Note: Descriptions are shown in the official language in which they were submitted.
~lET~OD OF MARING A CABLE: TBRMINA~OR
BACRGRO~lND OF THB INVE1!JTION:
1. ~iel~ of ~he Invention-
The present invention pertains to electric cable
terminations, and in particular, to terminations for
5 electric cables used for electric power distribution.
2~ De~cription of the Rel~te~ Art.
Electric cables having concentric neutral
conductors and embedded wire conductors are becoming
10 increasingly popular. For example, such cables are used
in direct burial, Underground Residential Distribution
(URD) applications. These cables are typically operated
at thousands o~ volts, and hence, care must be taken in
managing or controlling the electrical stress at points
15 where the cable is terminated for coupling to electrical
components such as switchgear units, for example.
Such cables typically include electrical
shielding surrvunding the central current-carrying
conductor. For example, cables can include a concentric
20semi-conducting jacket, concentric metallic foil
wrapping, or concentrically wrapped, discrete drain
wires. The various arrangements of semi-conducting and
conducting layers surrounding the central
current-carrying conductor control the electric stress
25and induced electrical fields surrounding the central
conductor, features which are important for direct burial
and the like applications.
Cable terminations typically require removal of
the various dielectric, semi-conducting and conductive
30shield layers surrounding the central current-carrying
conductor with the various semi-conducting and conducting
surrounding layers being appropriately connected to the
electrical equipment involved. For example, a porcelain
-2- ~ 3 ~
termination kit is available from the Minnesota Mining
and Nanufacturing Company as SCOTCHCAST 5903. The kit,
which is field-installed, provides termination for
concentric neutral URD cable having a semi-conducting
jacket surrounding the cable insulation, disposed within
a helical wrap of much smaller gauge concentric wires,
commonly referred to as drain wires. The various layers
of the concentric neutral cable are removed in the field
following closely dimensions laid out in the installation
instructions accompanying each kit.
For example, the drain wires are pulled back to
expose a predetermined length of the cable
semi-conductive jacXet. A bottom end cap is inserted
over the semi-conductive jacket and forms a lower seal
therewith~ The semi-conductive jacket is cut back at a
15 predetermined distance from the cable tip, as is the
cable insulation, exposing a predetermined length of the
bared current carrying conductor~ A series of different
tapes are wound about defined sections of the prepared
cable end. Vinyl plastic electrical tape~
20 semi-conducting tape, and stress control tape, for
example, are employed.
A porcelain insulator is disposed about the
prepared cable end and a mounting ring is slid underneath
the porcelain insulator before its insertion in the
25 bo~tom end cap. A top cap includes a recess for
receiving the current-carrying conductor, and includes a
threaded hole ~or receiving a pour spout. An elastomeric
compound commercially available as SCOTCHCAST 2100 is
poured through the top cap to fill the interior o~ the
30 porcelain insulator. The hole i5 plugyed with a threaded
sealing plug. The entire assembly of the termination,
including pouring of the elastomeric compound i
performed in the field and is therefore subject to
different temperature and humidity condition67 ~or
35 example.
3 ;~ ~ 5 ~ 3 . ~ ~
It has been found during development of the
present invention, that the ~irst 20 hours or so of the
curing of an elastomeric compound is p~rticularly
critical to the subsequent performance of that cast
compound in a high voltage electrical insulation system.
As those skilled in the art will recognize, it is
difficult to maintain carefully controlled conditions in
the field, let alone for an extended period of time such
as a 20-hour period ~ubsequent to the casting of th~
elastomeric compound. As described, the cable is
inserted in the porcelain insulator before the
elastomeric compound is poured and thus, the resulting
cured compound structure takes on the diameter of the
cable portions disposed within the porcelain insulator.
Experience has shown that elastomeric fillers applied in
~he field do not offer good performance at low
temperatures and that, due to different coefficients of
thermal expansion, a gap between the filler and the cable
might result.
A terminator commercially available from Joslyn
20 Manufacturing Company, Stock Item #E5200 provides a
porcelain termination with a stress relief cone which is
loaded inside the porcelain insulator at the lower end
thereof, and an elastomer sleeve is inserted between the
prepared cable end and the porcelain insulator bore. In
25 order to eliminate air gaps between the sleeve and
porcelain and the sleeve and cable insulation, a
compression ~pring of considerable strength is loaded
into the top of the porcelain insulator, surrounding the
upper end of the prepared cable end. An upper cap is
30 secured to the porcelain insulator to maintain the spring
in compression. A relatively large number of components
and a higher level of expertise are required for
assembly. Further, neither the stress relief cone nor
the elastomer ~leeve bond to the porcelain insulator and
35 thus, air voids at the interface between these members
. , , .. ,, , .. ~ .. , , .. , . ... ~ ., ~ .. . .... . .
-4~
and the porcelain insulator may ultimately lead to
dielectric failure.
A porcelain termination sold hy the G & W
Electric Company, assignee of the present invention, is
commercially available under the trade designation
"Slip On Terminator." This termination employs a
porcelain insulator which slips o~er a prepared cable
end. A len~th of sponge tubing is inserted between the
prepared cable end and the inner bore of the porcelain
insulator, and also in a mounting base which is disposed
10 below the insulator, also surrounding the prepared cable
end. The sponge does not bond to the inner bore of the
porcelain insulator and greater retention strength at low
temperaturPs is desired.
As mentioned above, it is important to control
15 the electrical stress at the prepared cable end. Of
particular interest is the control of electrical stress
at abrupt changes in the cable shielding system. One
araa of concern is the point whers the semi-conducting
layer is cut away, thus creating a discontinuity in the
20 electrical field surrounding the cable. Heretofore,
measures have been taken to directly bond metallic base
mountings at the bottom end of a cable termination, so as
to position the ground plane at a portion o the cable
termination which is designed to handle the electrical
25 stress. It i5 desirable to provide a ground plane at the
bottom of the cable termination which extends through the
various termination components and which adapts to
thermal changes in cable size, to eliminate interstices
that may form between the various termination components,
30 particularly the cable and a metallic support base. It
may also be desirable in some circumstances to establish
a ground plane without direct contact with the cable
components.
Further improvement~ in metallic support bases
35 are desirable to insure an hermetic sealing between the
... ~, , , .. , , . . . , .. . ~.. , ,.. " .... . .. .. . .
Z~5~
metallic base and the porcelain insulator resting
thereon. To be commercially attractive, such hermetic
sealing should be easy to install and economical to
fabricate. Heretofore, oil-filled terminations have been
provided to address many of the above concerns. For a
5 variety of reasons, which have long been recognized in
the industry, it is desirable to eliminate liquid-~illed
terminations.
SUNNARY OF ~H~ INVEN~ION
It is an object according to the present
invention to provide a method of manufacturing a cable
termination which is economical, which uses a minimum
number of inexpensive parts and which maintains a tight
grip on the cable over a variety of cable operating
15 temperatures and environmental temperatures.
Another object according to the present
invention is to provide a cable termination o~ the
above-described type which is fabricated in a factory
under controlled conditions and which is quickly and
20 easily installed in the field with a minimum amount o~
expertise and without requiring special tools.
A further object of the present invention is to
provide a cable termination having a metallic base member
which forms a ground plane passing through a precisely
25 located medial portion of the ceramic insulator to
provide efficient electrical stress control.
Another object according to the present
invention is to provide an electric termination having a
metallic base member which provides an effective ground
30 plane of the above-described type, but which is
encapsulated within a ~iller which maintains a void-free
engagement with the cable and porcelain insulator despite
temperature changes.
~nother object according to the present
35 invention is to provide a cable termination in which air
~ . . . . ..
-6~
pockets and interstices internal to the porcelain bushing
are avoided, thus precluding ionization, especially in
regions of high electric field.
The~e and other objects of the present .invention
which will become apparent from studying the appended
description and drawings are provided in a method of
fabricating a cable termination, comprising the steps of:
providing a rigid housing having a bore wall
defining an inner bore;
providing a mandrel;
coaxially disposing said mandrel within the
housing bore;
pouring a dielectric polymer betwean the mandrel
and the housing bore wall;
curing the polymer so as to fo~m a substantially
incompressible, but nonetheless deformable, flexible
dielectric liner having a cable-receiving bore; and
removing the mandrel so as to open the
conductor-receiving bore.
BRIEF D~SCRIYTION OF TH~ DR~WING~
In the drawings, wherein like elements are
referenced alike:
FIG. 1 is a fragmentary cross-sectional
elevational view of a portion of a cable termination
assembly illustrating principles according to the present
invention:
FIG. 2 is a perspective view of a termination
assembly with the top cap removed;
FIGS. 3 and 4 are fragmentary cross-sectional
elevational views thereof;
FIG. 5 is an electrical field plot overlaid on a
schematic outline of a fragment of the cross-sectional
view of FIG. 1:
FIG. 6 is an exploded elevational view of a
35 mandrel assembly according to the present invention; and
3~
FI&. 7 is a cross-sectional elevational view of
a housing and mandrel assembly according to the present
invention.
DETAIL~D D~SCRIPTI0~ OF qH~ P~FERR~D ~NEODIN~NTS
Referring now to the drawings, and initially to
FIGS. 1 and 2, a cable termination constructed according
to the assembly method of the present invention is
generally indicated at 10. As will be seen herein, the
cable termination is a "dry" termination, that is, n~t
oil-filled and is fitted on a prepared cable end without
requiring special tools or expertise. Essentially, the
cable termination subassembly is comprised of a porcelain
housing 12 and a dielectric liner or filler 14~ The
filler 14 is cast in the porcelain housing at the
factory, under controlled conditions, and is shipped to
the field, fully assembled, for installation as required.
Referring now to FIG. 1, the completed cable
termination assembly 10 includes a porcelain housing
generally indicated at 12 defining a central bore, a
dielectric liner 14 of substantially incompressible, but
nonetheles~ deformable, resilient or flexible material,
and a metallic support base generally indicated at 16.
The housing 12 is preferably o~ conventional porcelain
construction, comprising a generally tubular wall 20, and
25 a series of skirts 22, outwardly extending from the wall.
The inner surface 24 of wall 20 as shown is cylindrical,
but can have other shapes, if desired. Wall ~0 include~
upper and lower generally annular end members 30, 32.
FIG. 1 shows a completed terminator assembly
30 with a high voltage electrical cable generally indi~ated
at 36, installed therein. Cable 36 may be of the
concentric neutral or embedded wire type, for example, as
is commonly used in electrical distribution systems for
Underground Residential Distribution (U~) applications.
35 In the preferred embodiment illustrated in the figures,
-8- ~ 5~ ~
cable 36 has a semiconductor layer 40 disposed around an
insulating layer 41 covering a cen~ral metallic conductor
42. The cable 36 further includes an outer diele~tric
jacket 44.
As can be seen in FIG. 1, the multi-layer cable
36 has been prepared for assembly with the cable
termination 10. For example, the outer dielectric jacket
44 has an upper free end 46 disposed n~ar the bottom of
the termination, and the semi-conductive layer 40 has an
upper free end 48 forming a step with respect to
insulating layer 41. The conductor 42 and insulating
layer 41 together comprise a conductor means or cable
inner layer which is inserted in the termination, as will
be seen herein. As those skilled in the art will
appreciate, termination 10 allows the central
15 current-carrying conductor 42 to be bared at 43, and to
extend beyond the electrical shielding system of the
cable, which otherwise controls the electrical stress and
electrical fields present when the conductor is
energized.
According to an important aspect of the present
invention, hou ing 20 is filled with an elastomer
material which is cast in plase, within housing 20, prior
to insertion of cable 36. ~he generally tubular liner 14
is produced by this casting. The elastomer material of
25 liner 14, when cured, preferably comprises a
substantially incompressibl~ but nonetheless deformable,
resilient material which maintains the shape over the
operating range of cable temperatures, so as to follow
motion of the cable sur~ace as the cable expands and
30 contracts. The following are examples of suitable
elastomer materials: low durometer polyurethane, low
durometer silicones and flexibilized epoxies. The
preferred material is a low durometer polyurethane
commercially available as a potting and encapsulating
35 compound under the trade designation of CASTALL UX~7544,
-9~ ~,",,~j
availa~le from CASTALL, Inc., of East Weymouth,
Massachusetts. Those skilled in the art will be abl~ to
readily determine other suitable elastomer materials,
based upon teachings of the present invention.
As one feature of the present invention, the
elastomer materi~l, when cast within ho-~sing wall 20,
forms a bonding with the inner wall surface 24.
Preferably, the bonding is substantially continuous
throughout the interface between the liner 14 and the
wall surace 24 so as to prevent pockets or other
interstices which might break down electrically under the
high electric fields set up by the current-carrying
conductor 42~ At a minimum, the bonding eliminates large
size voids, large numbers of linearly aligned smaller
size voids, and large numbers of closely spaced smaller
size voids. Such would, of course, degrade the
insulation value of the termination and if breakdown were
to occur, might significantly shorten the useful life of
the termination assembly.
As mentioned above, electrical terminations have
20 been proposed and are in use today, which have
elastomeric compounds poured into the space between a
porcelain insulator and an electrical cable previously
inserted therein. Such elastomeric compounds are poured
in the field, under field conditions. In contrast, the
25 liner 14 according to the present invention, is cast
within insulator housing 20 prior to insertion of an
electrical cable therein. The liner 14 is cast to ~orm
an inner bore, when cured, has a neck portion of size
slightly less than the size of the current-carrying
30 cable, a feature not possible with elastomers cast in the
field to surround a cable previously inserted in an
insulator housing.
With the precast liner of the present invention,
a certain amount of insertion force must be exerted on
35 the cable inner layer to install the cable in the
-10- 2~ J~3.
termination assembly. However, the liner material is
flexible and deformable without sacrificing substantial
incompressibility, shape retention and resilience, and
thus, an intimate void-free engagement of the liner
throughout the length of the conductor is assured and
minor irregularities in the outer surface of insulating
layer 41 may be accommodated by liner 1~, assuring an
intimate engagement which is not compromised over the
useful life of the termination assembly. Such engagement
is important to prevent electrical breakdown and also to
prevent intrusion of contamination within the termination
assembly.
Provision is made when casting liner 14 to
accommodate the increased size of the upper end of
semi-conductive layer 40. Referring to FIG. 3, a pocket
49 is formed with an upper wall 51. The pocket 49 is
generally cylindrical to reduce push-out of the cable.
The pocket 49 forms an enlarged end of the
cable-receiving bore to aid in cable insertion. In the
preferred embodiment, a plurality of annular ribs 53
20 provide an elastomeric seal with the cable, and in
particular, the semiconductor layer 40 thereof. The ribs
53 are formed such that their root portions are of
~enerally the same size as the semiconductor layer~ with
the protruding portions of the ribs being flattened when
25 the cable is inserted. A dielectric grease may be
employed when insexting the cable to displace any trapped
air in pocket 49. The cable is inserted until the free
end of the semiconductor layer engages wall 51.
As can be seen in FIG. 3, a generally
30 cylindrical neck portion 55 is located above pocket 49.
The neck portion 55 is undersized relative to the cable
insulating layer 410 An upwardly expanding tapered
portion 59 is located above neck portion 55. The tapered
portion has an upper free end 61, which is recessed ~elow
35 the upper surface of housing wall 20. A protective cap
,q~,t~
63 (see FIG. 1), preferably of stainless steel, prevents
water and air borne contaminants from settling in this
recessed area, the upper cap being particularly desirable
when the termination assembly is installed outdoors. A
compression terminal 45 is crimped onto conductor 42
after the tip of the conductor is pushed through cap 63.
A conductive rubber sealing boot 67 covers the upper end
of the a~sembly and a non-conductive rubber sealing boot
65 covers the lower end, as will be seen herein.
According to another aspect of the present
invention, a base support generally indicated at 16 is
provided to support the cable and the termination 10.
The base 16 includes a lower, generally horizontal plate
member 52 having an aperture 54 for receiving a screw
fastener to provide a convenient mounting for the
termination to a supporting structure. The base 16
includes an annular portion 56 underlying the insulator
housing so as to engage the lower enlarged annular end 32
thereof. Annular portion S6 is preferably merged with
plate 52. As those skilled in the art will appreciate,
the joint 57 between the bottom end of the insulator
housing and the base 16 may experience intrusion of
moisture and contaminants which might migrate inwardly
toward the center of the termination assembly, over a
prolonged period of time.
Accordingly, it is desirable to eliminate such
intrusion at the ioint between the housing and base and
according to one aspect of the present invention, an
upstanding annular collar 60 is provided to surround the
joint between the housing and base member. The collar 60
has an upper surface 62 extending above the bottom of the
insulator housing, preferably extending to the top of the
enlarged annular end 32 of the housing. Collar 60 forms
a recess into which a sealant 66 is cast. The sealant
may be of any suitable material, but preferably bonds to
35 the base 16 and the housing 12, so as to provide an
-12~
hermetic seal. Preferably, the sealant will maintain the
bond with the insulator housing and base, despite
temperature variations causing expansion and contraction
associated with the thermal coefficients of expansion of
economical housing and ~ase materials.
According to another aspect of the present
invention, the base 16 includes an optional upstanding
shield 70 extending part way into housing 20. The shield
70 is preferably provid~d as an integral portion of base
16, which as mentioned, is made of a conductive,
preferably metallic material. The base 16 is
electrically grounded, and thus, the upstanding shield 70
i5 at ground potential. The shield 70 extends above the
upper end 48 of semi~conductive layer 40 sufficiently to
minimize the electrical stresses at upper end 48. In the
preferred embodiment, the upper end 72 of shield 70 is
located adjacent an enlarged thickness portion of housing
20, herein the lowermost skirt 22a. As can be seen in
the electric field plot of FIG. 5, the electric field
lines 76 emanating from the free end of the
20 semi-conductive layer are concentrated at the increased
thickness portion of housing 20, which is better able to
withstand the electrical stress than thinner portions of
the housing. The shield ~ree end 72 can be located
elsewhere, if desired, away from a skirt member. Thus,
25 the relatively expensive porcelain material can be
reduced in thickness with the optional upstanding shield
according to the present invention. Also, quite
importantly, as can be seen in FIG. 5, the joint between
the insulator housing and base is effectively shielded
30 from electrical stress.
If desired, the upstanding shield 70 can be
installed after liner 14 is cured. However, the factory
casting of liner 14 made possible with the present
invention provides significant advantages if an
35 electrical shield member or a simpler base without an
-13~
electric shield member is desired for the termination
assembly. In the preferred embodiment, the base member
16 is installed prior to casting o~ liner 14, the liner
material flowing to surround the shield 70, and to
provide an intimate void-free seal between the shield,
housing and cable, and optionally the annular support
portion of base 16.
Contrary to a commonly held belief in this art,
the electric shield 70 has been found to function very
well as an electric shield, even though it is separated
from semi-conductive layer 40 by a thickness o~
dielectric liner 14. Of course, the semi-conductive
shield 40 must be bonded to a circuit element which is at
ground potential, according to currently accepted
practices in the industry. Thus, the semi-conductive
layer ~O and shield 70 are both at ground potential and
the innermost electric field line 76a plotted in FIG. 5,
represents a line of approximately zero potential, i.e.,
the receding ground plane, when conductor 42 is
energized.
As mentioned above, the neck portion 55 is
undersized relative to the cable insulating layer 41.
The cable end is prepared as explained above, with
various outer layers removed at appropriate points along
the cable length. For example, the semiconductor layer
25 40 is cut back from the cable free end at a distance
which ensures the cut end 48 engages wall 51 of pocket 49
(see FIG. 3), thus provi.ding a convenient tactile
indication that desired orientation relative to shield 70
has been achieved. The inner layer of the cable,
30 comprising the conductor 42 and sur.rounding insulating
layer 41, is inserted in the lower, enlarged end of the
liner bore and is pushed through the neck portion 55,
displacing liner material 14a from the neck into the
tapered portion 59 as indicated by arrow 71 of FIG. 4.
35 The liner material is incompressible and flexible and
-14~ 3.~
exhibits sufficient compression set resistanc~, so as to
retain its cured shape despite deformation, and hence the
cable is securely gripped by liner 14 despite changes in
temperature and variations in conductor size. Thus, an
interference fit can be Pnsured under all expec~ed cable
operating conditions. The liner is ~oft, but still tear
resistant and easily follows motion of the sable surface
maintaining a "dry" void-free engagement therewith, as
the cable expands and contracts with temperature changes.
Turning now to FIGS. 6-7, a method of
fabricating the termination assembly will now be
described in greater detail. ~s mentioned above, the
liner is cast before insertion of the cable in the
termination assembly, the liner having a central bore
slightly smaller in size than the cable insulation layer.
FIGS. 6-7 illustrate a further refinement to the casting
of the liner so as to provide certain advantages as will
be described herein. FIG. 6 shows a mandrel assembly
generally indicated at 86. The mandrel assembly includes
a post member 88, an end member 90 and a bolt fastener
92. According to one aspect of the present invention,
the post member 88 has a tapered, part conical portion
96. The conical portion 96 of post 88 is disposed
between generally cylindrical end portions 98, 100
disposed at the outer free end and inner end of the post
25 member, respectively. End portion 100 defines a threaded
bore 102 for receiving bolt 92. End member 90 has a
generally cylindrical configuration with a series of
annular indentations 104 formed therein, and includes a
central bore through which bolt 92 is inserted. The
30 annular indentations 104 form the series of ribs 53 which
function like 0 rings, providing an elastomeric sealing
o~ the semiconductor portions of the cable.
Referring no~ to FIG. 7, the mandrel assembly 8
is disposed along the central axis 103 of housing 12.
35 Preferably, end member 90 is seated within a tapered bore
~15- 2~
portion 108 o~ base 16. An 0-ring gasket 105 is located
at the bottom of end member 90. An elastomsr material
such as that described above is poured into the inner
bore of housing 12, filling the space between the mandrel
assembly, the housing wall and the shield portion of base
16. It has been found that approximately the fixst 20
hours of curing of the elastomer is critical to the
proper functioning of the resulting solid liner.
According to one aspect of the present invention, the
elastomer is preferably cured in one stage, but may also
be cured in two stages. If a two-stage cure is employed,
the first stage will provide a room temperature cure for
at least several hours. The entire termination assembly
(with the mandrel assembly installed) is then placed in
an oven, and the second stage of curing is completed, the
temperature in the oven preferably comprising a
temperature at least as great as the maximum temperature
of the termination assembly to be expected during its
operation, usually determined by the maximum overload
condition of the current-carryin~ conductor~
The elevated temperature cure is carried out for
several additional hours with the mandrel optionally
remaining in position throughout the entire curing
operation. Thereafterl the termination assembly is
removed from the oven and allowed to cooled~ The mandrel
is then disassembled by removing bolt fastener 92, and
separating the mandrel post member and mandrel end
members in the directions indicated by arrows 112, 114,
respectively. With installation of top cap 63, the cable
termination assembly is then ready for shipment to the
field, where the prepared electrical cable is inserted
through the central bore of the liner, herein indicated
by the reference num~ral 120.
-16- ~r~ 3~
When a single stage cure is preferred, the terminator
assembly is immediately placed in an oven after assembly,
and is cured at a temperature which is at least as high,
and preferably higher than the highest expected operating
temperature of the cable and terminator assembly.
Several important features of the liner 120 will
now be described. As mentioned above, it is desirable to
have the central bore of the dielectric liner dimensioned
smaller than at least the insulating layer 41 portion of
the electric cable 36~ For the liner fabricated
according to the method of the present invention, a
reduced bore size occurs at the neck portion formed
around portion lO0 of post member g6. As mentioned, the
portion 100 is preferably cylindrical and as can now be
seen is dimensioned to have a diameter substantially less
15 than the diameter of insulating layer 41.
In order to aid the insertion of the insulating
layer through the liner 14, the end member 90 is provided
with an enlarged diameter, so as to create an enlarged
opening or pocket at the lower end of the liner.
20 According to one aspect of the present invention, the
enlarged opening is preferably provided with one or more
ribs 53 which function as 0-ring structures to provide a
sealing with the semi-conducting layer 40, although the
rib structures 53 can be omitted if desired. The pocket
25 may be tapered if desired, but it has been found that
significant push-out forces result, which tend to expel
the prepared cable end from liner 14. Accordingly, it is
preferred that the pocket be made generally cylindrical
with a significant step wall 51 which provides a
30 pronounced stop for abutting engagement with the cut free
end of semiconductor layer 40, so as to provide a tactile
indication that the semiconductor end is spaced a
preferred distance from the tip 72 of shield 70, which
positioning cannot be readily visually determined. Due
3.~
-17-
to the soft, deformable nature of the liner, as the
inner cable layer is inserted in the inner liner bore,
liner material is displaced in the direction of cable
insertion, indicated by the arrow 124 of FIG. 3.
According to one aspect of the present
S invention, the tapered portion 96 of post member 88 has
cross-sectional sizes larger than that of the insulation
layer, and thus, forms a cavity at a downstream portion
of the undersized liner segment. This cavity allows
liner material to "flow" or be displaced in the direction
of cable insertion, without generating forces within the
housing or tearing the liner. As a result, an intimate
engagement between the liner and inner cable layer can
easily be achieved throu~hout the axial length of the
liner and such has been readily verified during the
course of developing the present invention~ If desired,
however, the kapered portion 96 can be reduced or
eliminated i~ the bore of the liner is undersized only a
slight amount, although it is generally preferred to
provide the tapered portion as described above.
The liner material, despite being deformabl~ and
flexible, is sufficiently tough, so a~ to resist tearing,
especially at the displaced portions. Further, the
material is substantially incompressible, exhibiting
compression set resistance, particularly in the neck
25 portion even when subjected to elevated temperatures for
prolonged periods of time, as might be expected in most
service conditions. Pulling grease is optionally used to
reduce the possibility of tearing the liner. A
dielectric grease may be used to purge pocket 49 of air.
The drawings and the foregoing descriptions are
not intended to represent the only forms of the invention
in regard to the details of its construction and manner
of operation. Changes in form and in the proportion of
parts, as well as the substitution of equivalents, are
35 contemplated as circumstances may suggest or rend~r
~ ~t~
-18-
expedient; and although specific terms have been
employed, they are intended in a generic and descriptive
sense only and not for the purposes of limitation, the
scope of the invention being delineated by the following
Claims.
