The invention relates to cable gland assemblies, and particularly
to the earthing of cable gland assemblies. Such assemblies typically provide a
seal and a mechanical and/or an electrical connection between a cable and a wall
through which the cable passes. The invention also relates to an earth tag for
cable gland assemblies.
The EP-A-0587310 discloses a cable gland assembly consisting essentially
of an adaptor, a sleeve, a cap nut and a clamping arrangement. The adaptor and
the sleeve are screwed together with the clamping arrangement effectively held
captive therebetween, and the assembly is intended to be fastened to the wall of,
say, a junction box into which the cable passes. Fastening the assembly involves
inserting the adaptor through a hole in a wall and tightening a nut on the threaded
end of the adaptor after insertion by relative rotation of the assembly and the
The GB-A-2116784 discloses a cable gland earth tag which is fastened
to the cable gland assembly, for instance between the adaptor and the wall through
which the adaptor extends, to provide an earth connection. The tag disclosed essentially
comprises a laminar body having an apertured portion, a part of the assembly being
received in the aperture, and an outwardly extending portion to which an earth
connection is attached. A seal is located in the aperture to prevent fluid entering
the assembly around the tag. In its resting state the seal projects laterally of
the tag. On fastening the assembly at installation, the tag is clamped between
the adaptor and the wall and the seal is compressed so as to be forced radially
of the aperture into sealing contact with the assembly. The clamping on fastening
the assembly also brings the adaptor and the body of the tag into contact thereby
providing an electrical connection from the assembly to earth.
A problem with the earth tags of the type disclosed in GB-A-2116784
is that they 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.
GB 1 382 981 discloses a cable gland assembly according to the preamble
of claim 1. The solution to the above mentioned problem resides in the characterising
part of claim 1.
Preferably, the means for opposing rotation promotes an electrical
connection between the assembly and the tag.
The tag projection may be of any shape or form which enables them
to serve their function of rotation opposing means, and 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. 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.
Additionally preferably, the tag is provided with means for sealing
between the body of the tag and a part or parts of the assembly or the wall. The
sealing means may comprise a sealing ring located in the aperture. The sealing
ring may be provided with means for holding the tag on an assembly part prior
to clamping. The holding means may comprise a plurality of generally curved projections
distributed around the radially inner face of the sealing ring.
The assembly preferably further comprises means for the attachment
of an earthing connection.
The invention will now be described, by way of example, with reference
to the following drawings, in which;
- Figure 1 is a partial cross sectional view of a cable gland assembly according
to an embodiment of the invention; and
- Figure 2 is a perspective view of an earth tag for an assembly according to
With reference to figures 1 and 2, a cable gland assembly indicated
generally at 1 consists essentially of four parts: an adaptor 2, a sleeve 4, a
cap nut 6, all 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
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 is 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 of larger diameter than the entry portion 12. The adaptor 2 has a
multiply 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.
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
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.
The cable C comprises inner conducting wires 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 insulating
sheath 34 which needs to extend only sufficiently into the passageway P to establish
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.
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.
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.
The effect of screwing the sleeve 8 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 figure 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.
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.
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.
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
With reference also to figure 2, an earth tag 200 essentially comprises
a laminar body 202 having an apertured portion 204 and an outwardly extending portion
206. The tag 200 has additional means 218 for connection of earthing means.
The apertured portion 204 has an aperture 208 for receiving a part
of the cable gland assembly 1. Located in the aperture 208, seated against the
cylindrical surface 212 which defines the aperture 208, is a sealing ring 210.
Captivating pips 212, which comprise curved projections, are evenly distributed
around the radially innermost face of the sealing ring 210. Distributed around
the aperture 208, apart from in the region where the apertured portion 204 adjoins
the outwardly extending portion 206, are a plurality of tabs 214 which project
laterally of the tag 200. Each tab 214 is formed by separating a rectangular piece
of the apertured portion 204 on three sides from the remainder of the apertured
portion. Each tab 214 is then bent at its remaining, fourth 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 are alternately bent
so that each tab 214 projects in the oppostite lateral direction to each adjacent
The outwardly extending portion 206 is provided with a hole for receiving
an earthed bolt (not shown) and a shaped part for providing a 'fast-on' earthed
tab as an alternative.
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 pips 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.
On installation of the assembly 1, the earth tag 200 is clamped between
the 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. As
a result of being bent, the tabs 214 are spring loaded and resiliently urged in
the direction of the wall and the flange 14, which 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 coplanar 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 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 maximised 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's edge
interfaces with the flange 14 or wall as appropriate.