Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
~:~719~9
THIS INVENTION relate~ to a cable gland which is '
particularly designed for use with unarmoured electrical cables and,
more particularly, the invention i~ concerned with the provision of a
flame-proof cable gland for effectively ~ealing a cable to a wall of an
5 electrical junction box or the like where it pa~e~ therethrough.
Ela~tomeric grommets and other ~ealant member~ and
materials are generally employed in order to seal effectively an
unarmoured cable to a wall of an electrical junction box or the like
where it passes therethrough.
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However, although such arrangements may be satisfactory for
the most part, they generally do not hold an electrical cable against
axial movement to any degree of certainty and thus cannot be properly
termed flame-proof. ~nil~t they may be flame-proof in their original
aondition, it may occur that the cable will move axially where it passes
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through a wall of an electrical ~unction box and thi~ can cau~e the aeal
to deteriorate or become ineffective. Al~o an axial force on ~uch an
unarmoured electrical cable where longitudlnal movement thereof can
take place can lead to electrical terminals or connectioD~ becoming
5 loosened or in fact broken as a result of axial movement of the cables.
It i~ the object of this invention to provide a cable gland which
can be effectively employed to provide a flame-proof entrance for an
unarmoured cable to an electrical connection box or the like and wherein
axial movement of such a cable i8, at least to a large extent, inhibited
10 or prevented.
In accordance with thi~ invention there is provided a cable gland
comprising a pair of tubular body members defining a paasage for an
electrical cable therethrough, a portion of aaid passageway having an
enlarged internal diameter and receiving within said portion at least one
15 tubular flame-proofing seal adapted to be compressed axially by relative
movement between the two body members to cause the seal to be urged
inwardly into firm contact with the outer sheath of a cable pa~sing
- therethrough in us6, and a deformable clamping ring al~o located within
~aid portion of the pa~age and adapted likewi~e to be compre~sed
20 axially to cause it to clamp radially inwardly onto the outer ~heath of an
electrical cable pasaing therethrough, the cable gland being characteri~ed
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in that the tubular flame-proof~ng ~eal i~ appreciably ~ofter than the
clamping ring to ensure effectlve flame-prooflng of the gland prior
to function of the clamping ring upon movement of the two body parts
towards each other to ~horten the effective length of the said enlarged
5 portion of the passage therethrough.
Further features of the invention provide for the two body parts
to be moveable axially by co-operating screw threads thereon; for an
intermediate axially moveable member to be located within the body
and positioned betwee~ the flame-proofing seal and the clamping ring;
10 for the clamping ring to co-operate with a zone OI decreasing radiu~ at
one end of the part of the passage in which the clamping rlng i~ located,
said zone of decreasing radius serving to wedge the clamping ring
firmly against the outer sheath of a cable in use; and for the clamping
ring to be located on the outer side of the cable gland relative to its
lS means for attachment thereof to an electrical connection box or the like.
Preferably the cable gland embodies said intermediate member
and such intermediate member can have a tubular portion of reduced
external diameter adapted to urge the tubular flame-prooflng seal axially
within it~ location in the passageway and for an enlarged region of the
20 oppo~ite end of said intermediate member to provide ~aid zone of
decreasing radius in the form of a truncated conical shaped surface
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co-operating u~th the clamping ring. The end of the cable gland
which is to be attached to an electrical connection box or the like will
generally have an externally screw threaded spigot portion for passage
through a hole punched in such a connection box- and with v~hich nuts
S can co-operate to firmly secure the cable gland to an electrical
connection box with any required flame-proofing or other seals
po~itioned between the adjacent metal parts.
In its most preferred form the tubular portion of the inter-
mediate member and which is of reduced diameter has an outwardly
10 directed formation at its end adjacent the flame-proofing seal and this
formation, which conveniently takes the form of a flange, co-operates
with a spring clip located partially in a groove in the one body member
to locate the intermediate member captive relative to said body
member. The formation conveniently has a lead-in tapered surface
15 for allowing introduction thereof past the spring clip and ~vherein the
inclined surface operates to flex the spring clip radially outwardly to
allow passage of the formaticn therepa~t but the formation ha~ a planar
surface for co-operation wlth the spring clip on its opposite side 90 that
removal of the intermedlate member is prevented thereby. In thl~
20 manner a ~imple two part a~sembly i~ provided and the simple relative
rotation of the tvro~parts to a d0sired extent brings both the tubular
flame-proofing seal and the clamping ring into operative engagement
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with the outer sheath of an electrical cable pas~ing therethrough.
Clearly the invention is not confined atr~ctly to unarmoured
cable~ but al~o to lengths of armoured cables which have had the
armouring removed therefrom and thereby ~uch ~ections of cables
are in effect unarmoured.
In order that the invention may be more fully understood one
embodiment thereof will now be described with reference to the
accompanying drawings in which :- -
Fig. 1 illu6trates, in partly sectioned longitudinal
elevation, a cable gland according to this invention
in thé inoperative position but wlth a cable pas~ing
therethrough;
Fig. 2 illustrates the same cable gland but in the operative
condition and illustrating the flame-proofing seal
and clamping rlng in the operative condition;
Fig. 3 is a very much enlarged view of a spring clip and
co~perating parts of an intermediate member and
one body membér of the cable gland; and,
Fig. 4 illustrate~ the cable gland in an open condition and
with the part~ not sectioned.
i~71~
As illu~trated, the cable gland in thi~ particular embodiment
of the invention comprise~ a flr~t tubular body member 1 having an
external hexagonal nut configuratlon 2 intermediate it~ end~ snd
whereby the part can be rotated with the aid of a Epanner or the like.
The one end region 3 of the first body part i~ ~crew threaded
externally 80 as to co-operate with a nut ~ whereby the gland can be
~ecured to the wall 5 of an electrical junction box. The hexagonal
formation i~ ~ealed to the esternal surface of the wall by means of a
flame-proof type of sealing washer 6.
The other end region 7 of the first body part is externally
screw threaded and has a larger internal bore than the other end
region 3 80 that two or more tubular elastomeric flame-proof ~eals 8
can be located between the inner wall of this ~ection and the outer
surface of an electrical cable 9 passing through the gland and into the
electrical connection box.
This end reglon 7 oi' the first body part is externally screw
threaded and has, adjacent its end, an internal groove 10 in it~ inner
surface and in which i8 accommodated a spring clip 11 which extellds,
at least over part of its circumferential length, into the bore through
the end portion of the first body part.
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1~7~929
A second body part 12 which 18 internally screw threaded
over the majority of ~ts length to co-operate with the externallg ~crew
threaded end region 7 of the fir~t body part i~ provided to complete the
body. This second body part has an inwardly directed end stop 13 at
5 its end remote from the first body part and houses therein a clamping
ring 14 of elastomeric material and which is located between a suitable
washer 15 and a truncated conical converKent surface 16 on the adjacent
end of an intermediate part 17. The intermediate part 17 has a tubular
portion 18 extending towards and having its free end located within the
10 adjacent end portion 7 of the first body part. The free end of this
tubular portion 18 has an outwardly directed i~ange 19 arranged such
that the tubular portion is maintained within the end portion 7 of the
fir~t body part by co-operation between the spring clip 11 aDd the nat
face 20 of the flange. The end face of the flange is tapered downwardly
15 80 as to provide an inclined bevelled surface 21 ~ich can force the
~pring clip open against its ~nherent resilience when the tubular portion
of the intermedlate member is initially introduced into the end portion
of the first body part. During this the ~pring clip is simply forced back
again~t its resilience and snaps back into a relaxed condition once the
20 flange has pa~ed the spring clip and groove. At this stage, the spring
cl~p only co-operates with the fiat face 20 of the flange and thus the
intermediate member cannot be removed from the fir~t body part except
with e~ctreme difflculty or with special tools.
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This free end of the tubular part of the intermediate member
co-operates wlth the tubular ela~tomeric flame-proof ~eals 8 in use
~o a~ to compress them axially and cau~e radial movement of the
seals inwardly to bear firmly, and in flame-proof manner, agalnst the
5 outer sheath of the cable passing therethrough.
A shoulder 22 i8 formed between the conical surface 16 on the
intermediate member and the tubular portion thereof and this ~houlder
is arranged to abut the end ~urface 23 of the adjacent end portion 7 of
the first body member when the seals have been compressed longi-
10 tudinally to a predetermined and adequate extent.
Only when a predetermined resistance to axial movement of theclamping ring i8 experienced, and this may be designed to be when the
shoulder contacts the end 23 or, alternatively, when sufficient torque
i~ required to rotate the second body part relative to the first body part,
15 i8 the clamping ring forced into the truncated conical surface 80 as to be
urged radially toward~ the outer sheath of the cable 9. Further rotation
of the two body parts relative to each other cawes further movement of
the clamping ring into engagement with the outer ~urface of the cable
until, when a predetermined torque i~ applied between the two body part~,
20 the clamp~ng ring i~ firmly and sufficiently in contact ~vith the outer
surface of the cable. At thi~ stage the clamping ring will actually be
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1~719;~9
"bit~ng" into the outer sheath of the cable and, due to lts ~ubstan-
tially greater hardness than the flame-proof seals, will adequately
locate the cable against axlal movement thereof. It wlll be under~tood
that the inventlon only applles to cable~ which have sufficient tensile
5 ~trength to enable the outer sheath to be clamped In this manner and
the types of cables vwhich do not have such adequate strength must be
provided for in totally different manner.
- It will be understood that after a cable has passed through
the passageway in the cable gland the two body part~ can be relatively
10 rotated to effectively shorten the length of the portion of enlarged
diameter of the passageway through the body and in v,~hich the flame-
proof seal~, intermediate member, and ¢lamplng ring are lobated.
Initially the flame-proof seals will engage the outer sheath of the cable
and when sufficient resistanoe to further axial compression is
15 experienced which, as indicated above may take place when the ~houlder
abuts the end of the flrst body part, the clamping ring v/ill be urged into
the conical shaped ~urface of the intermediate member and thus clamp
the cable ~heath firmly relative to the cablè gland. A predetermlned
torque will be required which may be accurately measured or assessed
20 by mean~ of the general dimens~on of tools conventioDally wed for
tlghtening such a gland. At such a torque the cable will be flrmly
anchored against axial movement to a predetermined extent.
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A lock nut 24 can be provided on the external screw
threaded surface of the fir~t body part in order to lock the second
body part relattve thereto In the final relative positions of the two
body Rarts.
It will be under~tood that for the effective operation of the
above described cable gland the hardnesses of the flame-proof seals
and the clamping ring must be chosen properly. It ha~ been found
that effective flame-proof sealing i~ achieved when an elastomeric
seal having a Shore hardne~ of from 50 to 80 and, preferably, from
55 to 65 is employed and a clamping ring having a Shore hardne~s of
from about 70 to 95 and preferably from 85 to 95 are employed. In
either event it is required that the Shore hardness of the flame-
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proofing seals be appreciably less than that of the clamping ring to
ensure that the flame-proofing seal is rendered operative f{rst.
In either event it is preferred Shat the Shore hardness of the
cla~mping ring be at least 20 greater than that of the flame-proofing
seal and preferably about 30.
.
It ~vlll be understood that the general situation {~ that effective
flame-prooflng requlres a sub~tantially softer ela~tomerlc material
~ which allow~ the outer sheath to creep when {t i~ placed under a ten~ile
.
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'719Z9
force. It i8 for thia reason that a ~eparate clamping ring iB employed
which, although it can be of elastomeric materlal, can be sufficiently
hard to effectively eliminate creep a~ a re~ult of ten~ile force being
applied to the cable at least to a predetermined extent and within certain
5 acceptable limitations. However, such a clamping ring may not have
desirable flame-prooflng characteristics.
It will be understood that numerous variations may be made to
the above described embodiment of the invention without departing
from the scope hereof. In particular the conical eurface on the inter-
10 mediate element may be replaced by one on the oppoaing end of the~econd body part and, in fact, the entire intermediate member could
be absent. In such a case the internal dimension~ of the two body part~
must be arranged ~uch that effective compression of the flame-proofing
seal~ and the clamping ring can be achieved without the danger that
15 either -will not operate effectively.
The invention therefore provides a simple yet effective gland
for flame-proofing the positioDs where cables enter an electrical
junctlon box or the llke and wherein the cables themselves haqe
sufficient inherent teneile strength to enable the outer sheath thereof
20 to be employed to resist tearing of the cable out of the cable g~and.
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