Note: Descriptions are shown in the official language in which they were submitted.
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TENSION-RESISTANT CONNECTION BETWEEN A SHIELDED
HEATING CABLE AND A POWER SUPPLY CABLE
FIELD OF THE INVENTION
The present invention relates to a tension-resistant electrical and
mechanical connection between multi-conductor cables.
BACKGROUND OF THE INVENTION
United States patent No. 2,452,823 granted to Wright on November 2"d,
1948 describes a splice between free ends of two shielded cables. More
specifically, the two cables each comprise multiple current-carrying
conductors
enclosed within a wire braid.
The cable splice of Wright requires stripping of the insulation from the
free ends of the conductors. Each pair of conductors from the two cables are
connected by means of a splicing tube and then individually insulated. A
braided wire sleeve. is then drawn over the spliced portion of the conductors.
The sleeve is then extended longitudinally to cause it to engage the splice,
and
is then lashed firmly in place with a lashing wire. Finally, the sleeve is
securely
lashed to portions of the wire braids and connects them mechanically.
The cable splice of United States patent No. 2,452,823 is not only
complex but does not allow the wire braids of the two cables to efficiently
and
totally support a longitudinal tension applied to the cable splice.
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SUMMARY OF THE INVENTION
The present invention relates to a method of electrically and
mechanically connecting (a) a first shielded cable comprising a metal sheath
and electrical conductors with (b) a second cable comprising a ground
conductor and electrical conductors. The method comprises:
connecting, in a zone of interconnection between the first and second
cables, a free end of the metal sheath with a free end of the ground
conductor;
connecting, in the interconnection zone, free ends of the electrical
conductors of the first cable with free ends of the electrical conductors of
the
second cable, respectively; and
making, in the interconnection zone, a length of the interconnected
metal sheath and ground conductor shorter than lengths of the interconnected
electrical conductors of the first cable and electrical conductors of the
second
cable whereby, in operation, longitudinal tension in the interconnection zone
is
totally supported by the interconnected metal sheath and ground conductor.
The present invention also relates to an electrical and mechanical
connection between (a) a first shielded cable comprising a metal sheath and
electrical conductors and (b) a second cable comprising a ground conductor
and electrical conductors. The electrical and mechanical connection
comprises:
a zone of interconnection between the first and second cables;
in the interconnection zone, a first connection between a free end of the
metal sheath and a free end of the ground conductor; and
in the interconnection zone, second connections between free ends of
the electrical conductors of the first cable and free ends of the electrical
conductors of the second cable, respectively;
In the interconnection zone, the interconnected metal sheath and
ground conductor have a first length shorter than second lengths of the
interconnected electrical conductors of the first cable and electrical
conductors
of the second cable whereby, in operation, longitudinal tension in the
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interconnection zone is totaNy supported by the interconnected metal sheath
and ground conductor.
The present invention further relates to a method of electrically and
mechanically connecting (a) a shielded heating cable comprising a metal
sheath and heating wire elements with (b) a power supply cable comprising a
ground conductor and power supply conductors. The method comprises:
connecting, in a zone of interconnection between the shielded heating
cable and the power supply cable, a free end of the metal sheath with a free
end of the ground conductor;
connecting, in the interconnection zone, free ends of the heating wire
elements with free ends of the power supply conductors, respectively; and
making, in the interconnection zone, a length of the interconnected
metal sheath and ground conductor shorter than lengths of the interconnected
heating wire elements and power supply conductors whereby, in operation,
longitudinal tension in the interconnection zone is totally supported by the
interconnected metal sheath and ground conductor.
The present invention still further relates to an electrical and
mechanical connection between (a) a shielded heating cable comprising a
metal sheath and heating wire elements and (b) a power supply cable
comprising a ground conductor and power supply conductors. The electrical
and mechanical connection comprises:
a zone of interconnection between the shielded heating cable and the
power supply cable;
in the interconnection zone, a first connection between a free end of the
metal sheath and a free end of the ground conductor; and
in the interconnection zone, second connections between free ends of
the heating wire elements and free ends of the power supply conductors,
respectively.
In the interconnection zone, the interconnected metal sheath and
ground conductor have a first length shorter than second lengths of the
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interconnected heating wire elements and power supply conductors whereby,
in operation, longitudinal tension in the interconnection zone is totally
supported by the interconnected metal sheath and ground conductor.
The foregoing and other objects, advantages and features of the
present invention will become more apparent upon reading of the following
non-restrictive description of illustrative embodiments thereof, given by way
of
example only with reference to the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
In the appended drawings:
Figure 1 is a side elevational view of a non-restrictive illustrative
embodiment of the present invention, showing an interconnection zone
between a shielded heating cable and a power supply cable.
DETAILED DESCRIPTION OF THE ILLUSTRATIVE EMBODIMENT
The non-restrictive illustrative embodiment of the method and
connection according to the present invention, for electrically and
mechanically
connecting a shielded heating cable with a power supply cable will now be
described with reference to Figure 1.
Although the present invention will be described in relation to
connection of a shielded heating cable with a power supply cable, it should be
kept in mind that it is within the scope of the present invention to apply the
same concept to other types of multi-conductor cables.
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Shielded heating cable 1
Referring to Figure 1, the shielded heating cable, generally identified by
the reference 1 comprises:
5 - a pair of spirally twisted heating wire elements 11 and 12;
- a metal sheath 13 enclosing the pair of spirally twisted heating wire
elements 11 and 12; and
- an insulating jacket 14 covering the metal sheath 13.
Heating wire element 71
The heating wire element 11 comprises a resistance wire 111 covered
with insulation 112.
The resistance wire 111 has an electrical resistance (resistance by unit
of length of resistance wire) dependent on the diameter of the wire 111. More
specifically, the electrical resistance of the resistance wire 111 is
adjusted,
taking into consideration the total length of the heating wire element 11 in a
typical installation, to release a given amount of heat when supplied with
alternating current from, for example, a 120-Volt 60-Hz voltage source
commonly found in residential, industrial and commercial buildings.
The resistance wire 111 can be made of copper, or another electrically
conductive material, for example an electrically conductive metal other than
copper, or an electrically conductive metal alloy including copper and/or any
other suitable metal(s).
The insulation 112 of the heating wire element 11 can be made of
extruded plastic material such as polyethylene or polypropylene capable of
withstanding and conducting the heat generated by and released from the
resistance wire 111.
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Heating wire element 12
In the same manner, the heating wire element 12 comprises a
resistance wire 121 covered with insulation 122.
The resistance wire 121 has an electrical resistance (resistance by unit
of length of resistance wire) dependent on the diameter of the wire 121. More
specifically, the electrical resistance of the resistance wire 121 is
adjusted,
taking into consideration the total length of the heating wire element 12 in a
typical installation, to release a given amount of heat when supplied with
alternating current from, for example, a 120-Volt 60-Hz voltage source
commonly found in residential, industrial and commercial buildings.
The resistance wire 121 can be made of copper, or another electrically
conductive material, far example an electrically conductive metal other than
copper, or an electrically conductive metal alloy including copper and/or any
other suitable metal(s).
The insulation 122 of the heating wire element 12 can be made of
extruded plastic material such as polyethylene or polypropylene capable of
withstanding and conducting the heat generated by and released from the
resistance wire 121.
The heating wire elements 11 and 12 are spirally twisted with a given
lay, this lay corresponding to the length required by the heating wire
elements
11 and 12 to be spirally twisted by 1 turn. An advantage is that, by spirally
twisting the heating wire elements 11 and 12, the electromagnetic field from
the heating wire element 11 and the electromagnetic field from the heating
wire element 12 substantially cancel each other, of course when the current
has the same given amplitude in the two heating wire elements 11 and 12, and
the current flowing through the heating wire element 11 flows in a direction
opposite to the current flowing through the heating wire element 12.
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Metal sheath 13
The metal sheath 13 is formed of a plurality of small-diameter copper
wires braided together to form a tubular shielding andlor a metal tape
spirally
wound or longitudinally applied. The main function of the metal sheath 13 is
to
ground the heating cable 1 through a connection to the ground. The metal
sheath i 3 is also designed to resist to impacts as strong as 100 Ibs.
Of course, the metal sheath 13 will comprise braided wires andlor tape
made of an electrically conductive material capable of withstanding and
conducting the heat generated by and released from the resistance wires 111
and 121. Although this material could be copper, it is within the scope of the
present invention to use another electrically conductive material, for example
an electrically conductive metal other than copper, or an electrically
conductive
metal alloy including copper and/or any other suitable metal(s).
Insulating jacket 14
The insulating jacket 14 covering the metal sheath 13 can be made of
extruded plastic or elastomeric material with or without subsequent cross-
linking such as polyethylene or polypropylene capable of withstanding and
conducting the heat generated by and released from the resistance wires 111
and 121.
Power supply cable 2
Still referring to Figure 1, the power supply cable, generally identified by
the reference 2, comprises:
- an insulated ground conductor 22;
- two insulated electrical conductors 21 and 23; and
- an insulating jacket 24 enclosing the three insulated conductors 21, 22
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and 23.
Insulated electrical conductor 21
The insulated electrical conductor 21 comprises an electrically
conductive wire 211 covered with insulation 212. The electrically conductive
wire 211 can be made of copper, or of another electrically conductive
material,
for example an electrically conductive metal other than copper, or an
electrically conductive metal alloy including copper and/or any other suitable
metal(s). The insulation 212 of the insulated electrical conductor 21 can be
made of extruded plastic material such as polyethylene or polypropylene.
Insulated ground conductor 22
The insulated ground conductor 22 comprises an electrically conductive
wire 221 covered with insulation 222. The electrically conductive wire 221 can
be made of copper, or of another electrically conductive material, for example
an electrically conductive metal other than copper, or an electrically
conductive
metal alloy including copper and/or any other suitable metal(s). The
insulation
222 of the insulated ground conductor 22 can be made of extruded plastic
material such as polyethylene or polypropylene.
Insulated electrical conductor 23
The insulated electrical conductor 23 comprises an electrically
conductive wire 231 covered with insulation 232. This electrically conductive
wire 231 can be made of copper, or of another electrically conductive
material,
for example an electrically conductive metal other than copper, or an
electrically conductive metal alloy including copper andlor any other suitable
metal(s). The insulation 232 of the insulated electrical conductor 23 can be
made of extruded plastic material such as polyethylene or polypropylene.
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Insulating jacket 24
The insulating jacket 24 enclosing the three insulated conductors 21-23
can be made of extruded plastic or elastomeric material with or without
subsequent cross-linking such as polyethylene or polypropylene.
Electrical and mechanical connection
To electrically and mechanically connect a free end 15 of the shielded
heating cable 1 to a free end 25 of the power supply cable 2, the following
operations are conducted:
- the insulating jacket 14 is stripped from the free end 15 of the shielded
heating cable 1 to expose a free end of the metal sheath 13;
- the heating wire elements 11 and 12 are withdrawn from the exposed free
end of the metal sheath 13;
- the insulation 112 is stripped from the free end of the heating wire element
11 to expose a free end 113 of the resistance wire 111;
- the insulation 122 is stripped from the free end of the heating wire element
12 to expose a free end 123 of the resistance wire 121;
- the insulation 212 is stripped from the free end of the power supply
conductor 21 to exposed a free end 213 of the electrically conductive wire
211;
- the insulation 222 is stripped from the free end of the ground conductor 22
to exposed a free end 223 of the electrically conductive wire 221;
- the insulation 232 is stripped from the free end of the power supply
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conductor 23 to expose a free end 233 of the electrically conductive wire
231;
- the free end 223 of the electrically conductive wire 221 of the ground
5 conductor 22 is ultrasonically welded to the free end of the metal sheath 13
corresponding to the stripped free end 15 of the shielded heating cable;
- the free ends 113 and 213 are ultrasonically welded; and
10 - the free ends 123 and 233 are ultrasonically welded.
As illustrated in Figure 1, in a zone 3 of interconnection between the
shielded heating cable 1 and the power supply cable 2, the interconnected
metal sheath 13 and ground conductor 22 have a length shorter than a length
of the interconnected heating wire element 11 and power supply conductor 21.
Also, the interconnected metal sheath 13 and ground conductor 22 have, in
the zone 3, a length shorter than a length of the interconnected heating wire
element 12 and power supply conductor 23. In this manner, in operation,
longitudinal tension in the interconnection zone 3 is totally supported by the
interconnected metal sheath 13 and ground conductor 22.
Since the heating wire elements 11 and 12 have small-diameter, fragile
resistance wires 111 and 121, the construction illustrated in Figure 1 will
protect the resistance wires 111 and 121 from rupture or other damage caused
by tension in the interconnection zone 3 of the cables 1 and 2.
The loop made with each of the resistance wires 111 and 121 at the
point of connection between the shielded heating cable 1 and the power
supply cable 2 also provides room to relieve the stress caused by the thermal
expansion of the resistance wires 111 and 112 when electrical power is
applied. The resistance wires 111 and 121 having a diameter much smaller
than the electrically conductive wires 211 and 231 of the power supply cable 2
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(non-heating cable), without these loops, all of the expansion stress would be
localized at the weakest points of the resistance wires 111 and 121, which
would be the points just next to the respective connections with the
electrically
conductive wires 211 and 231 of the power supply cable 2. Without the loops,
there would be a higher probability of having power interruptions due to the
breakage of the resistance wires 111 and 121 at these particular points.
Although the non-restrictive illustrative embodiment of the present
invention has been described in relation to ultrasonic welding of the wires
and
sheath, it should be kept in mind that it is within the scope of the present
invention to use other types of welding as well as other types of connections.
Also, the interconnected heating wire element 11 and power supply
conductor 21 can form a 360°- loop (not shown} in the interconnection
zone 3.
The free wire ends 113 and 213 can then be placed side by side in the
continuity of both the heating wire element 11 and power supply conductor 21
and ultrasonically welded in this position.
In the same manner, the interconnected heating wire element 12 and
power supply conductor 23 can form a 360° loop (not shown) in the
interconnection zone 3. The free wire ends 123 and 233 can then be placed
side by side in the continuity of both the heating wire element 12 and power
supply conductor 23 and ultrasonically welded in this position.
Finally, the interconnected wire free end 223 and metal sheath free
end, the interconnected free ends 113 and 213, and the interconnected free
ends 123 and 233 are individually insulated using conventional techniques well
known to those of ordinary skill in the art. In the same manner the
individually
insulated interconnected wire free end 223 and metal sheath free end,
interconnected free ends 113 and 213, and interconnected free ends 123 and
233 are finally globally covered with additional insulation, for example a
heat-
shrinkable jacket covering the interconnection zone 3 and adjacent portions of
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the insulating jackets 14 and 24.
Although the present invention has been described hereinabove by way
of a non-restrictive illustrative embodiment thereof, this embodiment can be
modified at will, within the scope of the appended claims, without departing
from the spirit and scope of the present invention.
