Note: Descriptions are shown in the official language in which they were submitted.
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This invention relates to telecommunications cables and is
essentially concerned with encapsulation of splices formed between wires of a
cable and a branch cable.
A telephone distribu-tion system -From a central off~ce to
subscribers has the yeneral Porm of a tree nekwork in that khere is a ma~n
telecommunications cahle which divides into a plural-ity oF main branch cables
which further subdivide into branches and khence into sub-branches, This
process may continue for many further sub-divisions. The main cable is a
number of multi-thousand pair of cables that run out of the central office.
The cables branch off numerous times before the final branch cable, i.e. the
customer drip wire, branches off. Each of the branching points or nodes
necessitates splicing one cable to another, a pair at a time.
In one current method of splicing cables, the cables are opened
and when the wires are spliced in place they are wrapped with many layers of
sealing tape and closed in with a preformed heat shrinkable split sleeve. An
external heat source has to be applied to the sleeve to raise the temperature
within the sleeve to melt the tapes with the intention of shrinking ~hem onto
the spliced joint and exiting wires. There are at least two disadvantages in
this process. Firstly, because of the sleeve thickness, it takes an
unacceptable amount of time to melt ~he tapes; in some cases this is at least 7
or 8 minutes during heating and 30-50 minutes for cooling. SeGondly, the tapes
only shrink down sufflciently to shape themselves to the splice and cable ends
at the splice. In many cases an open flame from a torch is used to provide the
required heat making the system highly craft sensitiveO
In another method, a cable opening is taped and a split sleeve is
placed around the cable. The sleeve ends are sealed with layers of sealing
tape. The sleeve ends are sealed with layers of sealing tape. The sleeve is
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then flooded with a pouring type encapsulating sealant, such as
polyurethane.
The present invention provides a telecommunications
cable having a splice which is reliably watertight~ The ;nvention
also provides a method of makiny such a cable splice while using
high temperatures during encapsulation and in which no damage is
caused to insulated conductors because of high temperatures.
Accordingly~ the present invention provides a method
of forming a spli:ce in a telecommunications cable between a pair of
bared conductor ends of a first cable and a pair of bared conductor
ends of a second cable comprising:-
drawing a selected pair of conductors from the First
cable through a slit in the cable, providing said conductors with
bared ends, and forming electrical connections between said bared
ends of the first cable and the bared ends of the second cable;
covering the slit, the connections and bared conductor
ends by:-
a) wrapping overlapping and contacting windings of heat
softenable sealing tape around the first cable and beneath the
connections and the bared conductor ends; and
b) wrapping o~erlapping and contacting windings of the sealing
tape in contact with the first windings and around said first cable
and over the connections and bared conductor ends so as completely to
enclose the connections and bared conductor ends in the overlapped
windings;
injection moulding an encapsulation of molten plastic
material around the sealing tape wrapping and around adjacent insulation
covered cable, the injection temperature being sufficiently high to
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soften the sealing tape and merge it into a single mass to cause
the mass to completely and sealingly enclose the bared conductor
ends and connections, the plastic material being compatible with
the material of the insulation to provide a Fluid-tight boncl upon
cooling; and
cooling the encapsulation during which it shrinks upon
the softened sealing tape the resultant pressure causing the merged
single mass of tape to become shaped intimately into fluid-tight
sealing contact with the connection and bared conductor ends.
In the above method, the tape should have heat
insulating properties to limit heat transfer from the injection
moulded plastics to prevent softening and flow of the insulation
covering conductors in cable and beneath the tape. Such softening
and flow could otherwise cause undesirable movement of insulated
conductors towards each other such as to adversely affect the
electrical properties of the cable~ One sealing tape found particularly
useful in this respect is made from an ethylene-propylene rubber.
The invention is of particular interest when the insulation
of the cable is polyethylene. Plastics materials compatible with this
and useful for the injection moulded encapsulation include ethylene
acrylic acid, ionized metacrylic acid and polyethylene.
In the inventive process, it is preferable to use a metal
mould for the encapsulation and ideally this should be water cooled
and/or be a highly heat conductive aluminum. When the encapsulation is
injection moulded, heat transfer from the hot plastics into the mould
forms a cooled skin on the encapsulation to prevent the inclusion and
entrapment of air beneath the skin upon cooling and shrinking of the
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remainder of the encapsulation.
The invention also includes a telecommunications cable
having a splice comprising:-
electrical connections between a pair of bared conductorends of a first cable and a pair of bared conductor ends of a second
cable;
a layer of sealing material sealing by enclosing and
in intimate contact with the connections, bared conductor ends, and
adjacent insulation on cable parts, the layer formed from overlapped
windings of heat softenable sealing tape around the first cable,
beneath and then over the bared conductor ends, the tape heat softened
and shaped into said intimate contact; and
an injection moulded encapsulation of plastics material
completely surrounding the wrapping and adjacent insulation covered
cable, the encapsulation being sealingly bonded to said adjacent
insulation.
In preferred constructions in which outer covering
insulation on the cable is polyethylene, the encapsulation is an
injection moulded ethylene acrylic acid, ionized resins, a polyethylene,
or ethylene vinyl acetate. Examples of these materials which are found
to be compatible with polyethylene insulation are ethylene acrylic acid
sold by Dow Chemical of Canada Limited under their product numbers 459,
455 and 435, ionized resins sold by DuPont under their trade names
'Surlyn 1652' and 'Surlyn 1702', and ethylene vinyl acetate sold by
DuPont of Canada Limited under their product number 3180.
The bond between ethylene acrylic acld and polyethylene
depends upon the amount of acrylic acid in the encapsulation material.
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Grade numbers 459 and 455 have an acrylic acid content of around 8%
by weight of the ethylene acrylic acid and achieves a better bond
than grade 435 which has an acrylic acid content of about 3.5%.
Also, in preferred constructions, the layer oF sealing
material is surrounded by a layer of material wh;ch remains l~nsoftened
at the heat softening temperature of the sealing rnaterial, or,
effectively, in the performance of the process, at the injection
moulding temperature.
Embodiments of the invention will now be described, by
way of example, with reference to the accompanying drawings in which:-
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Figure 1 is an isometric view of a splice of four drop wires from
a main telecommunications cable;
Figure 2 is a cross-sectional view along the axis of the splice
in Figure l;
Figure 3 is a cross-sectional view across the axis oF the splice
and on a larger scale than in Figure l;
Figure 4 is a view s;milar to Figure 2 showlng one stage in the
manufacture of the splice and with the region of the splice mounted within an
injection mould; and
Figure 5 is a graph to show heat dissipation in the splice after
formation.
As shown in Figure l, a main telecommunications cable 10 has four
drop wire pairs 11, 12, 13, 14 spliced to pairs of conductors of the main
cable. For convenience in splicing, the drop wire emerges from an
encapsulation 15, two axially at each end of the encapsulation with wires at
each end diametrically offset from one another across the main cable.
Each drop wire is electrically connected to its associated pair
of main cable conductors in a manner similar to the other drop wires. Thus,
for convenience, one such connection only is described. As shown in Fi~ures 2
and 3, the drop wire 12l has its pair 16 of conductors connected to a
conventional splice connector 17. A selected pair 18 of wires from the main
cable 10 are also connected to connector 17 after emerging from a longitudinal
slit 19 in the polyethylene outer sheath 10 and metallic shea~h 22 of cable 103
A ground wire 23 from drop wire 12 is grounded to the metallic sheath of the
cable 10 by a ground clamp 24 which is attached to the sheath at one side of
the slit 19.
A layer of sealing material sealingly encloses the ground clamp
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24, the connector 17 and the ground wire 23 and bared ends of conductor pairs
16, 18. The seallin~ material also encloses the slit 1~ and ~he insulation o~
the conductor pairs 16, 1~ adjacent the bared conductor ends. ~s shown in
Figure 3, the layer of sealing material comprises overlapped ~Irappin~s 25 of
ethylene-propylene rubber sealing tape whlch extend completely around the ma~n
cable 1 along the axial region of the slit 19 so as to cover the ground clamp
24, and the ground wire 23. It also passes both under and over the insulated
ends of the drop wire 12 as shown at 2~a and 25b, the drop wire being retained
against the side of the main cable. The layer of sealing material also
comprises further overlapped wrappings 26 of ethylene-propylene ruhber sealing
tape which lie over ~rappings 25 and also cover the pair of wires 18 and lh and
the connector 17 to completely enclose the connector 17 and the bared ends o-f
the conductors of wire pairs 18 and 16. Although for convenience, the
wrapDings 25, 26 are shown as separate in Figure 3, it is to be understood that
in the finished splice, the wrappings are merged together to form the layer of
sealing material.
Around the layer of sealing material is disposed a layer 27 of
material which remains unsoftened at the heat softening temperature of the
sealing material. The layer 27 is formed from overlapped wrappings of glass
tape which completely surround the sealing ma~erial and extend axially beyond
its ends onto the outer sheath 2Q of the main cable as shown by Figures 2 and
4.
The splice is completed by ~he encapsulation 15 completely
covering the sealin~ and glass tape layers.
In the manufacture of the splice, a~ter the slit 19 is formed for
the desired length along cable 1~, the pair 18 of wires are drawn through the
slit and through a hole made in a protective tongue 28 ~hich is then inserted
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through the slit to extend beneath the metallic sheath 22 as shown in Figure 3.
The tongue 28 is m~de from polyethylene and serves to retain any filling
material such as grease within cable 10 during the encapsulation operation.
The ground clamp is then secured to the sheath 22 at one slde oF the sl~t and
the ground wire 23 is electrica11y connected to It.
The wrappings 25 of sealing tape are ~hen made while ensuring the
pairs 16 and 18 of wire extend through the wrappings. The pairs then have
insulation removed at their ends and the bared conductor ends are joined to
connector 17. The connector and the wires 16, 18 with their bared ends are
then covered by the wrappings 26 of sealing tape.
It is to be understood that the other three drop wires are
connected in a similar manner to ground clamps and their selected wires of the
cable 10.
After the layer of glass tape 27 has been added, the partly
completed splice is then located within an aluminum injection mould. In Figure
4, one mould half 29 is shown with the cable 10 extending through it. Each
mould half as in mould half 29 comprises a semi-cylindrical mould cavity 30
opening onto a planar mould surface 31 for contacting the other mould half.
The surface 31 is also formed ~ith aligned semi-cylindrical openings 30, 31 for
the main cable 10, four openings 32 for passage of drop wires, and gate
passages 33 opening into the cavity 30 centrally and adjacent each end of the
mould cavity. A centrally disposed blind passage 33a is provided for
accommodating the leading plas~ics portion from the injection moulding machine
so as to hold it a~ay from the main flow passages in case it 'nas not been
softened sufficiently for injection purposes. Also provided in surface 33 are
passages for plastic spew from the injection moulding process. The mould is
provided with water cooling passages (not shown).
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With the mould closed and substantially ssealed upon the cable 10
and drop wires 11, 12, 13, 14 and with water coolant pass;ng through the
passages provided to provide a mould temperature 3~C, the part of the cable
~ith the partly completed splice is disposed within the mould cavity as shown
in Figure 4. To centre the main cable within the cavity which is 12 inches
long or possibly longer, a spacing member 34 is disposed around the cable,
substantially midway along the cavity. The use of the spacing member 34 is the
subject of a patent application entitled "Splicing of Electrically Insulated
Cable" executed on the date of execution of this application, and in the name
of Leonard Joseph Charlebois. As described in said other application, the
material of the spacing ring 34 is compatible with the plastic material to be
injected into the mould cavity. In this instance~ the member is made from
polyethylene.
The plastics material injected into the mould cavity in this
instance is ethylene acrylic acid sold by Dow Chemical ~f Canada Limited under
product number 459. This material has an acrylic acid content of approximately
8% by weight of the total weight of the material, The temperature of the
molten plastic within the extruder is 185C. During formation of the
encapsulation 15, the polyethylene of the m~mber 34 and the outer sheath of the
cable 10 the pairs 16, 18 and the drop wires is softened by the molten e~hylene
acrylic acid to enable the two materials to form a good mechanical bond
together. Also~ the ehtylene-propylene rubber tape of the wrappings 25 and 26
are softened so as to form the sealing layer, the layer 27 preventing migration
of the ethylene propylene rubber into the encapsulation material.
The aluminum mould is sufficiently heat conductive, especially
when water cooled as in this embodiment~ to cool the surface oF the moulded
encapsulation rapidly and form a skin. As the encapsulat;on cools and shrinks,
the skin then forms a barrier to prevent air from entering the encapsulation
and forming air bubbles or pockets. The mould temperature is reduced to 27C
during cooling of encapsulant.
During cooling, the shrinkage oF the encapsulat~on compresses the
sealing tape and causes it to become shaped intimately and fluid-tightly in
sealing contact with the connection 17 and bared wire conducturs of wire pairs
16, 18. Fluid tight sealing engagement is also provided bet~Jeen the sealing
layer and the gr~und clamps and earth wires and around the outer sheath of
ln cable 10 and the insulated regions of ~ire pairs 16, 18.
Although the in~jection temperature is 185C, this temperature
does not actually reach any of the insulated wires or connected ends in the
splice to cause damage. The ethylene-propylene rubber of the sealing tape is
sufficiently non-heat conductive to prevent th;s from happening. Also, the
polyethylene tongue 28 within the slit 29 is a fur~her protection against heat
transfer to the wires within cable 10.
In an experiment performed to discover the temperatures reached
at various parts of a splice made in the above way by the sue of thermocouples
inserted into the splice, the following maximum temperatures were recorded for
an injection temperature in the extruder of 185C. At each end of slit 199
beneath the sealing layer and on the cable core temperature IA' has a maximum
o~ 72C. In the region of connector 17, i.e. between wrappings 25 and 26 -
temperature 'B' has a maximum of 95C. At each end of the encapsulation, i.e.
between the encapsulation 15 and the outer sheath 20 - temperature 'C' has a
maximum of l50C. This latter temperature was reduced to below 100C after 5
minutes by the water cooled mould.
Figure 5 shows in graph form the above temperatures A, ~, and C
from the injection stage and dur;ng cooling to show the rate of heat
dissipation from the splice.
In further tests performed upon the completed splice, no
deterioration of the electrical properties of the cables and wires were shown
to take place, thus indicating the injectlon moulding temperatures had had
little or no effect upon either conductors or insula~ion and apparently had
caused no movement in the grease because of softening w~thin cable 10.
Further, static load and impact tests which were performed showed no elec~rical
or mechanical damage. In addition, temperature cycle tests and moisture
ingress tests performed upon the splice gave satisfactory electrical resistance
results. These tests involved the immersion of the splice in water ~Jith the
cable 1n ends open at each side of the splice and with the temperature cycled
between -40C and ~60C.
In another embodiment with the same construction and method of
forming a splice, the ethylene acrylic acid was replaced by an ionized resin
sold under the trade name 'Surlyn 1702' by DuPont, similar results were
obtained~
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