U.S. patent application number 10/180008 was filed with the patent office on 2002-11-14 for termination coupling for mineral insulated cable.
Invention is credited to Dancy, Kevin Charles.
Application Number | 20020166693 10/180008 |
Document ID | / |
Family ID | 24973643 |
Filed Date | 2002-11-14 |
United States Patent
Application |
20020166693 |
Kind Code |
A1 |
Dancy, Kevin Charles |
November 14, 2002 |
Termination coupling for mineral insulated cable
Abstract
A method of terminating or joining mineral insulated cables
having metallic outer tubes that does not use brazing to fasten the
outer sleeves of the terminating coupling over the outer tubes of
the cables. Instead, the sleeves are crimped onto the tubes. The
space within the termination or joint is filled with an epoxy. A
conductive strap can be used to maintain ground continuity between
the metallic outer tubes and between the outer metallic tubes and
the sleeves.
Inventors: |
Dancy, Kevin Charles;
(Kingston, CA) |
Correspondence
Address: |
BLANK ROME COMISKY & MCCAULEY, LLP
900 17TH STREET, N.W., SUITE 1000
WASHINGTON
DC
20006
US
|
Family ID: |
24973643 |
Appl. No.: |
10/180008 |
Filed: |
June 26, 2002 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10180008 |
Jun 26, 2002 |
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09739755 |
Dec 20, 2000 |
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6437246 |
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Current U.S.
Class: |
174/76 |
Current CPC
Class: |
H01R 4/72 20130101; H05B
3/06 20130101; H05B 3/56 20130101 |
Class at
Publication: |
174/76 |
International
Class: |
H02G 003/02 |
Claims
I claim:
1. For first and second mineral insulated cables, each including an
outer metallic tube and at least one internal conductor, a
termination of one of the outer metallic tubes comprising; a
coupling including at least one crimped portion grasping the one
outer metallic tube; and an epoxy filling the interior of the
coupling; a joint between the first mineral insulated cable and the
second mineral insulated cable, wherein there is electrical
continuity between the internal conductors of the two cables; and a
connection strap electrically connecting the one outer metallic
tube to the other outer metallic tube, wherein the first and second
mineral insulated cables each have one or three or more internal
conductors.
2. The termination according to claim 1, wherein the coupling
comprises a sleeve including a larger-diameter portion and a
smaller-diameter portion at the crimped portion.
3. The termination according to claim 2, wherein said connection
strap is brazed to the sleeve.
4. The termination according to claim 2, further comprising an end
cap connected to the larger-diameter portion of the sleeve.
5. The termination according to claim 1, wherein said connection
strap is selected from the group consisting of a wire, strip,
clamp, spring, lead, cable, mesh, screw-on and clip-on device.
6. The termination according to claim 1, wherein said connection
strap is brazed to the outer metallic tubes.
7. The termination according to claim 1, further comprising a
grounding cap electrically connecting the other outer metallic tube
to the coupling adjacent thereto.
8. The termination according to claim 7, wherein said grounding cap
is one of crimped on, clipped on, clamped on and screwed on said
coupling.
9. The termination according to claim 1, further comprising a
connection strap electrically connecting the other outer metallic
tube to the coupling adjacent thereto.
10. The termination according to claim 9, wherein said connection
strap is selected from the group consisting of a wire, strip,
clamp, spring, lead, cable, mesh, screw-on and clip-on device.
11. The termination according to claim 1, wherein the coupling is
located at an end of one of the first and the second mineral
insulated cables.
12. The termination according to claim 1, wherein the coupling is
located between one end of the one outer metallic tube and the
adjacent end of the other outer metallic tube.
13. A method of terminating a first or second mineral insulated
cable, each cable including an outer metallic tube and at least one
internal conductor, the method comprising: crimping a sleeve onto
one of the outer metallic tubes; filling an interior of the sleeve
with epoxy; forming a joint between the first mineral insulated
cable and the second mineral insulated cable; establishing
electrical continuity between said internal conductors of the two
cables, wherein the first and second mineral insulated cables each
have one or three or more internal conductors; and electrically
connecting the one outer metallic tube to the other outer metallic
tube.
14. The method according to claim 13, wherein the step of crimping
comprises crimping a single end of the sleeve onto the one outer
metallic tube adjacent an end thereof, and further comprising the
steps of: vertically aligning the sleeve with an un-crimped end
upward; filing the un-crimped end with the epoxy; and waiting for
the epoxy to at least partially harden; whereby the step of filling
the interior of the sleeve with epoxy is aided by gravity.
15. The method according to claim 13, wherein the step of
electrically connecting comprises providing a connection strap and
electrically connecting one end of the connection strap to the one
outer metallic tube and the other end of the connection strap to
the other outer metallic tube.
16. The method according to claim 15, wherein the step of
electrically connecting further comprises electrically connecting
the connection strap to the sleeve.
17. The method according to claim 13, further comprising the step
of electrically connecting the other outer metallic tube to the
sleeve.
18. The method according to claim 17, wherein the step of
electrically connecting comprises providing a connection strap and
electrically connecting one end of the connection strap to the
other outer metallic tube and the other end of the connection strap
to the sleeve.
Description
REFERENCE TO RELATED APPLICATION
[0001] The present application claims the benefit of U.S. patent
application Ser. No. 09/739,755 filed Dec. 20, 2000, the disclosure
of which is hereby incorporated by reference in its entirety into
the present application.
BACKGROUND OF THE INVENTION
[0002] 1. Field of Invention
[0003] The present invention relates to termination and connection
of mineral insulated (MI) heating units and cables.
[0004] 2. Description of the Prior Art
[0005] Mineral insulated cables are used primarily as heating units
and power cables. Those cables have an outer sheathing in the form
of a metal tube, one to seven conductors, and insulation of
magnesium oxide around the conductors which insulates and also
holds the conductors in place inside the metal tube.
[0006] Sections of mineral insulated cable may be terminated,
joined to each other, or joined to non-mineral insulated cables.
For example, a mineral-insulated section of non-heating cable may
be joined to a section intended for heating; these two sections
might be identical except that the heating section has
more-resistive internal conductors.
[0007] The conventional method of terminating a mineral insulated
cable is to slide an open-ended termination fitting over the outer
metallic tube of the mineral insulated cable, fill the interior
with mineral insulation similar to that in the cable, and then
braze a cap onto the open end of the fitting.
[0008] The conventional method of making joints between two
sections of mineral insulated cable is to join the conductor wires
protruding from the ends of each of the metallic tubes, for
electrical continuity, and then complete the joint with a slide-on
coupling that is brazed onto the metal tubes. The space inside the
coupling is hollow and must be filled. That is conventionally
accomplished by drilling a small hole in the side of the coupling,
injecting additional mineral insulation to fill the void, and then
sealing the hole by brazing. The hole is typically tapped to a 6-32
NC thread into which a mating brass screw is turned. The screw is
broken off and the end is brazed over.
[0009] This process is both time-consuming and uncertain:
time-consuming because the fill hole should, for obvious reasons,
be small, and filling the entire void within is a lengthy process;
uncertain because it is nearly impossible to assure that the void
is evenly filled and packed. Gaps are liable to be left, and any
effort to pack the mineral insulation into place might shift the
conductors, putting strain on wire joints and possibly even causing
a short circuit.
[0010] In addition, the mineral insulation is usually very
hygroscopic and, inevitably, it absorbs water. The filled-in
insulation must then be dried prior to sealing the hole, and that
requires great care.
[0011] Not only the after-filling, but the brazing of the couplings
to the tubes, is likewise time-consuming. Thorough cleaning of the
tubes and couplings is needed and all oxide must be removed, or
else the joint will not be satisfactory.
[0012] Brazing involves high temperatures that alter the physical
properties of the metal in the tubes, making them brittle and
leading to increased liability to cracking and a larger permissible
bend radius. It also causes new oxidation, which must be removed.
In addition, brazing creates unhealthy fumes.
[0013] The prior art does not disclose any method of terminating
(capping or joining) sections of mineral-insulated cable which is
fast, insures uniform filling of voids between internal conductors,
does not require cleaning of oxide or corrosion from metal
surfaces, and which does not harm cables through high
temperature.
SUMMARY AND OBJECTS OF THE INVENTION
[0014] In view of the foregoing, it should be apparent that there
still exists a need in the art for an apparatus and method of
terminating a mineral insulated cable that overcomes the problems
of the prior art. Accordingly, it is a primary objective of the
present invention to terminate or join sections of mineral
insulated cable quickly and reliably; to insure the absence of
voids in joined or terminated sections of mineral insulated cable;
to eliminate the cleaning of oxide or corrosion from metal
surfaces; to keep metal parts below temperatures at which
embrittlement occurs; and to avoid the production of unhealthy
fumes.
[0015] Briefly described, these and other objects of the invention
are accomplished in accordance with its apparatus aspects by
providing one or more mineral insulated cables and a sleeve that is
crimped to the termination of one of the mineral insulated cables,
the sleeve being filled with epoxy potting. If the termination is
between two cables, then the outer metallic sleeves of the cables
are electrically grounded together using a connection strap and the
conductors are brazed together. The sleeve may be electrically
connected to one or both of the outer metallic tubes by a cap or a
connection strap. The cap may also be electrically connected to one
of the outer metallic tubes using a connection strap. The types of
connections straps include, but are not limited to, wires, strips,
clamps, springs, leads, cables, meshes, screw-on or clip-on
devices.
[0016] The method of the present invention is carried out by
reducing or eliminating brazing from the processes of joining two
sections of mineral insulated cable or of terminating an end of a
section of mineral insulated cable. In the present invention,
couplings are joined to tubes by crimping, and voids are filled
with epoxy, the internal conductors are brazed together and the
outer metallic tubes of the two cables are electrically coupled.
Further, a cap may be screwed-on or clamped on the open end of the
sleeve after the epoxy sets and a connection strap electrically
connecting the cap to one of the outer metallic tubes may added.
That method of terminating mineral insulated cables is faster and
more certain than the prior-art methods, does not harm the metal of
the tubes, requires a lower level of skill, and eliminates the need
for drilling holes in coupling sleeves and end cap fittings.
[0017] The present invention may be assembled or made either in a
factory or in the field.
[0018] With these and other objects, advantages and features of the
invention that may become hereinafter apparent, the nature of the
invention may be more clearly understood by reference to the
following detailed description of the invention, the appended
claims and to the several drawings attached herein.
BRIEF DESCRIPTION OF THE DRAWINGS
[0019] FIG. 1 is a plan view of the invention showing two mineral
insulated cables and terminations at the ends and between the
cables;
[0020] FIG. 2 is a detailed, partially cut-away, view of the
invention according to FIG. 1;
[0021] FIG. 3 is a detailed, partially cut-away, view of the
invention according to FIG. 1;
[0022] FIG. 4 is a detailed, partially cut-away, view of the
invention according to FIG. 1;
[0023] FIG. 5 is a cross-sectional view of section V-V of FIG.
1;
[0024] FIG. 6 is a detailed, partially cut-away, view of the
invention shown in FIG. 3 but with an alternative grounding strap
shown;
[0025] FIG. 7 is a detailed, partially cut-away, view of the
invention shown in FIG. 3 but with an alternative screwed on
grounding cap shown;
[0026] FIG. 8 is a detailed, partially cut-away, view of the
invention shown in FIG. 3, but with an alternative clamped on mesh
grounding cap shown; and
[0027] FIG. 9 is a detailed, partially cut-away, view of the
invention shown in FIG. 3, but with an alternative spring-fit
grounding cap shown.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0028] Referring now to the drawings wherein like elements are
identified by like reference numerals, there is shown in FIG. 1 a
mineral insulated cable 100 of the "D" design type, the type which
is exemplary in this application. Multiple external-power
connection wires 105a, 105b, . . . 105f . . . 105n, where n is
greater than 1, extend from one end of the mineral insulated cable
100 for connection to a power source. There may be any number of
conductors 105n but it is preferred that the number of conductors
105n be less than eight (that is, n<8) and ideally less than
four (that is, n<4).
[0029] A first coupling 120 couples the wires 105n to a power lead
130 of the cable 100, which is joined by a second coupling 140 to a
heating element 150 terminated by a cap 160. The power lead 130 and
the heating element 150 are similar in structure, differing mainly
in what type of conductive wires 135n, 155n are enclosed in them
(see FIG. 3). Their common structure is shown in FIG. 5. It is
noted that the invention does not require similarity of
structure.
[0030] In this disclosure, "termination" includes the structure at
the end of a single cable section as well as a joint between two
cables.
[0031] FIG. 5 is a nominal cross section of the power lead 130, but
includes reference numerals for elements of the heating element 150
to simplify the drawing. Each section includes a metallic outer
tube 132 (of the power lead) or 152 (of the heating element), a
filling of mineral insulation 180, and inner conductors 135n or
155n. The inner conductors may be of low resistance (135n, power
lead) or of high resistance (155n, heating element).
[0032] FIG. 2 shows in detail the termination or coupling 120 at
which the external power wires 105n are joined to the power lead
130. The wires 105n may be extensions of the conductors 135n
running through the power lead 130 (as best seen in FIG. 5), or
alternatively there may be a brazed joint 123 between each
conductor 135n and its respective external connection wire 105n. If
the conductors 135n and/or the wires 105n are insulated wires, then
an insulating sleeve like shrink tubing (not shown) can be applied
to cover the bare joint.
[0033] The first termination or coupling 120 is preferably a sleeve
of generally constant diameter prior to being crimped onto the
outer tube of the cable 130, after which the smaller-diameter
crimped portion 122 grips the tube 132 of the power lead 130. The
un-crimped portion 124, which contains the tube 132 (if any), is of
larger diameter.
[0034] The preferred material for the sleeve is free-machining
brass. One example of a preferred crimping tool is Thomas and Betts
model TBM-25S.
[0035] There is no need for any additional mineral insulation to be
inserted into the un-crimped portion 124. That space is filled with
an epoxy 180, that seals the end of the mineral insulated cable 100
without the need for any cap, tamping, or brazing. However, a cap
could be used, if desired. The epoxy seeps into any gaps between
the tube 132 and the crimped portion 122 of the termination
120.
[0036] The preferred type of epoxy 180 is potting epoxy which is
capable of withstanding high voltages and high temperatures. One
example of a preferred epoxy is DURALCO 4525 made by Cotronics of
Brooklyn, N.Y.
[0037] FIG. 3 illustrates the coupling 140 between the power lead
130 and the heating element 150. A preferably brazed connection 143
joins each pair of corresponding low- and high-resistance
conductors 135n and 155n. A large-diameter sleeve 144 is crimped at
one end to form a reduced-diameter portion 142, which grips the
tube 152 of the heating element 150. The gap between the tubes 152
and 132 and the space inside the sleeve 144 is filled with epoxy
180.
[0038] Preferably, the cable is assembled in a vertical orientation
with the crimped portions 122, 142, and 162 (FIG. 4) downward. The
epoxy 180 fills the upper open end of the sleeve 120, 140, or 160
(FIG. 4), flows downward to fill the cavity, and sets. That seals
the conductors within and mechanically joins the tubes 132, 152
into a solid unit.
[0039] However, in many cases it is preferable to connect the two
tubes 132 and 152 electrically and well as mechanically, for
example where the tube 152 acts as a ground element. To do that, a
connection strap or grounding wire 325 (FIG. 1) is used to connect
the two tubes and is preferably brazed to the tubes 132, 152, and
optionally to the sleeve 140 as shown in FIG. 1. The wire or strap
325 may be spot-brazed as shown, either before or after filling the
sleeve 140 with the epoxy 180.
[0040] A similar connecting wire or strap may optionally connect
the tube 132 to the sleeve 120 or an adjacent metallic structure
(not shown).
[0041] Here, and in the following figures and claims, "connection
strap" includes any wire, strip, clamp, spring, lead, cable, mesh,
screw-on or clip-on device, or any other conductive element.
[0042] FIG. 6 shows that the grounding strap 325 may also be
internal to the tubes 132, 152. In this embodiment the strap 325
may be brazed in place before filling the sleeve 144 with the epoxy
180.
[0043] FIG. 7 shows an embodiment in which the grounding strap 325
is replaced with a grounding end cap 327. The grounding cap 327 may
be crimped, clipped, or clamped onto the sleeve 144 or screwed on
with threads. As shown in FIG. 7, one end of the end cap 327 is
screwed on the sleeve 144 and the other end is crimped on the tube
132.
[0044] FIG. 8 shows an embodiment in which the grounding cap 327 is
replaced with a electrically-conducting mesh 328 which is clamped
on the sleeve 144 and tube 130 using clamps 330. The clamps 330
could also be used to secure the grounding cap 327 shown in FIGS. 7
and 9 to the sleeve 144 and tube 130.
[0045] FIG. 9 shows an embodiment in which the grounding cap 327 is
clipped on or held on using a spring 329. In this case, the cap 327
would clip to the sleeve 144 at one or more suitable friction
contact points in opposition to the force of the spring pushing
against the cap 327 or, the spring could be biased to hold the cap
327 onto the sleeve 144.
[0046] FIG. 4 shows the termination 160. The two heating-element
wires 155n are (preferably) brazed together at one or more joints
163, and a sleeve 164 is crimped over the tube 152.
[0047] Although only preferred embodiments of the invention are
specifically illustrated and described herein, it will be
appreciated by one of ordinary skill in the art that many
modifications and variations of the present invention are possible
in light of the above teachings and within the purview of the
appended claims without departing from the spirit and intended
scope of the invention.
* * * * *