extension 66, similar to that illustrated in Figure 3, and also comprising an annular group of individual flexible fingers 52 each having, an inclined camming surface 53 for engaging the edge 33 of an aperture 63 in the housing wall 10 in which the gland 50 is to be mounted and thereby bending the fingers 52 until they enter the aperture 63. The flexible fingers 52 also have an abutment face 54 for engaging the inside face 64 of the wall 10 once they have passed through the aperture 63.

The gland 50 is otherwise conventional (except that it makes no provision for electrical connection to the armour wire, it being assumed that they are earthed elsewhere) and comprises the armour cone 55 having a frustoconical outer surface 56, and a gland nut 57, having an inner screw thread 65 for engaging with the external screw thread 60 provided on the annular member 61, and a corresponding frusto-conical inner surface 59 designed to grip the ends of armour wires splayed out onto the armour cone 55 when the gland nut 57 is screwed onto the thread 60.

Figure 5 illustrates yet another embodiment of the present invention, and which is also an "indoor" cable gland for terminating a cable having a single layer of armour wires. As in the previous embodiment described above, the main body 81 of the gland 80 is an annular member 82 having an external screw thread 83 and an armour cone 84. Provided on the interior surface 85 of the annular member 82 at the end 86 remote from the armour cone 84, is an annular groove 1 8 87 running around the inner circumference, which defines an inwardly directed flange 88 at the remote end 86 of the annular member 82. There is also provided an annulus 89 made of plastics material or metal - having an annular group of outwardly extending individual resilient fingers 90. Each of the fingers 90 has an inclined camming surface 91, and an abutment face 92. For terminating a cable, the remote end 86 of the annular member 82 is placed against the housing wall 10 around the aperture 63 provided therein, and the annulus 89 inserted through the aperture 63 from inside the housing wall. The inclined camming surface 91 engages the edge 93 of the inwardly directed flange 88 when the annulus 89 is inserted through the aperture 63 in the housing wall 10 in which the gland 80 is to be received thereby bending the fingers 90 until they ride over the flange 88 and snap fit into the groove 87. The abutment face 92 of the flexible fingers 90 then engages the inside face 94 of the groove 87. Thus the remote end 86 of the annular member, and therefore the whole of the main body 81 is held in place against the housing wall 10. The gland 80 is otherwise conventional and comprises the armour cone 84 having a frusto-conical outer surface 95, and a gland nut 98, having an inner screw thread 97 for engaging with the external screw thread 83 provided on the annular member 82, and a corresponding frusto-conical inner surface 96 designed to grip the ends of armour wires splayed out onto the armour cone 84 when the gland nut 96 is screwed onto the thread 83.

Figure 6 illustrates a further embodiment in which reflex bent flexible fingers 109 are provided around the circumference of the aperture 63 in the housing wall, and extend outwardly of the housing wall 10. This gland 100 is also an "indoor" cable gland for terminating a cable having a 9 single layer of armour wires. As in the previous embodiments described above, the main body 101 of the gland 100 is an annular member 102 having an external screw thread 103 and an armour cone 104. Provided on the outer surface 105 of the annular member 102 at the end 106 remote from the armour cone 104. there is provided an annular groove 107 running around the outer circumference, thereby defining an outwardly directed flange 108 at the remote end 106 of the annular member 102. The annular groove 107 is arranged to co- operate with reflex bent flexible fingers 109 provided around the aperture. The outwardly directed flange 108 has an outer camming surface 110 and an abutment face 111. To connect the gland 101 to the housing, the main body 101 is pushed against the resilient fingers so that the reflexed portion 112 of the resilient fingers 109 abuts the camming surface 110 and are thereby bent so that they ride over the flange 108 and snapfit into the groove 107, the end portion 113 of the resilient fingers 109 abutting the abutment face 111 to thereby prevent the main body 101 of the gland 100 from moving away from the housing wall 10. As with the other embodiment s described with respect to Figures 4 and 5, the gland 100 is otherwise conventional and comprises the armour cone 104 having a frusto-conical outer surface 115, and a gland nut 116, having an inner screw thread 117 for engaging with the external screw thread 118 provided on the annular member 102, and a corresponding frusto-conical inner surface 119 designed to grip the ends of armour wires splayed out onto the armour cone 104 when the gland nut 116 is screwed onto the external screw thread 118.

As will be understood by persons skilled in the art, variations are possible within the scope of the present invention, for example, the resilient fingers could have other configurations. In addition, combinations of the snapfitting features of various embodiments described above are possible.

11

Claims (4)

1. A termination for an electrical cable, the termination including a cable gland comprising an annular body having a bore running the length of the annular body with means for securing an electric cable end passing though the bore of the annular body to a housing having an aperture therein, the termination further including resilient mounting means arranged to snap-fit into retaining means of corresponding dimensions to thereby secure the body to the housing.

2. A termination as claimed in claim 1, wherein the resilient mounting means is a resilient extension at one end of the body and the retaining means is the aperture in the housing, the resilient extension being shaped to snap-fit into the aperture of corresponding,dimensions and thereby secure the body to the aperture.

3. A termination according to claim 1 wherein the resilient mounting means is an annular member having a resilient members, and the retaining means is an annular groove provided on the annular body, the resilient members being arranged to snap-fit into the annular groove, the resilient members being passed through the aperture from one side of the housing to snap-fit into the annular groove, the annular body being located at the other side of the housing.

4. A termination according to claim 1, wherein the resilient mounting means comprise resilient members provided around the aperture, and the retaining means is an annular groove provided on the annular body, the resilient members being arranged to snap-fit into an annular groove provided on the annular body.

A cable termination substantially as described with reference to any one figure of the drawings.

1 12 6. A method of making a cable termination including a cable gland, the method comprising snap-fitting resilient mounting means into retaining means of corresponding dimensions so as to fix the cable gland in an aperture provided in a housing, and, either before or after doing so, securing a cable end in the said gland. 7. A method of making a cable termination substantially as described with reference to any one figure of the drawings.