Jointing or terminating plastics sheathed electric cable

In effecting a fluid-tight seal between a plastics part of a cable joint or termination enclosure and the plastics sheath of an electric cable a hole is formed in the wall of said part to form a cable entry of a size appropriate to the cable and a length of the cable is passed through the cable entry so formed. A mould is assembled about the cable adjacent a surface of said part, which mould embraces the cable and has ports for the admission and discharge of molten thermoplastics material, and the mould is temporarily secured to said part of the enclosure. Molten thermoplastics material is injected into the interior of the mould through said admission port and, after a sufficient quantity of molten thermoplastics material has passed through the mould and out of the discharge port to soften the surfaces of the cable sheath and said part of the enclosure, the mould is sealed and the molten thermoplastics material in the mould is permitted or caused to cool and make an effective bond with the cable sheath and with said part of the enclosure.

This invention relates to jointing or terminating electric cables insulated 
or sheathed with thermoplastics material and is particularly concerned 
with electric cable joints or terminations of the kind in which the 
connections between cable conductors or the terminated end of a cable are 
or is surrounded by a joint enclosure that makes a fluid-tight joint with 
the thermoplastics sheath, insulation or other covering of each cable 
connected at the joint or of the or each cable at the termination. The 
sheath, insulation or other covering of cable with which an enclosure 
makes a fluid-tight joint is hereinafter included in the term "sheath". 
According to the present invention we provide a method of making a joint 
between plastics sheathed cables, or a termination of a plastics sheathed 
cable, of the kind in which connections between the cable conductors or 
the terminated end of the or each cable conductor are or is surrounded by 
a joint or termination enclosure divided transversely of the axis of at 
least one of the cables into at least two separately formed parts secured 
together in a fluid-tight manner, at least one of said separately formed 
parts of the enclosure being of plastics material and being sealed in a 
fluid-tight manner to the plastics sheath of the cable or at least one of 
the cables, wherein the fluid-tight seal between said part of the 
enclosure and the cable sheath is effected by cutting or otherwise forming 
a hole in the wall of said part to form a cable entry of a size 
appropriate to the cable; passing a length of the cable through the cable 
entry so formed; assembling about the cable adjacent a surface, preferably 
the outer surface, of said part a mould which embraces the cable and has 
ports for the admission and discharge of molten thermoplastics material; 
clamping or otherwise temporarily securing the mould to said part; 
injecting into the interior of the mould through said admission port 
molten thermoplastics material that is compatible with the plastics 
materials of the cables sheath and of said part of the enclosure and that 
is at a temperature appreciably above the softening point of said 
materials; and, after a sufficient quantity of molten thermoplastics 
material has passed through the mould and out of the discharge port to 
soften the surfaces of the cable sheath and said part of the enclosure, 
sealing the mould, and permitting or causing the molten thermoplastics 
material in the mould to cool and make an effective bond with the cable 
sheath and with said part of the enclosure. 
Preferably after sealing the mould the volume of the sealed space within 
the mould is reduced, for instance by means of a plunger connected to at 
least one of the ports in the mould, to compensate for contraction of the 
thermoplastics material on cooling. In some cases the source of supply can 
be used for this purpose but preferably the source of supply of molten 
thermoplastics material is disconnected from the mould before the mould is 
sealed. 
By a plastics material that is compatible with the plastics material of the 
sheath is meant a material that will make an effective bond with, and will 
not have any deleterious effect on, the material of the sheath, or vice 
versa. 
The joint or termination enclosure is preferably of elongate form and the 
part of the enclosure in which the hole to form the cable entry is cut or 
otherwise formed is preferably a separately formed end wall of the 
elongate enclosure. Preferably the surface of the end wall against which 
the mould is clamped is of planar form and preferably this planar surface 
lies in a plane that will be radial to the axis of a cable passing through 
the cable entry. 
The method of the present invention is especially, but not exclusively, 
suitable for use when it is required to connect a cable to an existing 
joint between at least two cables, or to an existing termination of a 
cable, for example in a local telephone cable network where it is required 
to connect an additional cable to an existing telephone cable 
installation. In this case the joint or termination enclosure is opened up 
to expose the existing joint or termination, a hole is cut or otherwise 
formed in an end wall or other part of the enclosure, a length of the 
additional cable is passed through the cable entry so formed and its 
conductor or conductors is or are connected to a conductor or conductors 
of one or more of the cables or of the cable of the existing joint or 
termination, the cable is then sealed to the end wall or other part of the 
enclosure by the method as hereinbefore described, and the enclosure is 
then re-closed. 
The invention also includes, for use in the method as hereinbefore 
described, a tubular mould having ports for the admission and discharge of 
molten thermoplastics material, which mould is divided longitudinally into 
at least two separately formed parts which together define, at one end of 
the mould, a bore of a shape and size complementary to those of the sheath 
of a cable to be jointed and, at the other end of the mould for engaging 
an end wall or other part of the joint enclosure, an annular surface which 
extends transversely of the axis of the mould and whose radially inner 
boundary is spaced radially outwardly of the internal surface of said 
bore. 
Preferably said annular surface lies in a plane substantially normal to the 
axis of the tubular mould. The mould preferably consists of two separately 
formed parts, the port for admission of thermoplastics material being in 
one part and the port for discharge of thermoplastics material being in 
the other part. 
To reduce the risk that transfer of heat from the mould to that part of the 
end wall or other part of the enclosure engaged by the or each clamp will 
so soften said part that deformation of the end wall may occur, a layer of 
thermal insulating material may be inserted between said annular surface 
of the mould and the surface of the end wall or other part of the 
enclosure against which the mould is to be clamped. 
With a view to ensuring that the clamping force employed when the mould is 
temporarily secured to the end wall or other part of the enclosure is 
distributed over a substantial proportion of the internal surface of the 
end wall or other part of the enclosure, at least one apertured metal 
plate divided transversely into two parts is preferably clamped against 
said internal surface. If desired, a pair of apertured metal plates 
transversely divided into two parts and arranged face-to-face may be 
employed to distribute the clamping force, for example each of the pair of 
plates comprising two semi-annular parts, and one or each of the abutting 
surfaces of the pair of plates may have upstanding pins which engage in 
complementary-shaped holes in the other of the abutting surfaces to locate 
one of the pair of two-part plates with respect to the other, preferably 
in such a way that the diametrically extending edges of one of the pair of 
two-part plates are substantially normal to the diametrically extending 
edges of the other pair of two-part plates. 
In a first alternative arrangement, a plate of metal or of other suitable 
reinforcing material may be embedded in, or secured to the internal 
surface of, the end wall or other part of the enclosure to ensure that the 
clamping force is distributed over a substantial proportion of the end 
wall or other part of the enclosure. Where the end wall or other part of 
the enclosure has a peripheral wall to which, say, a joint sleeve may 
subsequently be bonded, this peripheral wall may have a ring of metal, or 
other suitable reinforcing material, embedded in it or secured to its 
internal surface. 
In a second alternative arrangement a tubular member, having a relatively 
thick wall and divided longitudinally into at least two parts, is applied 
about the cable to be jointed on the side of the end wall or other part of 
the enclosure remote from the mould and is clamped against the end wall or 
other part of the enclosure by a clamp or clamps engaging the end of the 
tubular member remote from the end wall or other part of the enclosure. 
The end face of the tubular member may have blind holes or may be 
otherwise shaped to assist in location of the clamp or clamps. Tne parts 
of the tubular member may be secured together by at least one 
circumferential clip which may engage in an annular groove in the tubular 
member. Where the end wall or other part of the enclosure has a peripheral 
wall extending lengthwise along the enclosure, to facilitate clamping of 
the mould the tubular member preferably has a length greater than that of 
the peripheral wall. 
The or each clamp employed to secure the mould to the external surface of 
the end wall or other part of the enclosure may also serve to locate the 
mould with respect to the end wall, or other part of the enclosure, by 
means of upstanding pins and/or holes on or in the parts of the or each 
clamp which abut the remote surfaces of the mould and end wall or other 
part of the enclosure, which pins engage in complementary-shaped holes in, 
and/or which holes are engaged by complementary-shaped upstanding pins on, 
said remote surfaces.

The existing straight joint between the two plastics sheathed telephone 
cables is housed in a joint enclosure of thermoplastics material which is 
divided transversely of the cable axes into three separately formed parts 
consisting of two substantially identical end parts sealed to the plastics 
sheaths of the jointed cables and a central sleeve extending between and 
sealed to the end parts. In order to connect the additional telephone 
cable to the existing joint the seals between the central sleeve and the 
end parts are broken and the sleeve is drawn back over the end part 
opposite to that through which the additional cable is to be passed so 
that the existing conductor joints are exposed. 
As will be seen on referring to the drawing, a hole 2 is now cut in the end 
wall 1 of the other end part, a length of the additional telephone cable C 
is passed through the cable entry so formed and the conductors of the 
cable are connected to conductors of the cables of the existing joint. A 
seal is now effected between the cable C and the end wall 1. To this end a 
convolute wrapping 3 of tape is built up on the cable C at a predetermined 
distance from the desired position of the end wall on the cable and a 
two-part tubular mould 4 having at one end a bore 5 and, at the other end, 
a radially extending annular surface 6 is applied to the cable with the 
convolute wrapping 3 of tape positioned in the bore. One part of the mould 
4 has an inlet port 7 and the other part of the mould has an outlet port 
8. The end wall 1 is now positioned to abut the annular surface 6 of the 
mould and, in the case where the mould is of metal or other material of 
high thermal conductivity, a layer 9 of thermal insulating material is 
interposed between the annular surface and the external surface of the end 
wall. A pair of two-part annular metal plates 10 are applied to the 
internal surface of the end wall 1, a convolute wrapping 11 of tape having 
previously been applied to the cable adjacent the internal surface of the 
end wall to fill the space between the cable and the radially inner 
boundary of the metal plates. The mould 4 is clamped to the end wall 1 by 
a clamp 12, the metal plates 10 serving to distribute the clamping force 
over a substantial proportion of the internal surface of the end wall. 
Molten thermoplastics material identical with the plastics material of the 
cable sheath and joint enclosure and at a temperature appreciably above 
their softening temperatures is now injected into the interior of the 
mould 4 through the inlet port 7 and is allowed to flow out of the outlet 
port 8 until a sufficient quantity of molten thermoplastics material has 
passed through the mould and out of the port 8 to soften the surfaces of 
the cable sheath and the part of the end wall within the mould. During 
this operation the layer 9 of thermal insulating material reduces the risk 
that heat will be transferred from the mould to that part of the end wall 
engaged by the clamp which will so soften that deformation of the end wall 
may occur. The convoluted wrapping 11 of tape prevents collapse of the end 
wall 1 in the gap between the cable and the radially inner edges of the 
metal plates 10 during the moulding process. 
The source of supply of molten thermoplastics material is now disconnected 
from the mould, plungers (not shown) are secured to the admission and 
discharge ports and the molten thermoplastics material in the mould is 
permitted to cool and make an effective joint with the cable sheath and 
with the end wall, the volume of the mould being gradually reduced by 
means of the plungers during the cooling period to compensate for 
contraction of the thermoplastics material on cooling. Alternatively, a 
plunger used to force molten thermoplastics material into the mould may be 
used to reduce the volume of the mould. 
The clamp 12 is now removed, the mould 4 and metal plates 10 are removed 
and the central sleeve of the joint enclosure slid back in place and 
re-sealed to the end parts of the enclosure.