SPECIFICATIONCable connectionsThis invention relates to cable glands and to electrical connectors including such glands.
The risk of damage to electrical cables in mines and other rough working environments can be very great. For example, in coal mines cables for feeding electrical supplies to the coal face to operate equipment, such as lighting equipment, are very vulnerable to crushing or severing by rock falls, or by the actions of men or machinery anywhere aiong the length of the cables. The severing of a cable carrying a lighting supply to the coal face could obviously be extremely dangerous.
The relatively well-lit working area would suddenly be plunged into darkness.
In order to reduce the risk of damage to cables, they must be protected by a metal reinforcing layer. This layer presents considerable problems during the installation of the cable runs, and in subsequent changing of the runs. At cable terminations and junctions the reinforcing layer has to be properly made off.
The cables are also frequently being hauled about-and are subjected to extremely rough treatment, and it is necessary to ensure that, throughout their length, the cables can withstand the tensile forces applied to them. It would be no use installing a reinforced cable to withstand the hazardous conditions and then joining or terminating the cable in such a way that the conductors of the cable can become subjected to these forces.
It is desirable that any cable termination provided for use can be quickly and easily assembled in the very difficult working conditions existing in a mine.
A very suitable type of cable for use in mine lighting installations is that of the "signal pull wire cable" type comprising a plurality of electrical conductors each of, say, 1 6 strands of 0.2mm diameter copper wire, each core being insulated with its individual sleeve or p.v.c. or other insulating material. The conductors are protected by a reinforcing sheath of interwoven brasscoated steel wires formed as an open-mesh braiding extending along the length of the conductors. The braiding is embedded in a layer of p.v.c., or other insulating material, which surrounds the insulated conductors.
It is an object of the present invention to provide a cable gland which is suitable for a reinforced cable, particularly, but not exclusively, a cable of the above type, and which will provide a mechanically strong interconnection between the reinforcing layer and the equipment or cable extension to which the cable is connected, so that the tensile forces normally encountered in the proper use of such cable will not damage the conductors.
According to the invention, a cable gland comprises a sleeve having an annular flange and cylindrical first and second portions at opposite ends of the flange, the sleeve having a bore extending axially through the first portion, the flange and the second portion to receive a cable having a metal reinforcing layer; a ferrule to encircle at least part of the length of the first sleeve portion, which ferrule in use is forced over the end of the cable metal reinforcing layer whichis doubled back over said first sleeve portion so that the end of the reinforcing layer is trapped between the outer surface of the first sleeve portion and the inner surface of the ferrule; a cylindrical bush having a first externally-threaded portion for attachment to a body to which the cable is to be attached, a second externallythreaded portion and an axial bore to receive the ferrule with the end of the second externallythreaded portion abutting the flange of the sleeve; and a nut having an inwardly extending annular flange to encircle the second sleeve portion and to abut the flange of the sleeve and having a threaded portion engageable with the externallythreaded portion of the bush to clamp the bush and the sleeve together.
Preferably the bush has a hexagonal flange extending outwards between the first and second externally-threaded portions to faciiitate screwing of the bush into the body.
A cable connector can comprise two glands as defined above having their bushes screwed intorespective opposite ends of a tubular body andmeans within the tubular body interconnecting the conductors of two cables extending through therespective glands.
Embodiments of the invention will now bedescribed, by way of example, with reference tothe accompanying drawings, in which:Fig. 1 is a sectional view of a cable gland inaccordance with the invention, assembled on areinforced cable,Fig. 2 is an exploded view of the components of the gland,Fig. 3 is a sectional view of a cable connectorincorporating two of the glands,Fig. 4 is a pictorial view of a strain-preventinghook for a cable connector part, andFig. 5 is a plan view of the hook of Fig. 4assembled to a cable and a cable connector part.
Referring to Figs. 1 and 2 of the drawings, acable gland 1 comprises a sleeve 2 which fits over the outside of a reinforced cable 3. The borewhich receives the cable is tapered to facilitareinsertion of the cable. In order to centralise and seal the cable 3 in the bore of the sleeve 2, some turns of an adhesive insulating tape 19, such asp.v.c. tape, are wound round the cable, the turnsoverlapping so that the thickness of the tape massincreases with distance away from the gland end of the cable. This tape is forced into the opening of the bore in the sleeve 2. The sleeve 2 comprises three integral parts, namely a front cylindrical portion 4, an annular flange 5 and a rear cylindrical portion 6.
A metal reinforcement braiding 7 is cut to a suitable length and is doubled back over the portion 4. A ferrule 8, having an inwardly-turned end flange 9, is forced over the braiding 7 until the flange 9 abuts against the bend in the braiding.
The braiding is therefore firmly gripped between the ferrule and the sleeve portion 4. An O-ring 10 forms a seal between the end of the ferrule 8 and the flange 5.
A bush 11 has an externally-threaded end portion 12 for screwing into a member 13 whichmay be, for example, an equipment casing.
Alternatively, the portion 12 may extend through a clearance hole in the member 13 and be secured by a nut (not shown). A hexagonal flange 14 facilitates the screwing-in of the portion 12. An 0ring 15 forms a seal between the flange 14 and the body 1 3. The bush 11 also has an opposite end portion 1 6 which is externally-threaded. This bush has an axial bore so that it fits over the ferrule 8 and the portion 4 of the sleeve 2, with the end of the bush abutting the flange 5 and sealing with the O-ring 10.
A gland nut 17 fits over the portion 6 of the sleeve 2 in engagement with the flange 5 and screws on to the threaded portion 16 of the bush 11, so that the bush and the sleeve are firmly clamped together.
Free ends of the cable conductors 1 8 are connected, as required, to electrical equipment within the casing 13.
With a particular cable it has been found that a force of at least 400 Ibs. can be applied between the body 13 and the cable 3, in a direction tending to pull the cable out of the gland, without any axial displacement taking place between the cable and the gland. This is due to the firm anchoring of the braiding 7 in the gland.
The cable with the sleeve 2, the ferrule 8 and the nut 1 7 attached thereto can be initially free of the bush 1 so that any twists can be removed from the cable. The end of the cable can then be inserted into the bush which is already attached to the body 13, and the nut 1 7 can be tightened without introducing any twists into the cable.
Alternatively, the bush 11 could be attached loosely to the rest of the gland, and could then be screwed into the body 1 3 without causing twisting of the cable since the bush turns freely on the ferrule, the nut 17 being finally tightened on to the bush to secure the cable.
Referring now to Fig. 3 of the drawings, a connection between two cables 1 9 and 20 can readily be made by firstly screwing a gland 1 as described above into one end of a tubular body 21 to retain the cable 19. The body 21 may have flats (not shown) formed on its periphery to receive a spanner to facilitate tightening of the gland boss into the body. The end of the body 21 has a chamfer 22 on its inner edge to seal with the gland O-ring 1 5.
The insulated conductors 1 8 of the cable 1 9, here conveniently shown as a single pair of conductors, are long enough to extend right through the body 21 and to emerge from the other end of the body. A connector part 22 preferably has one male and one female connection 23 and 24, respectively, which are attached by screws to the bared end of the conductors 18, either before or after passing the conductors through the body 21.
The cable 20 is attached to its gland 25, and a connector part 26, complementary to the connector part 22, is connected to the conductors 27 of the cable 20. The connector parts 22 and 26 are then mated outside the body 21 and the compiete connector is pushed into the body, the conductors 1 8 curling up within the body. The gland 25 is then offered-up to the open end of the body 21 and the screwed connection is made between the bush and the body or, if the bush has already been inserted, simply between the nut and the bush, as previously described.
The clamping of the cable 20 does not need to cause any twisting of the cable, so the connector parts 22 and 26 remain properly interconnected, the wad of curled-up conductors 1 8 tending to urge the connector parts together. Furthermore, some twisting of the cable in the gland is possible without damaging or disconnecting the connector parts.
This provides a very simple method of interconnecting cables without the need for soldering or crimping the connections or filling the joint with a sealing compound. The resulting joint is mechanically very strong and can withstand large tensile forces as explained previously.
The cables to be interconnected will normally be taken to the site with the connector parts already connected to the cable conductors. Unless provision is made to prevent it, there would be considerable risk of the connector parts being pulled off the conductors and/or the conductors being broken off, even before the cables reached the site. Hence, in order to prevent strain being applied to the conductor ends, a strain-preventing hook may be used, as shown in Figs. 4 and 5. The hook 30 comprises a slotted portion 31 integral with a block 32. The block 32 has two transverse holes 33 and 34 threthrough, the hole 33 lying in a plane including the centre-line of the hook 30 and the hole 34 lying below that plane.
A connector part 35 is somewhat similar to the parts 22 and 23 of Fig. 3 but has a central web 36 interconnecting the insulating blocks 37 and 38 which contain the male and female connections 39 and 40, respectively. The web 36 is shorter and thinner than the blocks 37 and 38, and the slotted portion 31 of the hook fits over the web and between the blocks 37 and 38.
In use of the hook, the cable conductors 1 8 are passed in opposite directions through the respective holes 33 and 34 and their bared ends are attached to the connections 39 and 40 by set screws in the usual manner, the hook being, at this stage, separate from the connector part. The slotted portion 31 is then hooked over the web 36 and the conductors 1 8 are drawn back through the holes 33 and 34 until there remains only a small amount of slack in the conductors adjacent the connections. This retains the hook in position relative to the web 36, and any pull which is applied to the connector part, which would otherwise tend to pull the connector off the cable conductors, is applied to the sections of the conductors within the holes 33 and 34 and hence to the sections of the conductors further up the cable away from the connector part 35. No pull is applied to the conductor end portions between the block 32 and the connections 39 and 40. The disposition of the holes 33 and 34 relative to the centre of the hook 30 minimises any tendency for the hook to disengage from the web 36.
Connector blocks of the kind used for the part 35 are well-known in the electrical art.
Many other applications of the cable gland can, of course, be envisaged. For example, any number of reinforced cables may be fed to the interior of a junction box via respective glands located in respective apertures in the walls of the box.