U.S. patent number 3,576,941 [Application Number 04/847,937] was granted by the patent office on 1971-05-04 for flat power-distribution cable.
This patent grant is currently assigned to International Business Machines Corporation. Invention is credited to Donald F. Colglazier.
United States Patent |
3,576,941 |
Colglazier |
May 4, 1971 |
FLAT POWER-DISTRIBUTION CABLE
Abstract
A flat cable for distributing electrical power between hingeable
or demountable pieces of electrical apparatus is made up of thin,
flat conductors nonrigidly mounted one on top of the other. The
nonrigid mounting of the conductors relative to each other permits
one to slip or slide relative to the other and thereby improve
flexure of the cable and also increase the number of flexures the
cable can be cycled through before it fails. Nonrigid mounting can
be achieved by several different configurations. First, each flat
conductor can be provided with its separate insulating layer and
then the two insulated conductors may be held one over the other
loosely so that they may slide or slip relative to each other.
Second, a flat insulating cable may have a partition across its
width so that one flat conductor may be placed in one partitioned
section and the other flat conductor may be placed under the other
conductor in the second partitioned section. Third, separately
insulated conductors may be taped together at spaced locations so
as to allow each conductor to slide within its own insulation and
to allow relative movement of the conductors between the spaced
locations.
Inventors: |
Colglazier; Donald F.
(Rochester, MN) |
Assignee: |
International Business Machines
Corporation (Armonk, NY)
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Family
ID: |
25301884 |
Appl.
No.: |
04/847,937 |
Filed: |
August 6, 1969 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
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699595 |
Jan 9, 1968 |
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Current U.S.
Class: |
174/117FF;
174/113R |
Current CPC
Class: |
H01B
7/0045 (20130101); H01B 7/0838 (20130101) |
Current International
Class: |
H01B
7/08 (20060101); H01B 7/00 (20060101); H01b
007/08 () |
Field of
Search: |
;174/113,117,117.11,117.1,112 (Inquired)/ |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Primary Examiner: Goldberg; E. A.
Parent Case Text
CROSS-REFERENCE TO RELATED APPLICATIONS
The present application is a continuation-in-part of copending and
now abandoned Ser. No. 695,595, filed Jan. 9, 1968 by Donald F.
Colglazier and assigned to the assignee of the present application.
Claims
I claim:
1. A cable for distributing electrical power, comprising:
a plurality of conductor assemblies extending in a longitudinal
direction, each said assembly including a thin flat conductive
strip extending in said longitudinal direction, a first pliable
insulative strip immediately and nonadheringly overlying said
conductive strip and having a plurality of edge regions extending
outwardly beyond the edges of said conductive strip in a direction
transverse to said longitudinal direction, and a second flat
pliable insulative strip immediately and nonadheringly underlying
said conductive strip and having a plurality of edge regions bonded
only to corresponding ones of said first-named edge regions so as
to allow said conductive strip to move in said longitudinal
direction relative to each of said insulative strips; and
restraining means holding said conductor assemblies one on top of
another so as to prevent substantial relative movement thereamong
in said transverse direction while permitting relative movement
thereamong in a direction perpendicular to said transverse
direction.
2. A cable according to claim 1 wherein said edge regions of said
second insulative strip of each assembly extend outwardly beyond
the edges of said conductive strip in said transverse direction,
said conductor and said strips of each assembly defining a pair of
interior, substantially triangular spaces enclosed by the edges of
said conductor and the bonded edge regions of said strips, each
said space having one relative small acute angle and two relatively
large angles.
3. A cable according to claim 2 wherein said restraining means
comprises a plurality of binding means disposed at spaced locations
along said longitudinal direction for preventing, at said
locations, substantial relative movement among said strips in a
direction perpendicular to both said longitudinal and said
transverse directions, and for permitting relative movement in said
perpendicular direction at other than said locations upon flexure
of said cable assembly.
4. A cable according to claim 2 wherein the aspect ratio of each of
said conductors is greater than about 25:1.
5. A cable according to claim 4 wherein the thickness of each of
said conductors is less than approximately 30 mils.
6. A cable according to claim 5 wherein the thickness of each of
said conductors is less than or equal to approximately 12 mils and
the width of at least one of said conductors is equal to or greater
than approximately 1000 mils.
7. A flat cable for distributing electrical power, comprising:
first and second lengthwise electrical conductors, each of said
conductors being of a substantially rectangular cross section and
having a width substantially exceeding a thickness thereof;
insulating means having a plurality of pliable insulating layers
immediately adjacent and slidably encasing each of said conductors
so as to permit lengthwise relative motion between said conductors
and said layers, each of said layers having a width exceeding the
width of said conductors associated therewith, at least two of said
layers encasing each conductor being edge-bonded to each other;
and
means supporting said first conductor on top of said second
conductor so as to restrain relative movement therebetween in the
direction of said conductor width while permitting relative
movement therebetween in a direction perpendicular to said
conductor width.
8. A cable according to claim 7 wherein said conductors are
slidably encased by said insulating layers, said conductors and
said layers defining a plurality of substantially triangular
spaces, each said space having one relatively small acute angle and
two relatively large angles.
9. A cable according to claim 8 wherein said insulating means
comprises a first pair of mutually edge-bonded insulating layers
encasing said first conductor and a second pair of mutually
edge-bonded insulating layers encasing said second conductor.
10. A cable according to claim 9 wherein said supporting means
encircles said conductors and both of said pairs of layers.
11. A cable according to claim 10 wherein said supporting means
comprises a lengthwise pliable insulative sheath loosely encasing
said layers and said conductors so as to permit lengthwise relative
movement between said layers and said sheath.
12. A cable according to claim 10 wherein said supporting means
comprises a plurality of spaced insulative binding means, each of
said binding means bonded to a plurality of said layers so as to
restrict lengthwise relative movement between said layers and said
binding means at the locations of said binding means, but so as to
permit relative movement between said locations.
13. A cable according to claim 9 further comprising:
a third lengthwise electrical conductor, said third conductor being
of a substantially rectangular cross section and having a width
substantially exceeding a thickness thereof;
a third pair of mutually edge-bonded insulative layers encasing
said third conductor; and
wherein said supporting means is constructed and arranged for
holding said third conductor beside said first conductor so as to
permit relative movement between said second and said third
conductors in a direction perpendicular to that of said conductor
widths.
14. A cable according to claim 13 further comprising:
a fourth lengthwise electrical conductor, said fourth conductor
being of a substantially rectangular cross section and having a
width substantially exceeding a thickness thereof;
a fourth pair of mutually edge-bonded insulative layers encasing
said third conductor; and
wherein said supporting means is constructed and arranged for
holding said fourth conductor beside said second conductor so as to
permit relative movement between said third and said fourth
conductors in a direction perpendicular to said conductor
widths.
15. A cable distributing electrical power, comprising:
a plurality of conductor assemblies extending in a longitudinal
direction, each said assembly including a thin flat conductive
strip extending in said longitudinal direction, a first pliable
insulative strip immediately and nonadheringly overlying said
conductive strip and having a plurality of edge regions extending
outwardly beyond the edges of said conductive strip in a direction
transverse to said longitudinal direction, and a second flat
pliable insulative strip immediately and nonadheringly underlying
said conductive strip and having a plurality of edge regions
extending outwardly beyond the edges of said conductive strip in
said transverse direction and bonded to corresponding ones of said
first-named edge regions so as to allow said conductive strip to
move in said longitudinal direction relative to each of said
insulative strips, said conductor and said strips of each assembly
defining a pair of interior, substantially triangular spaces
enclosed by the edges of said conductor and the bonded edge regions
of said strips, each said space having one relatively small acute
angle and two relatively large angles; and
restraining means comprising an insulative casing loosely disposed
about said assemblies for holding said conductor assemblies one on
top of another so as to permit relative movement thereamong in said
longitudinal direction while preventing substantial relative
movement thereamong in said transverse direction and in the
direction perpendicular to both said longitudinal and said
transverse directions.
Description
Background of the Invention
This invention relates to power cables and more particularly to
flat cables as commonly used in distributing power to electronic
systems.
The broad concept of a flat power cable is quite old; however to
date, all of these flat power cables have been susceptible to
damage when they were bent sharply. Bending of these cables would
cause conductors to pull through the insulation and short out to
each other or to a chassis around which the cables were bent. Also
if the cable successfully survived one flexure, reflexing the cable
to a new position would cause the cable to fail by shorting out or
by metal fatigue.
Some of the prior art cable designs are simply two flat conductors
mounted rigidly in the same insulating medium. Another flat cable
design is where multiple conductors are placed in the same flat
cable by having a flat conductor at the bottom of the cable and
multiple wire conductors placed immediately over the flat conductor
with all of these conductors being bonded to the same insulating
material to make up the cable. In either of these two types of
cables if a sharp flexure occurs, the metal conductor on the
outside of the flexure will have to stretch more than the other
inner conductor to make the bend. This additional stretch puts
additional tension in the outer conductor tending to pull it
through insulation towards the inner conductor.
If the prior art cables happen to survive the initial flexure
without shorting, their insulating material will usually be so
damaged that to straighten the cable and form another flexure will
almost certainly cause the cables to either short to the chassis
around which they are being bent or to short one to the other.
The problem is how to prevent a conductor in a flat cable from
being pulled through the insulation to another conductor in a flat
cable when the cable is bent or flexed sharply around a corner.
Cables in accordance with the invention find primary applications
in connection with electrical apparatus constructed from a number
of swingable, hingeable or demountable sections, wherein various
supply and bias voltages must be routed to some or all sections at
high current levels. More specifically, most large-scale computers
and similar devices have a stationary "main frame" containing
central power supplies, and a number of "gates" hinged therefrom so
as to swing outwardly for servicing and inspection. Each gate,
commonly 3 feet square or larger, contains many thousands of
individual circuits mounted on cards or boards attached to the
gate. It is therefore not unusual for even a single gate to require
supply currents on the order of 30 to 100 amperes or more. At the
same time such cables must be capable of sustaining repeated
flexures over bending diameters as small as one to four inches.
Prior attempts to meet these twin requirements have employed large,
round stranded wires, parallel smaller stranded wires arranged in a
flat configuration, and single flat conductors of the relatively
thick bus bar variety. None of these attempts, however, has
provided an adequate solution, and the lack of such a solution is
today a major impediment to the fabrication of easily serviceable
large-scale computers and other equipment.
It is therefore an object of this invention to produce a new flat
cable which has great flexibility and can be cycled through
multiple flexures without destroying its electrical integrity.
It is a further object of the invention to produce a flat power
cable which may be flexed around sharp corners and wherein the
outer conductor of the bend will not be pulled through the
insulation to short against the inner conductor of the bend.
SUMMARY OF THE INVENTION
In accordance with the invention the above objects are accomplished
by nonrigidly mounting the conductors in the flat cable so that the
conductors are free to slide or slip relative to each other. In one
embodiment of the invention, two flat conductors are insulated
separately with their own slidable insulating layers and the
resulting insulated conductors and then placed in a loose casing
with one insulated conductor laying on top of the other insulated
conductor. The insulated conductors are held loosely in position
over each other by an outer casing. Each insulated conductor can
slide relative to the other conductor and can also slide relative
to the outer casing. In an alternative embodiment, the separately
insulated conductors are fastened together by spaced tapes or bands
which, while preventing substantial relative movement between the
insulators at the taped locations, still permit each conductor to
slide within its own insulator, and further permit the conductors
to move toward or away from each other between the taped locations.
In a further embodiment, the individual flat conductors do not have
a layer of insulation bonded around them but instead are mounted in
an insulated cable or casing which is partitioned. The partition
lies horizontally across the width of the cable so that the
partition separates the two flat conductors. Each conductor is held
loosely in its partitioned section of the casing so that the
conductors can slide along the length of the casing relative to
each other and to the casing.
The great advantage of the invention is that it is very flexible
and even after many flexures the conductors will not pull through
the insulation or fail in fatigue. The conductors do not pull
through the insulation because they are slidable mounted in the
cable, and therefore the stretch or stress built up in a conductor
when the cable is bent around a corner is evenly distributed along
the length of the conductor since the entire conductor can stretch
to make the bend.
Stated another way, in the prior art where conductors were rigidly
tied to insulating material and to each other, the stresses built
up upon a conductor at a corner were restricted to a small length
of the conductor. Great force built up tending to pull the
conductor through the insulation. In the subject invention because
the conductor is slidably mounted relative to the other conductor
the stress is evenly distributed over a great length of conductor;
therefore, forces causing the conductor to be pulled through the
insulation are greatly reduced.
The provision of interior slip planes between each individual
conductor and its associated insulative covering is especially to
be noted. That is, each individual conductor may move relative to
its immediately adjacent insulating layers, even if the insulation
of one conductor is rigidly mounted to the insulation of another
conductor. This aspect of the invention not only leads to ease the
manufacture of such cables, but also enhances its stress-relieving
properties, since the stress is relieved at many more points, and
since the stress on the insulating layers is not permitted to add
to the stress on their associated conductors in any significant
manner. This method of stress relief has been completely
unappreciated by the prior-art flat cables of which applicant is
aware.
The foregoing and other objects, features and advantages of the
invention will be apparent from the following more particular
description of preferred embodiments of the invention as
illustrated in the accompanying drawings.
BRIEF DESCRIPTION OF DRAWINGS
FIG. 1 shows a flat power cable implemented by separately
insulating each flat conductor.
FIG. 2 shows a flat power cable implemented by placing two flat
conductors in separate partitions of an insulated casing.
FIGS. 3a and 3b show multiple conductor embodiments of the
invention utilizing conductors which are each insulated as in FIG.
1.
FIG. 4 illustrates, in a flexed condition, a multiple-conductor
cable employing tapes at spaced locations.
FIG. 5 is a perspective view, partly in cross section, of an
individual conductor assembly for use with the embodiments of FIGS.
1, 3a, 3b and 4.
DESCRIPTION
Referring now to FIG. 1, two flat conductors 10 and 12 are
surrounded by insulating material. Flat conductor 10 has bonded to
it a lower insulating layer 14 and upper insulating layer 16. A
flat insulated conductor can be formed by laying the flat conductor
10 on a layer of insulating material 14 and then overlaying the
assembly with another layer of insulating material 16 and heat
bonding the assembly. Conductor 12 is similarly insulated by
insulating layers 18 and 20. The entire assembly of conductors 10
and 12 with their insulating layers is contained in a flexible
casing 22. The function of the casing is to keep one insulated
conductor positioned over the other conductor. The casing could be
replaced by any mounting device which would keep the insulated
conductors properly positioned without rigidly holding them.
The significant fact of the construction of the cable and the
essence of this embodiment of the invention is that the insulated
conductor assembly 17 and the insulated conductor assembly 21 are
not rigidly mounted to each other or to the casing 22. In
particular, the casing 22 has sufficient inner dimensions to allow
for a slip plane 24 between the insulated conductor assemblies 17
and 21 and also for a slip plane 26 above the assembly 21 and some
space 28 below the assembly 17. As a result, the conductive
assemblies 17 and 21 are free to slide along the length of the
cable relative to each other and relative to the casing 22. As
previously pointed out by having the conductors slidably mounted,
the cable assembly may be flexed about sharp bends without the
conductors pulling through the insulating and shorting out.
FIG. 5 depicts, in greatly exaggerated size but approximately
correct relative proportions, a preferred form of conductor
assembly 17 of FIG. 1. Conductor assembly 21 (as well as
corresponding assemblies shown in FIGS. 3a and 3b) is preferably of
a similar construction.
The lengthwise or longitudinal conductor 10 is shown in FIG. 5 as a
metallic strip having a substantially rectangular cross section and
a width-to-thickness ratio, or aspect ratio, which is extremely
high in comparison to previous flat conductors used for
power-distribution purposes. A broad optimum for low-voltage
distribution systems, for instance, has been found to lie in the
neighborhood of a 1000 mil by 10 mil cross section, i.e., an aspect
ratio of 100:1. Minimum width is constrained to be at least about
500 mils for adequate current-handling capability; maximum width is
limited, primarily by the space available in associated electrical
equipment, to about 3000 mils. Current-handling capability and
mechanical strength dictate that the conductor thickness be above
approximately 5 mils. Maximum thickness is fairly sharply limited
by metal fatigue and flexibility to about 30 mils. More
specifically, it has been found that the present aluminum alloys
are entirely unsatisfactory at a 50-mil thickness, which is a very
small thickness in the power-distribution arts. Even a 20-mil
thickness dimension has been found to have perceptibly inferior
fatigue resistance as compared to the 10-mil optimum, Therefore, it
is preferable to increase current ratings by employing parallel,
individually insulated conductors of 10-mil to 20-mil dimensions
rather than by increasing the thickness much beyond 20 mils.
The above thicknesses are for commercially pure 1100 aluminum
according to ASTM Standard B211-68, which combines favorable
electrical and structural properties in relation to present-day
cost and availability. Although other metals or alloys may become
preferable in terms of the above trade-offs, it is considered
doubtful that thicknesses much more than 30 mils would be useful in
the present invention. Within the above limits, the aspect ratio of
the conductor should be greater than about 25:1 to ensure that the
conductor lies flat without twisting or turning sufficiently to
rupture the insulative covering or to change the orientation of the
cable conductors relative to each other. On the maximum side, the
aspect ratio should be restricted to less than approximately 300:1
in order to prevent curling of the conductor in a transverse
(width) direction within its insulative covering.
The insulative layers 14 and 16 are shown in FIG. 5 as thin, flat,
pliable strips having edge regions 41 extending outwardly in a
transverse direction beyond the edges 42 of conductive strip 10.
Since strips 14 and 16 are wider than conductor 10, regions 41 of
insulator 14 will directly underlie corresponding regions 41 of
insulator 16. Corresponding edge regions 41 may then be bonded to
each other in one of a number of simple, conventional and
inexpensive manufacturing techinques. If, for example, strips 14
and 16 are made of a thermoplastic such as polyethylene or Mylar (a
trademark of E. I. duPont de Nemours & Co. for a polyester
film), a sandwich comprising strips 10, 14 and 16 may be fed from
continuous rolls past heated rollers (not shown) for edge-bonding.
Strips 14 and 16 will adhere only to each other and not to the
conductive strip 10. The aforementioned high aspect ratio of
conductor 10 and the pliability of strips 14 and 16 then combine to
provide an insulative casing which establishes slip planes 43
between the surfaces of conductor 10 and the interior surfaces of
strips 14 and 16, so as to allow lengthwise or longitudinal
relative movement therebetween. The proximity of edge regions 41 to
the conductor edges 42, however, prevents any substantial
transverse or lateral movement of the encased conductor. The
apparently contradictory requirements of lengthwise mobility and
transverse restriction disappear almost entirely for the high
conductor aspect ratios noted hereinabove. FIG. 5 depicts, for
example, the loose fit between conductor and insulators in the
direction perpendicular to both the longitudinal and transverse
directions. This effect proceeds from the fact that the change in
length of strip 14 or 16 to achieve a given vertical separation
from conductor 10 becomes considerably less for a high aspect
ratio. In addition, this large width-to-thickness ratio greatly
decreases the angles between strips 14 and 16 adjacent the bonded
regions 41. Thus only a portion of edges 42 actually bear against
strips 14 and 16, and the relative stiffness of conductor 10 causes
it to act as a wedge attempting to separate the strips. Thus, the
above configuration produces a pair of triangular or wedge-shaped
interior spaces 50 enclosed by the conductor edges 42 and the
strips 14 and 16. Since the angles between strips 14 and 16 are
small, the angles between each strip and the edges 42 are
relatively large.
The edge-bonded regions 41 must, of course, be sufficiently wide to
secure an adequate bond and to prevent rupture thereof by the
conductor. But again the high aspect ratio of the conductor proves
to be an advantage. With no tensile stress being imposed in the
vertical direction by the wide, flat surfaces of conductor 10, the
bonds need withstand only the slight wedging forces relative motion
which is skewed from the lengthwise direction. Since the purpose of
lengthwise relative motion is only to relieve compressive and
tensile stresses in the assembly 17, the actual amount of the
motion is very small in relation to both the length and the width
of the assembly, and the maximum possible skew is therefore
insignificant. For the 1000-mil by 10-mil conductor described
above, e.g., the total width of each strip 14 and 16 may be
approximately 1125 mils (i.e., 11/8inches), yielding on edge bond
of 30 to 50 mils on each side. That is, the extra width required
for the bonded edge regions increases the total width of assembly
17 by only about 10 percent for a conductor aspect ratio of 100:1.
The thickness of each insulative strip 14 and 16 may conveniently
be approximately 5 mils in this instance, depending for the most
part on the magnitude of the voltages to be carried.
The assembly specifically detailed here was designed to carry 5
volts at a current of 60 amperes in free air, derated to 30 amperes
when used in a cable such as that shown in FIG. 1. A slightly
larger assembly, having a 1000-mil by 12-mil aluminum conductor and
1150-mil by 8.5-mil polyethylene insulating layers, was tested for
failure (conductor breakage or insulator rupture) by weighing one
end and bending it +90.degree.over mandrels having various sizes.
For mandrel diameters of 1/4, 1/2 and 11/4 inches, the average
numbers of complete bending cycles to cause failure were 735, 2000
and 5800, respectively, This assembly was designed for bending
diameters in the approximate range of 1 to 4 inches. Under
conditions of actual usage, therefore, it is virtually
indestructible.
Referring now to FIG. 2 an alternative embodiment of the invention
is shown. In this alternative embodiment the flat conductors 10 and
12 are mounted loosely in a conductive casing 30 which has an
insulating partition 32 to separate the conductors 10 and 12. The
conductors 10 and 12 are loosely mounted in the casing 30 having
ample space for each conductor 10 or 12 to slide along the length
of the cable in its associated partitioned section. That is, slip
planes are established between casing 30 and the conductors 10 and
12. The fact that the conductors 10 and 12 can slide relative to
each other and relative to the insulated casing 30 and partition 32
permits the cable assembly of the FIG. 2 to sustain very sharp
flexures around a bend without the conductors 10 and 12 pulling
through the insulation.
In FIGS. 3a and 3b, multiple conductor cables embodying the
invention are shown. Each of the metal conductive strips 40 is
surrounded by insulating layers or strips just as described in
connection with FIGS. 1 and 5. Each insulated conductor assembly is
thus a separate entity which is slidable relative to the other
insulated conductive assemblies.
FIG. 4 is a side elevation of a further embodiment according to the
present invention. This form of the cable 45 employs a number of
flat conductor assemblies 44, each of which is constructed in
accordance with the preceding description of representative
assembly 17. The assemblies appear in an edge-on aspect in order to
illustrate another type of stress-relieving relative motion
attainable under the invention. More particularly, the cable of
FIG. 1 permits substantial relative motion of conductors 10 and 12
in only one direction perpendicular to the conductor width, namely,
in the lengthwise or longitudinal direction of the conductors.
Cable 45, on the other hand, additionally allows substantial
relative movement in a vertical direction, i.e., in a direction
perpendicular both to the length and to the width of its
conductors.
Cable 45 comprises a stack of any number of flat conductor
assemblies 44 laid one on top of another; for clarity of
description, only four such assemblies are shown. Assemblies 44 are
restrained by discrete bands or bindings 46 encircling the
assemblies in the direction transverse to their length and disposed
at spaced locations 47 therealong. Bands 46 may conveniently be
strips of insulating adhesive tape adhering to at least the two
outer assemblies 44 and fastened upon themselves. For the 1000-mil
by 10-mil conductor size referred to above, the tapes may be, e.g.,
from about 1/2inch to one inch wide, and the spaced locations 47
may be, e.g., from about 3 inches to about 12 inches apart. The
only major requirements are that the locations 47 be sufficiently
close together to prevent substantial transverse (i.e.,
perpendicular to the plane of FIG. 4) relative motion between
assemblies 44, and that the tapes 46 be wide enough to avoid their
cutting into the cable 45 and to avoid the imposition of extremely
sharp bends in the cable when it is flexed near the locations 47.
In other respects, the width of tapes 46 and the spacing of
locations 47 are design choices to be determined from the
contemplated cable size and application.
Bindings 46 may alternatively be made of nonadhesive or even
noninsulating material. Where it is desired to affix the cable 45
to a mechanical support, e.g., the restraining function of bindings
46 may be accomplished by a clamp (not shown) or similar means.
Even when the bindings 46 adhere to some or all of the assemblies
44, the slip planes 43, described in connection with FIG. 5, still
allow longitudinal relative movement among the individual
conductors of the assemblies. Such movement may occur both at the
spaced locations 47 and at all locations 48 therebetween. In
addition, the assemblies 44 have another degree of freedom at the
locations 48, as shown by the arrows 49 in FIG. 4. That is, the
restraining means 46, being interrupted along the length of cable
45, permit the individual assemblies 44 and their respectively
encased conductors to move relative to each other in a direction
which is perpendicular both to their length and to their width.
The cable embodiment shown in FIG. 4 has three salient advantages,
for many applications, over the preceding variations having
continuous casings. First, the fabrication of the cable is rendered
easier and cheaper, especially in that it may be built up in situ
to exact specifications, without wastage, from a continuous roll
containing a single conductor assembly 44. Second, the provision
for relative movement in the direction 49 allows a large number of
assemblies 44 to be stacked into a single cable without the
introduction of undue stress. This is particularly true when the
cable is disposed within its associated equipment (not shown) such
that flexure will force the cable into the S-shape illustrated,
since this configuration places only insignificant longitudinal
stresses upon assemblies 44, so that there is no tendency for the
bindings 46 to be sheared or pulled out of shape. As stated
earlier, it is generally preferable to increase the current of
capacity of cables according to the invention by paralleling
conductor assemblies rather than by making the individual
assemblies larger in size. Therefore this second advantage
increases the current capability of the cable.
In the third place, the interrupted restraining means, and its
attendant increase in the number of assemblies in a single cable,
allows lateral connections or taps to the cable to be made in a
simple manner. In many power-distribution systems, it is necessary
that connections to individual conductors of a cable or bus bar be
brought out from the side. Conventional practice achieves this end
by the use of tabs, as illustrated, e.g., by U.S. Pat. No.
1,999,137. Such tabs, however, must either be initially built into
the conductors at specified locations or be mechanically affixed
thereto at installation. Either of these alternatives increases the
cost of the cable to a significant extent. Moreover, the only
practical connections to the tabs are by means of substantially
round wires, which decrease flexibility, which tend to break the
tabs by pulling and bending them, and which undesirably increase
the inductance of the system. The cable 45 of FIG. 4 overcomes
these disadvantages by allowing a large number of stress-relieved
parallel conductor assemblies such as 44. That is, cable 45 may
contain several assemblies 44 each carrying the same supply
voltage. A lateral tap may then be made at any location 48 merely
by folding one entire assembly out of the cable, in any desired
direction, and by connecting it directly to its individual load
(not shown). Such folding is made practical in the present
invention, of course, by the very high aspect ratio of the
individual conductors, as pointed out hereinabove.
It will be appreciated by one skilled in the art that other
electrical cable configurations can be designed using multiple flat
conductors of various configurations. Also in a two conductor cable
the conductors can be insulated from each other by giving only one
conductor an insulated coating. An outer casing would position the
conductors over each other and insulate the uncoated conductor from
conductive metal outside the cable.
While the invention has been particularly shown and described with
reference to preferred embodiments thereof, it will be understood
by those skilled in the art that various changes in form and
details may be made therein without departing from the spirit and
scope of the invention.
* * * * *