Note: Descriptions are shown in the official language in which they were submitted.
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CONNECTOR FOR CORRUGAT~D-METAL-
SHEATHED ELECTRI~ CABLES
This invention relates to a connector for corru-
gated-metal-sheathed electric cables.
In the electric cable art, it is known to manu-
facture cables having metallic sheaths which are provided
with helical corrugations. The sheath is usually made of
an extruded or a longitudinally welded metal tube which is
corrugated by a revolving tool, or set of tools which de-
forms the tube so as to produce a continuous helical groove,
or trough defined by adjacent convolutions of a continuous
helical ridge, or crest. In some embodiments, the groove is
provided with a flat bottom from each side of which extends
upwardly an arcuate ridge and, in other embodiments, the
surface of the cable, when viewed along the line parallel to
the longitudinal axis of the cable, is somewhat sinusoidal
in configuration.
It is also known in the electric ca~le art to vary
sign'ficantly the depth of the corrugation of any given size
of sheath in oder to accommodate a wider range of diameters
of cable core t~an an acceptable range of clearance between
the core and sheath permits. Such variations in corrugation
depth result in significant variations in the outer diameter
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of the corrugated tube, that is to say a greater corruga-
tion depth will result in a larger reduction in the outer
diameter. These variations in outer diameter are larger
than the design of known connectors of the types discussed
below will accommodate, hence the number of specific sizes
of cable sheath required to fit a complete range of cables
is increased by constraints arising from the design of con-
nectors, whereas it is desirable to reduce the number of
cable sheath sizes to the.limit go~erned by the cable sheath
manufacturing process and by the cable specifications.
One specific type of connector is disclosed in
Canadian Patent No. 651,417 issued on October 30, 1962 to
the same assignee as the present application. The connector
comprises a hollow tubular body adapted to fit over the end
of the sheath and having gripping tongues located on the
inside surface of the tubular body which engage the groove
of the sheath, and a sheath stop. This arrangement permits
the connector to be threaded over the sheath until the
sheath end is binding tight against the sheath stop. One
limitation of this type of connector is that there is a
limited area of contact between the connector and the sheath
with the result that the electrical connection may not be
adequate under some extreme conditions of use. Another
limitation of the above connector is that it is designed to
fit cable sheaths having relatively fixed outer helix dia-
meters and a more limited range of corrugation depth than
is possible.
Another type of connector is disclosed in Cana-
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dian Patent ~o~ 664,108 issued on May 28, 1963 to the same
assignee as the present application. Such a connector is
a more complex type designed to obtain a moisture seal on
a cable with no jacket over the corrugated sheath. ~his
connector is provided with a sheath gripping ring having a
non-circular aperture for binding the sheath against the
sheath stop, instead of the gripping tongues of the above
mentioned Canadian Patent No~ 651,417. The contact area of
such gripping ring is greater than the previously mentioned
gripping tongues, but is still not sufficient to provide
current conduction adequate for some extreme conditions of
use. In addition, this connector is also designed to fit
cable sheaths with relatively fixed outer helix diameters
and an ever more limited range of corrugation depth than
the connector disclosed in Canadian Patent No. 651,417.
Another similar connector is al50 known having a
tubular body with a continuous internal helical groove of
the same pitch as the corrugated sheath in place of the
sheath gripping tongues or ring used in the above~mentioned
patents. This connector provides some contact pressure
between the internal surfaces of the connector and the
sheath when the connector is threaded up to the point where
the internal helical groove runs out. However, it does not
provide for a certain penetration of any aluminum oxide on
the sheath surface, the presence of which is detrimental to
the conduction of induced sheath currents. This connector
is also designed to fit cable sheaths with relatively fixed
outer helix diameters and a more lim,ited range of corruga-
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tion depth than is possible.
A further similar connector is known having aninternal helical ridge which is ~lattened along a plane
substantially parallel to the longitudinal axis of the con-
nector forming sharp edges at the sidewalls of the ridge,
These sharp edges will penetrate any oxide on the surface
of the sheath at any point where sufficient force is gene-
rated between the edge and the surface of the sheath with
which the edge comes into,contact as a result of the action
of threading the connector onto the cable sheath. A major
disadvantage of this connector is that like the connector
described in the preceding paragraph the internal ridge and
the corresponding grooves "runs out" in the manner commonly
known in the art of producing screw-threads. This "run-out"
may cause the respective axes of the connector and sheath
to be at an angle with each other and prevent the sharp
edge from contacting the sheath substantially throughout its
length. ~he degree of this misali~nment may increase as the
outer diameter of the cable sheath decreases when this con-
nector is used for cables having significantly varyingdepths of corrugation and outer diameter.
It is therefore the object o~ the present in~en-
tion to provide a connector for corrugated-metal-sheathed
electric cables which insures an improved electrical connec-
tion between the connector and the sheath and which, in ad-
dition, will allow greater variations in the depth o~ cor-
rugation and the consequent ~ariations in the outer helix
diameter of the cable sheath.
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s
The connector, in accordance with the in~ention,
is of the type comprising a hollow tubular body including a
first portion having a helical ridge provided with a sharp
edge and extending inwardly from the interior surface of the
tubular body of the same pitchas the helical grooveof the
corrugated metal sheathed electriccable for threadingon such
sheath, a secondportion comprisinga gap, orundercut, which
consists of a longitudinalsection cut away toan internal dia-
meter at no pointless than the maximumouter diameter of the
cable sheath intendedto be accommodated withinthe connector,
a third portion adapted to be securedto a standing structure,
and a radially inwardly extending shoulder within the hollow
tubular body betweenthe second and thirdportions and consti-
tuting a sheath stop,whereby the connector maybe secured to
the sheath with the end of the sheath received within the
; first and second portions of the tubular body and in abut-
; ment with the sheath stop. The helical ridge extending
.~ inwardly from the interior surface of the first portion of
the tubular body ends short of the sheath stop so as to
leave the above mentioned gap between the end of the ridge
and the sheath stop to allow the sheath to pass through and
completely abut with the sheath stop, and to align the con-
nector with respect to the cable sheath, thereby causing the
; sharp edge of the helical ridge to cut into the surface of
the sheath substantially throughout its length.
In a second embodiment of the invention, a sealing
grommet and a packing nut having an integral retaining ring
adapted to be threaded into the end of the tubular bo-
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dy are provided for sealing the cable against water and
dust.
The connector is preferably made of aluminum or
aluminum alloy, but may be of any suitable metal.
The invention will now be disclosed, by way of
example, with reference to the accompanying drawings in
which:
:,,
Fiyure l illustrates a perspective view of a dry
type connector in accordance with the invention;
Figure 2 illustrates a section view thro~gh the
connector of Figure l with the sheath and cable removed;
Figure 3 illustrates a perspective view of a wet
type connector in accordance with the invention;
Figure 4 illustrates a section through the connec-
tor of Figure 3 with the sheath and cable removed;
- Figure 5 illustrates a portion of Figures 2 and 4
depicting an alternative typical shape of the groove defi-
ned by the helical ridge of the connector; and
Figure 6 illustrates a portion of Figures 2 and 4
depicting a further alternative typical shape of the groove
: defined by the helical ridge of the connector.
Referring to Figures l and 2, there is shown a
connector of the so called dry type comprising a hollow tu-
. bular body l~ having a first portion 12 adapted to receive
a cable sheath 14, a second portion 16 consisting of an un-
dercut or gap of predetermined length "a" through which the
cable sheath may freely pass and a third portion 18 for at-
tachment to a standing structure. The first portion 12 is
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provided with a helical ridge 20 extending inwardly from
the entire surface of the tubular body having a pitch cor-
responding to the pitch ~ the groo~e 21 on the cable
sheath 14~ The internal ridge 20 of the first portion of
the tubular body includes ~ flattened portion forming sharp
edges 22 with the sidewalls of the ridge. An integral
shoulder 24 is located near the boundary ~etween the second
and third portions of the tubular body for butting the ca-
ble sheath during threading of the connector onto the cable
1 10 sheath. The second portion 16 is cut away to form the gap
"a" between the end of ridge 16 and the sheath stop or
- shoulder 24 so as to pre~ent jamming o the connector befo-
re a~utment with the sheath stop or shoulder 24, or misa-
lignment of the connector with respect to the cable sheath.
The gap, or undercut, "a" will permit easy threading of the
connector onto the cable sheath by hand until the end of
the sheath abuts the shoulder 24. Further effort to tigh-
ten the connector onto the sheath will cause the sharp edge
22 to cut into the side of the crest of the corrugations on
the sheath substantially throughout the helical length of
the ridge 20 and penetration of any oxide layer formed on
such sheath. This is achieved because the un~ercut allows
the connector to centre itself on the sheath. The third
portion has a shoulder 26 and external threads 28 for ins-
tallation `through standard knoc~oùt openings or into stan-
dard threaded openings in terminal boxes or other electri-
cal fittings.
Another important feature of the invention is
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that the outer helix diameter of the cable sheath may vary
significantly for a given size of connector because of the
self-alignment mechanism which allows the sharp edge 22 to
cut into the side of the ridge of the sheath at various
heights throughout the helical length of the ridge 20.
Referring now to Figures 3 and 4, there is shown
a connector of the so-called wet type. The connector com-
prises a hollow tubular body 30 having a first portion 32
provided with a helical ridge 34 identical to ridge 20 of
Figures l and 2, a second portion 35 consisting of a gap,
or undercut, of length "a`', and a third portion 36 for at-
tachment to a standins structure, such as a terminal ~ox.
A sheath stop 38 is located near the boundary between the
second and third portions of the tubular body for the same
purpose as in Figure 2 of the drawings. As shown in Figure
4, the internal ridge 34 also includes a flattened portion
forming sharp edges 40 for the same purpose as sharp edges
22 of Figure 2. The first portion 32 is provided with ex-
ternal threads for screwing an hexagonal nut 42 which com-
presses a sealing grommet 44 onto the cable to provide awater and dust-tight seal. The third portion 36 of the tu-
bular body is provided with an hexagonal shoulder 46 for
permitting tightening of the packing nut and with external
- threads 48 for installation through the standard knockout
openings or into standard threaded openings of terminal
boxes or other electrical fittings~
Referring now to Figures 5 and 6 there are shown
alternative shapes of the groove or trough 50 defined by
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the helical ridge 20 of Figures l and 2 ~or by the helical
ridge 34 of Figures 3 and 4~ The shape illustrated in
Figures 1 to 4 may be termed arcuate. The shape of the
groove 50 s~own in Figure 5 may be termed trapezoidal while
the shape ~f the groove 50 shown in Figure 6 may be termed
rectangular. It is envisaged that still further shapes
which will successfully accommodate the cable sheath may be
employed.
;~ Tests of stability of resistance between an assem-
bled cable sheath and connector, and a metal plate which
served as the simulation of a typical electrical enclosure
panel were conducted. The connectors and sheaths were as-
sembled into simulated three phase installations, a~d sub-
jected to a current cycling test, each cycle consisting of
four hours on and four hours off (three cycles per day) with
the sheaths short-circuited for a total of lO0 cycles. The
results of these tests indicated an initial cold resistance
of 0.043 m ~ and a maximum cold resistance of 0.23 m~ during
the whole test procedure. Similar tests were made on other
known connectors and, in all cases, the connector in accor-
dance~with the invention exhibited a lower resistance and a
higher degree of stability. The current used was that indu-
ced in the sheath by the maximum rated current in the cable.
- The corrugated metal sheaths are usually made of
aluminum or an aluminum alloy and the connectors are also
preferably made of aluminum or aluminum alloys, but both may
be made of any~ suitable metal or combination thereof.
Although the invention has been disclosed with
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re~erence to pre~erred em~odime~ts, it is to be understood
that other alternatives of such embodiments are also envi-
saged~
