CABLE GLANDS

Abstract: A cable gland for use with cables (1) having armour (3) of widely differing thickness comprises a body (5) and a gland nut (7) threaded to the body (5) which together enclose an armour grip (9) comprising an armour cone (10) having a male frustoconical surface co-operating with a female frustoconical surface on an armour ring (11). The frustoconical surfaces have substantially equal semiangles in the range 12-20 DEG and the armour ring (11) and the armour cone (10) are urged together by a mechanism independent of and contained within the gland nut (7). The larger-than-normal semiangle allows the whole range of armour thicknesses to be accommodated by the same gripping components without requiring undue length, and the separated mechanism overcomes side effect that the cone grip is not self-locking. Preferred mechanisms also improve perfomance in deluge tests.

Description: Cable Glanas This invention relates to cable glands, and more especially to glands for electric (and/or optical) cables having a metallic protective layer (hereinafter for simplicity called "armour") of wires, tape, or braid. Such armour needs to be mechanically secured and electrically earthed in the glands used to terminate the cable, and this is almost always done by gripping the armour between male and female frustoconical surfaces on members (respectively known as the armour cone and armour ring) that are urged axially towards each other by the action of at least one additional screw-threaded member when the gland is assembled. By using a cone semi-angle in the approximate range 6 - 9 ° , a self-locking effect is obtained, in that the armour is not released if the gland is subsequently unscrewed. However, the different types of armour have very different radial thicknesses, and if the same armour ring were used for all types of armour, the gland would need to be very long to accomodate the difference m axial position of the armour ring between the thinnest and thickest armours, with penalties in both material cost and space requiremen . It has been the conventional practice to use different armour rings, depending on the type of armour, with the result that stock-holding is high and there may be a risk of the wrong ring being used and an inadequate grip obtained. One manufacturer has introduced a gland design in which a single armour ring has frustoconical surfaces of two different diameters at its opposite ends, and so can be reversed to grip different types of armour,- but it is difficult to know whether the ring is the right way round at the time of assembly (even if access and lighting conditions are favourable) and almost impossible to check it afterwards. In accordance with the present invention, a cable gland for use with cables having armour of widely differing thickness comprises a body and a gland nut threaded to the body which together enclose an armour grip comprising an armour cone having a male frustoconical surface co-operating with a female frustoconical surface on an armour ring and is characterised by the said frustoconical surfaces having substantially equal se iangles in the range 14-20° and the armour ring and the armour cone being urged together by a mechanism independent of and contained within the gland nut. In some cases the armour cone may be an integral (monolithic) projection of the gland body. The gland body may enclose an inner seal for engaging an inner sheath or bedding layer beneath the armour of the cable and/or the gland nut may enclose an outer seal for engaging an outer sheath (or oversheath) surrounding the armour. Preferably the said semiangle is in the range 14-18 . By using such a large semi-angle, the length of relative longitudinal movement required to accomodate differences in thickness of different armour types is anagable, and the independent mechanism urging the armour cone and armour ring together overcomes the loss of self-locking action and makes intentional dis-assembly easier. Preferably the mechanism for urging the armour cone and the armour ring together is a direct screw-threaded connection between the armour ring and the body, or between the armour ring an the armour cone; alternatively a separate driver member screwed to the body or cone may be used. When the ring or the driver member is directly threaded to the body, it has the advantage that the performance of the gland in "deluge" tests is improved and in some cases an external deluge seal (which is vulnerable to damage; can be dispensed with. When the gland includes an outer seal, the armour ring or driver member, as applicable, preferably extends to and engages that seal. In many cases, the armour can be adequately gripped by screwing the armour ring "finger tight", but preferably the armour ring or the driver member is provided with a suitable formation for engagement with a spanner, wrench or other tool. This may, for example, be a pair (or more than one pair) of flats, one or more than one bore, or simply a knurled gripping surface. The invention will be further described, by way of example, with reference to the accompanying drawings in which each figure is a longitudinal cross-section of one form of cable termination in accordance with the invention. The termination of Figu e 1 is made on a cable 1 having an inner sheath 2, armour 3 and an outer sheath 4 and includes a gland comprising a body 5 enclosing an inner seal 6, a gland nut 7 in screw-threaded engagement with the body 5 and enclosing an outer seal 8, and an armour grip 9. The body, gland nut and outer seal are broadly conventional in design, and the inner seal 6 is more fully described in another application filed on the same day as this application claiming the priority of GB9424684.0 filed 7 December 1995 (07.12.95) . The armour grip comprises an armour cone 10 and an armour ring 11. The cone 10 is contained by the gland body 5, since a shoulder 12 in the body, acting via the inner seal 6, limits the movement of the cone to the right as drawn, that is in the direction away from its apex. The semiangle « of the cone is about 17.0°. The armour ring 11 has a matching semiangle and is urged towards the cone 10 by direct screw-threaded engagement with the gland body 5. The ring 11 has an extension with a peripheral surface 13 that is knurled to facilitate tightening of the screw thread by hand or by the 5 use of a friction-grip wrench (alternatively, or in addition, it may have a pair of flats for engagement with a spanner) , and it is long enough to reach and be sealed by the outer seal 8. Because the cone semiangle is large, the difference in 10 the relative axial positions when the gland is tightened on different thicknesses of armour is substantially less than for conventional armour grips with conventional cone angles in the 6-9° range - typically in the region of half the difference. For example, in a particular size of gland with a semiangle of 15 17°, an armour ring with an internal diameter at its narrow end of 18.1mm and fitting within an ISO M26 screw thread, and an armour cone having an external diameter of 24mm at its wide end and a bore cf 14.5mm, the difference in relative axial positions when the gland is tightened on a steel tape armour 0 with a nominal radial thickness of 0.15mm or on a single wire armour with a nominal radial thickness of 3.15mm is no more than 4.3mm (compared with about 9.7mm if the cone angle were a conventional 6°) . Because the screw threads between the body and the armour 5 ring and the body and the gland nut are in series (and the ring is sealed to the nut by the outer seal) , the gland passes the ERA Technology Ltd/Shell deluge test DT SOI;1991 for offshore cable glands without requiring an external deluge seal. 0 To make up the termination," the cable end is prepared ("cut back") in an entirely conventional manner and the gland nut 7 and armour ring 11 unscrewed and slid over the cable end (together with the outer seal 3) . The cable end is then inserted through the body cf the gland, and through the inner seal and armour cone within it, and the end of the armour 3 positioned radially between the armour cone and the body (or with some types of armour, it may be preferable to separate the cone from the body and insert it under the armour in a preliminary step) . The armour ring 11 is threaded into the body and tightened by hand, finishing with a slight turn with a wrench if preferred, and the gland nut screwed onto the body and tightened to complete the termination. Since the armour grip is independent of the gland nut 7, the latter can be unscrewed for visual inspection and/or mechanical testing, without risk of the cable end becoming displaced. Figure 2 shows a modification in which the armour ring 14 is a simple collet secured in place by a separate driver member 15 directly threaded in the body 5. Figure 3 shows a further modification in which the driver member 16 is threaded on, instead of n, the body 5; the spacer 17 may be integral (monolithic) with the driver member or it may (as drawn) be separate; in the latter case it may be of hard plastics material if desired and may be bonded to the driver member (or to the outer seal, if preferred) to reduce the number cf components to be positioned.

Claims: CLAIMS 1 A cable gland fcr use with cables having armour of widely differing thickness comprising a body and a gland nut threaded to the body which together enclose an armour grip comprising an armour cone having a male frustoconical surface co-operating with a female frustoconical surface on an armour ring characterised by the said frustoconical surfaces having substantially equal semiangles in the range 12-20° and the armour ring and the armour cone being urged together by a mechanism independent of and contained within the gland nut. 2 A cable gland as claimed in claim 1 in which the armour cone is an integral (monolithic) projection of the gland body. 3 A cable as claimed in claim 1 or claim 2 in which the said semiangle is in the range 14-18 . 4 A cable gland as claimed in any one of claims 1-3 in which the mechanism for urging the armour cone and the armour ring together is a direct screw-threaded connection between the armcur ring and the body, or between the armour ring and the armour cone. 5 A cable gland as claimed in any one of claims 1-3 in which a separate driver member screwed to the body or cone is used for urging the armour cone and the armour ring together. 6 A cable gland as claimed in any one of claims 1-5 in which the gland body encloses an inner seal for engaging an inner sheath or bedding layer beneath the armour of the cable. 7 A cable gland as claimed in claim 6 in which the said inner seal is as claimed in any one of claims 1-12 of our application no. filed on the same day as this application. 8 A cable gland as claimed in any one of claims 1-7 in which the σland nut encloses an outer seal for engaging an outer sheath (or oversheath) surrounding the armour of the cable. 9 A cable gland as claimed in claim 4 in which the gland nut encloses an outer seal for engaging an outer sheath (or oversheath) surrounding the armour of the cable and the armour ring extends to and engages that seal. 10 A cable gland as claimed in claim 5 in which the gland nut encloses an outer seal for engaging an outer sheath (or oversheath) surrounding the armour of the cable and the driver member extends to and engages that seal. 11 A cable gland as claimed in claim 4 or claim 9 in which the armour ring is provided with a formation for engagement with a spanner, wrench or other tool. 12 A cable gland as claimed in claim 5 or claim 10 in which the driver member is provided with a formation for engagement with a spanner, wrench or other tool. 13 A cable termination made with the gland claimed in any one of claims 1-12. 14 A cable installation made with the gland claimed in any one of claims 1-12.

Inventors: DOUBLEDAY THOMAS, FRIAR ALAN, DOUBLEDAY, THOMAS, FRIAR, ALAN
Applicants: BICC PLC, DOUBLEDAY THOMAS, FRIAR ALAN, BICC PUBLIC LIMITED COMPANY, DOUBLEDAY, THOMAS, FRIAR, ALAN
Application year: 1995
Main classification: H02G15
IPC codes: H02G15