Note: Descriptions are shown in the official language in which they were submitted.
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MVSSPECl9/11886a
FIELD OF THE IN~NTION
This invention relates to electrical cable
glands and, more particularly, to electrical cable
glands embodying moisture-proof seal arrangements
designed to prevent the ingress of moisture and dirt
into the interior of the cable gland with the
objective of minimizing or obviating corrosion of
metallic conductors or parts in the interior of the
cable gland.
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Still more particularly, but not exclusively,
the invention is directed towards electrical cable
glands which embody an armor clamp assembly for
mechanically clamping the ends of armor wires within
the cable glands and in wnich case, the seal
arrangement is intended, in amongst other things, to
protect the armor wires against corrosion in use.
BACKGRO~ND TO THE INVENTION
There are numerous different designs of
electrical cable glands on the market and which
embody inner and outer seals, the outer seal being
adapted to seal onto the outer sheath of an
electrical cable, in use, and the inner seal being
adapted to seal onto the inner sheath. An armor
clamp assembly is provided between the two seals to
clamp the armor wires of an armored electrical cable.
Such cable gland assemblies can have a weak
point in their design in that, in most cases, an
internally screw-threaded tubular member receives an
~0 externally screw-threaded member and moisture or
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vapors can travel along the screw-thread and thereby
gain access to the interior of the electrical gland
between the inner and outer seals thereof.
One solution proposecl the provision of a
cylindrical sealing surface on the outside of one of
such parts of a cable gland which was to be in
sealing engagement with a peripheral skirt extending
from the other of such parts to bridge the entrance
to such screw-thread.
However, manufacturing tolerances on such an
arrangement have proved to be difficult to maintain
and, whilst such an arrangement operates effectively,
it is the object of this invention to provide a
simplified and more easily manufactured cable gland
which provides an equivalent seal arrangement.
Furthermore, commercially available cable
glands are not particularly well suited to use in
corrosive surroundings such as in submersible pumps
or other submerged locations in corrosive liquids or
~0 simply in corrosive environments such as coastal
locations or chemical plants. The only way in
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which contact with such corrosive li.quids or
environments is prevented is by a rubber or plastics
shroud which generally has not proved to be
satisfactorily effective. It is thus another object
of this invention to provide a cable gland which has
superior corrosion resistance when compared at least
to most prior art cable glands.
SUMMARY OF THE~INVENTION
In accordance with this invention there is
provided an electrical cable gland comprising at
least two tubular parts, a first one of which has an
externally screw-threaded zone co-operating with an
internally screw-threaded zone of the other or second
part, said first part having, in addition, at a
location remote from the internally screw-threaded
second part, a smooth outer sealing surface with
which co-operates an end region of an elastomeric
sealing sleeve, the opposite end region of which is
supported or preformed so as to flare outwardly upon
axial compression thereof, the wall thickness of the
sealing sleeve being small relative to its length so
as to promote flaring and not simply axial
compression, the arrangement being such that,
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upon operative installation, the adjacent end ~ace of
the internally screw threaded second part contacts
and seals against said opposite end region of the
elastomeric sealing sleeve whilst urging the adjacent
end region of the sleeve radially outwardly as the
two parts are moved together by means of the
screw-thread to effectively seal the screw-threads of
the two parts from the exterior.
Further features of the invention provide for
the externally screw-threaded first part to have an
outer skirt spaced radially therefrom but rotatable
in unison therewith, such skirt together with the
said end face of the internally screw-threaded second
part, forming a housing for the elastomeric sealing
sleeve and, against the inner surface of which the
end of the elastomeric sealing sleeve can sealingly
engage in the event it moves sufficiently radially
outwardly; for the elastomeric seal to have a
thickened zone in the region thereof co-operating
with the end face of the second part; for the
electrical cable gland to be of the type embodying an
armor clamp assembly for co-operating with armor
wires on an armored electrical cable, in which case
the electrical gland embodies both an inner and an
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outer seal for engaging the inner and outer sheaths
of an electrical cable in use; and for both the
inner and outer seals to be elastomeric compression
seals.
Still further features of the invention
provide for the second part (having the internally
screw-threaded zone) to have an internal electrically
conductive sleeve having electrically insulating
and/or corrosion resistant material molded onto the
outer surface thereof, for the first part (having
the externally screw-threded zone) also to be made of
electrically conductive metal but to carry an
external electrically insulating and/or corrosion
resistant cover or skirt defining member for covering
exposed metallic parts thereof; and for the entire
surface of the cable gland, in the operative
position, to be formed from such electrically
insulating and/or corrosion resistant material.
Most particularly, such electrically
insulating material is chosen for its corrosion
resistant properties and, accordingly, the electrical
insulation properties may be of secondary importance
and may be absent entirely although corrosion
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resistance is almost invariably associated with
electrically insulating materials.
A still further feature of the invention
provides for an armor clamp to be embodied within the
cable gland and wherein the surfaces of the armor
clamp adapted to engage armor wires, in use, are made
of a material chosen for its resistance to galvanic
corrosion and, in particular, in the case where the
armor wires are of aluminum, for the co-operating
surfaces of the armor clamp arrangement to be made of
stainless steel.
It is preferred that such an armor clamp
arrangement be of the type wherein a truncated
conical clamping member and co-operating conical seat
are employed to clamp the armoring therebetween and
both the seat and the cone member are manufactured as
separate parts and are each held captive relative to
one of the two parts of the cable gland. In such a
case only these two small parts need be made of
stainless steel, or other costly metal chosen for its
resistance to galvanic corrosion when in contact with
the metal from which the armor wires are made and the
other electrically conductive parts of the cable
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gland can be made of brass, optionally suitably
plated, in the normal way. Conveniently the two
parts of the cable gland for the basis for two
sub-assemblies which between them include all
components of the cable gland.
In order that the above and other features of
the invention may be more fully understood, one
embodiment thereof will now be described with
reference to the accompanying drawings.
BRIEF_~ESCRIPTION OF THE DRAWINGS
In the drawings :
FIG. l illustrates, in partly sectioned
longitudinal elevation, a cable
gland according to this invention in
the inoperative position;
FIG. 2 illustrates, in similar view, the
same cable gland in the operative
position installed on an armored
electrical cable, and,
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FIG. 3 is a sectional elevation of a molded
elastomeric sleeve.
DETAILED DESCRIPTION WITH REFERENCE TO T~E DRAWINGS
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In the embodiment of the invention
illustrated in the accompanying drawings, the
electrical cable gland is composed basically of two
sub-assemblies which are co-axial in use and are
interconnected by co-operating internal and external
screw-threads. The cable gland is of the general
type embodying an armor clamp assembly designed to
provide electrical continuity between the armor wires
of a cable and an electrical connection box or an
earth located therein. The cable gland of this
embodiment of the invention is, in addition, designed
to be substantially corrosion resistant and, in
consequence, suitable for use in corrosive
atmospheres and even suitable for use in electrical
connections made in submerged locations such as
submersible pumps or the like.
The one sub-assembly; generally indicated by
numeral l is, in use, adapted to secure the cable
gland to an electrical connection box 2 through an
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an aperture in the wall thereof. In this case, the
electrical connection box is of an electrically
insulating and corrosion resistant material and has
an electrical earth continuity connection 3 located
within the box.
This first sub-assembly has an electrically
conductive externally screw-threaded tubular spigot 4
extending through the hole in the operative condition
and secured therein by means of a suitable conductive
nut 5 or the like to the electrical continuity ring.
Integral with the externally screw-threaded
spigot is an enlarged diameter section 6 whereof the
portion immediately adjacent to the spigot has a
smooth cylindrical outer surface 7 which adjoins an
externally screw-threaded zone 8 whereof the
screw-threads stand proud of the smooth outer surface.
The bore through this first part of the cable
gland also has a step change in diameter with the
larger diameter being remote from the electrical
connection box and housing an elastomeric compression
inner seal 9 adapted to bear against the shoulder lO
formed by the step in the inner diameter.
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The opposite end of the compression seal is
in co-operating relationship with the inner end of a
tubular extension 11 of a cone member 12 having at
its opposite end an armor spreading cone 13 of an
armor clamp of substantially conventional design.
The cone member is held captive relative to the first
part of the cable gland by an outwardly flared inner
end of the extension (indicated by numeral 14) and a
co-operating inwardly directed peened lip 15 at the
end of the first part remote from the electrical
connection box.
The cone member is thus free to rotate and
move axially relative to the first part of the cable
gland to a predetermined extent.
The first part can be machined from metal in
the usual way but can be substantially thin-walled in
view of the fact that it is ultimately protected from
corrosive attack in the manner described below.
Screwed on to the spigot is a molded
electrically ins~lating and corrosion resistant skirt
defining member 16 having a complementarily
internally screw-threaded hole for receiving the
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spigot and, conveniently, the skirt defining member
is fixed in permanent association with the spigot
simply by means of a suitable adhesive, for example,
a cyanoacrylate type of adhesive.
~n end face 17 of this skirt defining member
is directed towards the wall of the electrical
connection box and is sealed thereto, in use, by a
corrosion resistant electrically insulating washer 18.
The skirt defining member provides a skirt l9
extending over substantially the entire length of the
enlarged diameter section 6 of the first part but
radially spaced apart therefrom to define a cavity
20. This skirt has a smooth cylindrical inner
surface and an hexagonal-shaped outer surface for
: 15 engagement by a spanner whereby the first part can be
rotated during installation.
Clearly, during rotation of the first part by
means of a spanner applied to the skirt definlng
member simply tends to move along the screw-thread of
the spigot portion until it abuts the step change in
diameter whereupon the rotational force is simply
applied to the first part through the step.
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The first sub-assembly is completed by an
elastomeric sealing sleeve 21 which sealingly engages
the smooth outer surface of the enlarged portion of
the first part and is sufficiently long to project
over onto the raised screw-threads thereon, as
illustrated clearly in Fig. 1. It is preferred that
the outermost end of this elastomeric sealing sleeve
be provided with a thickened zone 22 to ensure
proper engagement with the end face of the second
part as described below. Preferably, but not
essentially, the sleeve is molded to a preset shape
such that the end region remote from the smooth outer
surface is flared outwardly as shown in Fig. 3.
The second sub-assembly consists of a tubular
electrically conductive inner part 23 which receives,
in captive manner, a ring 24 also of electrically
conductive material and defining an inner tapered
surface 25 for co-operating with the cone and which
completes the armor clamp assembly. The ring 24 is
2G held captive within this second part by a split-ring
26. ~he other end of this electrically conductive
part is internally screw-threaded to co-operate with
the screw-threads on the enlarged section 6 of the
first part as shown clearly in the drawings.
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Molded onto the outside of the electrically
conductive second part is a covering of electrically
insulating corrosion resistant material 27 which
provides an hexagonal-shaped zone 23 for co-operation
with a spanner.
The molded covering 27 extends over the
entire outer surface of the electrically conductive
second part and, indeed, over the end edge of such
part adjacent the first sub-assembly. The end edge
of the molded material thus provides a sealing face
29 directed towards the elastomeric sealing sleeve 21.
At the other end of the second part the
molded material is formed into a tubular extension 31
having an externally screw-threaded free end 32 with
which co-operates a union nut 33 made of electrically
insulating corrosion resistant material and fo~ming
part of an elastomeric compression seal 34 adapted to
define an outer seal and to co-operate with, and seal
onto, the outer sheath of an electrical cable 35 in
use,
It will be seen that the entire outer surface
of the electrical cable gland is de~ined from
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electrically insulating, corrosion resistant material
which, in the installed condition of the cable gland
protects, together with the sealing sleeve, the
entire metallic internal components of the cable
gland. The only possible place where any metal
could be attacked, is at the junction between the two
sub-assemblies and, in fact, ~ia the screw-threads on
the two co-operating parts of the cable gland and the
seal provided by this invention obviates such contact.
Thus the corrosive materials are kept out of
contact with the metallic components in consequence
of the elastomeric sleeve being urged, in the first
place, longitudinally so that its rear end engages
the inner shoulder of the skirt defining member and,
as the two sub-assemblies are screwed together, the
elastomeric sleeve is contacted firstly with the end
face of the cover material on the second part of the
cable gland. Subsequent rotation of the two
sub assemblies relative to each other causes the end
of the sealing sleeve engaged by the second part to
move radially outwardly and~ ultimately, to tend to
roll back on itself, but, in any event, to seal
against the inner surface of the skirt. In this
manner a complete and effective seal of the joint
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between the sub-assemblies is achieved.
It has been found in practice that an
electrical cable gland made as described above
provides complete protection against corrosion of the
me.allic inner parts which, as will be understood,
provides the required electrical continuity between
the armor wires of an armored electrical cable and
the electrical continuity ring on the inside of the
electrical connection box. In fact, electrical
cable glands of this nature have been employed, at
least for test purposes, in connecting submersible
pumps used for pumping corrosive liquids without any
ill effects to the electrically conductive components
of the cable gland.
The embodiment of the invention descrlbed
above is also adaptable to an application in which,
as opposed to the conventional steel armor wires,
there are employed aluminum armor wires.
Generally speaking, where brass is the
material of manufacture of the electrically
conductive components of an electrical cable gland,
such brass components cannot be contacted directly
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with the aluminum as galvanic corrosion sets in under
those conditions.
In the above described embodiment of the
invention all that needs to be replaced with suitable
conductive metal are the parts actually contacting
the armor wires, namely the armor spreading cone and
the ring defining the co-operating seat therefor.
Only these two components could be made of, for
example, stainless steel and the two electrically
conductive main parts of the cable gland could be
manufactured of brass in the usual way. It is to be
noted that neither the contact between stainless
steel and brass nor the contact between the stainless
steel and aluminum gives rise to galvanic corrosion.
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 it is possible to
apply the lnvention to a two-part cable gland which
does not necessarily embody an armor clamp but which
does have two parts which interengage by means of a
screw-threaded connection in an analogous manner to
that described above.
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