Patent Publication Number: US-2003226680-A1

Title: Cable gland assemblies

Description:
TECHNICAL FIELD OF THE INVENTION  
       [0001] The invention relates to cable gland assemblies, and particularly to the earthing of cable gland assemblies. The invention also relates to an earth tag for cable gland assemblies.  
       BACKGROUND OF THE INVENTION  
       [0002] Cable gland assemblies typically provide a seal and a mechanical and/or an electrical connection between a cable and a wall through which the cable passes. A cable gland assembly may comprise a seal, which is clamped between an adaptor and the wall, so that the seal is forced radially of an aperture into sealing contact with the assembly. The clamping on fastening the assembly may also bring the adaptor into contact with a tag, thereby providing an electrical connection from the assembly to earth.  
       [0003] A problem with cable gland assemblies of this type is that the tag may be urged to rotate on fastening the assembly as a result of the relative rotating motion which is involved. The rotation of the tag may result in its misplacement and hinder its installation, not least because several assemblies are often installed in close proximity and the tag needs to maintain its position in order not to interfere with other, adjacent assemblies and for easy attachment of an earth connection.  
       SUMMARY OF THE INVENTION  
       [0004] Disclosed herein is a cable gland assembly comprising parts providing a mechanical and/or electrical connection between a cable and a wall, and a tag which is fastened by clamping between a part of the assembly and another part of the assembly or the wall thereby to provide a connection to earth from the assembly, wherein the tag comprises a means for opposing rotation of the tag about a part of the assembly during clamping. 
     
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
     [0005] For a more complete understanding of the present invention and the advantages thereof, reference is now made to the following description taken in conjunction with the accompanying drawings, in which:  
     [0006]FIG. 1 is a partial cross sectional view of a cable gland assembly according to an embodiment of the invention; and  
     [0007]FIG. 2 is a perspective view of an earth tag for an assembly according to the invention. 
    
    
     DETAILED DESCRIPTION  
     [0008] With reference to FIG. 1, a cable gland assembly indicated generally at  1  consists essentially of four parts: an adaptor  2 , a sleeve  4 , a cap nut  6 , all preferably made from brass, and a clamping arrangement  8 . The four generally cylindrical parts  2 ,  4 ,  6 ,  8  together define a central passageway P for a cable C and are preferably formed of a conducting material such as a metal, preferably being brass.  
     [0009] The adaptor  2  has a radially extending flange  14  which is partly hexagonally shaped for a spanner. To one side of the flange  14  the adaptor  2  has an externally threaded entry portion  12  for insertion through a hole in the wall of, say, a junction box (not shown). The adaptor  2  may be fastened to the wall with a nut (not shown) screwed on to the entry portion  12  after insertion. To the other side of the flange  14 , the adaptor  2  has an externally threaded attachment portion  16 , which is preferably of larger diameter than the entry portion  12 . The adaptor  2  has a multiple-stepped bore  42 , which gradually decreases in diameter towards the entry portion end, and the step nearest the attachment portion end provides a shoulder  44 . A rubber diaphragm seal  61  with a central opening  62  capable of expanding to accommodate various different diameters of cable has an annular retaining ring  64  which is seated against the shoulder  44 .  
     [0010] The sleeve  4  has at one end an internal thread  18  for engagement with the thread on the attachment portion  16  of the adaptor  2 . At its opposite end  20 , the sleeve  4  is externally threaded to receive the cap nut  6 . The sleeve  4  has a bore  46  with a step approximately at its midpoint which provides a shoulder  48 .  
     [0011] The clamping arrangement  8  comprises first and second clamping parts  19 ,  21 , which together define a cable armour clamping gap  22  therebetween. Extending into the gap  22  from an annular recess  24  in the first clamping part is cable armour engaging means  26 .  
     [0012] The cable C comprises inner conducting wires (not shown) surrounded sequentially by an inner insulating sheath  30 , armour wires  32  and an outer insulating sheath  34 . The armour wires  32  are exposed as a result of the stripping back of the outer insulating sheath  34 , which needs to extend only sufficiently into the passageway P to establish a seal.  
     [0013] The first clamping part  19  is constituted by a spigot having a central bore  36  of a size greater than the diameter of the cable C in the region where it has been stripped back. The spigot  19  is divided by a radially extending flange  50  into a clamping portion  52  of frusto-conical shape and a substantially cylindrical sealing portion  54 , which is a close tolerance fit in the retaining ring  64  of the seal  61 .  
     [0014] The second clamping part  21  is constituted by a clamping ring having a cylindrical outer surface  58  and a central bore, which is tapered in a manner complimentary to the shape of the clamping portion  52  of the spigot  19 , but of larger diameter. As a result, when the spigot  19  and the clamping ring  56  are fitted together, the interior surface  60  of the clamping ring  21  and the exterior surface of the clamping portion  52  have a substantially parallel relationship. The clamping ring  21  is a close tolerance fit in the bore  46  of the sleeve  4 , abutting against the shoulder  48 .  
     [0015] The cable armour clamping means  26  is constituted by a resiliently compliant split, metal o-ring received in the annular recess  24 . In its normal state, the o-ring  26  is of such a diameter that it will extend out of the recess  24  and into the gap  22 , but is capable of complying, that is, compressing, in terms of its diameter decreasing, to the extent that it can recede completely into the recess  24  and no part of it any longer extends into the gap  22 . The o-ring  26  is resilient in that its reaction to compression is to attempt to return to its normal state diameter.  
     [0016] The effect of screwing the sleeve  4  and the adaptor  2  together is to urge the clamping ring  21  axially towards the spigot  19  thereby to close the clamping gap  22  and to clamp the armour wires  32  between the spigot  19  and the clamping ring  21 . The split o-ring  26  will compress according to the thickness of the wires  32 , and its reaction to compressing will be to exert a clamping force on the wires  32 . The wires  32  may be of such a thickness that a suitable clamping gap is attained before the axially forward end of the clamping ring  21  reaches the flange  50  of the spigot  19 , in which case the o-ring  26  will comply to the extent of receding completely into the recess  24 . On the other hand, and as specifically shown in FIG. 1, the wires  32  may be thinner than even the minimum clamping gap attainable (determined by the relative dimensions of the spigot  19  and the clamping ring  21 ), in which case, the o-ring  26  is compressed only sufficiently to permit the accommodation of the wire  32 , and the reaction force the o-ring  26  exerts clamps the wires  32  against the clamping ring  21 .  
     [0017] An annular seal  66  is disposed between the cap nut  6  and the sleeve  4 , and the effect of screwing the cap nut  6  on to the sleeve  4  is to radially compress the seal  66  against the cable C.  
     [0018] Fixed to the outer surface of the cap nut  6 , with high performance adhesive, is a generally disc-shaped transponder  100 . Suitable transponders are manufactured by the AEG company under their designations ID300 and ID700. The transponder  100  has an information storage facility (not shown) for storing information, such as a unique identity code for the assembly, data relevant to its last inspection, etc. Typically, the transponder  100  is capable of storing eighty bits of information. The information may be read from the storage facility.  
     [0019] The information storage facility of the transponder  100  is divided into two portions. A first portion containing a unique code for the assembly  1  including identification of its type, model number, cable size acceptance, certification references (that is, the standards which it is certified to fulfil) and performance limits. This information is hand written into the first portion at about the time the transponder  100  is incorporated into the assembly and may not easily be erased or altered, at least, not in the field. The second portion of the storage facility is field programmable to facilitate the storage in the memory of information such as inspection status, last inspection date and site reference, which needs to be updated periodically.  
     [0020] With reference also to FIG. 2, an earth tag  200  preferably comprises a substantially laminar body  202  having an apertured portion  204  and an outwardly extending portion  206 . The apertured portion  204  preferably has an aperture  208  for receiving a part of the cable gland assembly  1 .  
     [0021] Additionally, the tag preferably comprises a means for sealing between the body of the tag and a part or parts of the assembly or the wall. The sealing means preferably comprise a sealing ring  210  located in the aperture  208 . The sealing ring  210  may be provided with means for holding the tag on an assembly part prior to clamping. The holding means preferably comprise a plurality of captivating protrusions  212  distributed around the radially inner face of the sealing ring. The sealing means preferably lie radially inwardly of the means for opposing rotation. Thus, on clamping, the means for opposing rotation do not cut or impair the sealing action of the sealing means. The sealing means may be a separate shaped seal ring  212  inserted into or about the tag aperture or may be moulded thereabout so as to be bonded to the tag aperture. The assembly preferably further comprises means for the attachment of an earthing connection.  
     [0022] The tag  200  preferably comprises a means for opposing rotation about a part of the assembly during clamping. The means for opposing rotation preferably comprises one or more tabs  214  distributed around the aperture. Preferably, a plurality of tabs  214  are distributed around the apertured portion  204 , except the region where the apertured portion  204  adjoins the outwardly extending portion  206 .  
     [0023] Each tab  214  is preferably formed by separating a rectangular piece of the apertured portion  204  on three sides from the remainder of the apertured portion  204 . Alternatively, the tabs  214  may be other shapes such as triangular, or any other shape which enables them to serve their purpose of opposing rotation of the tag  200 . Each tab  214  is then preferably bent at its remaining, uncut side, so as to be inclined at an angle with respect to the remainder of the body of the apertured portion  204  and to project laterally of the tag  200 . The tabs  214  preferably are alternately bent, so that each tab  214  projects in the opposite lateral direction to each adjacent tab  214 . Alternatively, the tabs may be configured and bent so as to extend radially with respect to the apertured portion  204 .  
     [0024] The projections may be resiliently urged away from the tag, for instance spring loaded, or made from a compressible material whether resiliently compressible or not. Preferably, each projection comprises a tab-like piece of the tag body, which is angled to project laterally of the tag. Further preferably, each tab-like piece is resiliently urged laterally of the tag. The tag may be provided with means for holding the tag on an assembly part prior to clamping.  
     [0025] The outwardly extending portion  206  is preferably provided with a hole  216  for receiving an earthed bolt (not shown) and a shaped part  218  for providing a ‘fast-on’ earthed tab as an alternative.  
     [0026] The cable gland assembly  1  is supplied with the earth tag pre-installed. That is to say, the insertion portion  12  of the adaptor  2  is inserted through the aperture  208 , and the captivating protrusions  212 , which are sized to engage the insertion portion  12 , hold the tag  200  on the assembly  1  and prevent it from sliding off the adaptor  2  prior to installation of the assembly  1 .  
     [0027] On installation of the assembly  1 , the earth tag  200  is preferably clamped between a wall (not shown), through which the insertion portion  12  is inserted, and the flange  14 . On tightening the assembly  1 , which, as aforementioned, involves screwing together the assembly  1  and a nut on the remote side of the wall, the tag  200  is squeezed between the wall and the flange  14 , respectively. The first parts of the tag  200  to contact the wall and the flange  14 , respectively, are the tabs  214 .  
     [0028] As a result of being bent, the tabs  214  are preferably resiliently urged in the direction of the wall and the flange  14 , which preferably promotes a good electrical connection between the wall, the assembly  1  and the tag  200 . However, because the urging is resilient in nature, further tightening of the assembly simply forces the tabs  214  back towards a position at which they are co-planar with the remainder of the body of the tag  200 . Tightening the assembly  1  also causes the sealing ring  210  to perform in the manner described in GB-A-2116784, the complete content of which is incorporated herein by reference.  
     [0029] The relative rotating motion involved in fastening the assembly  1  to the wall tends to urge the tag  200  to rotate. However, the contact between the tabs  214  and the wall and the flange  14 , respectively, generates frictional forces which oppose the tendency to rotate, hence the tag  200  maintains its position. The frictional forces are maximized by arranging each tab with its longitudinal axis, that is the axis extending through the bent side and the opposite side, tangential to the aperture, so that the full length of the opposite side&#39;s edge interfaces with the flange  14  or wall, as appropriate.  
     [0030] The tag  200  of the cable gland assembly  1  may provide a single item which fulfils the functions of: providing an efficient earth for the assembly due to the means for opposing rotations; providing a fluid seal between the gland assembly and the wall aperture, for example, through which it passes; and, providing means to prevent rotation of the tag and ensure correct positioning. The means for preventing rotation of the tag may also fulfil the function of a so-called ‘shake-proof’ washer, keeping the gland assembly tightly clamped together and guarding against loosening of the assembly due to vibration, for example. Thus, additional shake-proof washers are not needed, making the gland assembly simpler and more compact.  
     [0031] Having thus described the present invention by reference to certain of its preferred embodiments, it is noted that the embodiments disclosed are illustrative rather than limiting in nature and that a wide range of variations, modifications, changes, and substitutions are contemplated in the foregoing disclosure and, in some instances, some features of the present invention may be employed without a corresponding use of the other features. Many such variations and modifications may be considered obvious and desirable by those skilled in the art based upon a review of the foregoing description of preferred embodiments. Accordingly, it is appropriate that the appended claims be construed broadly and in a manner consistent with the scope of the invention.