CA1094659A - Low resistance electrical connecting assembly - Google Patents

Abstract

LOW RESISTANCE ELECTRICAL CONNECTING ASSEMBLY
ABSTRACT OF THE DISCLOSURE
A low resistance electrical connecting assembly, each assembly including a plurality of operably arranged conductive elements, each element comprising a pair of relatively narrow, thin, outwardly convex, conducting contact surfaces supported on opposite sides of a latitudinal plane between them. The outwardly convex contact surfaces of each element are conductively associated to provide parallel current paths between source-side and load-side conductors in contact respectively with opposite ones of said conductive surfaces of each element. Such elements may be embodied in the form of a helical coil of conductive wire, each ring of the coil constituting one element. Another embodiment may be individual disks of conductive metal arranged in stacking relation-ship. Any number of other embodiments are possible which provide a plurality of elements as described, thin, outwardly convex conductive surfaces on opposite sides of a latitudinal plane, in closely adjacent side by side arrangement.

Description

;9 This invention relates t4 an assembly providing low resistance connections between electrical conductors and more particularly to an improved assembly for establishing a low resistance connection between conductors adapted to carry high current.
PRIOR ART
Connections between conductors carrying high currents such as 400 amps and above are subject to blow apart forces due to constricting current paths and opposing large magnetic fields.
Various attempts have been made to improve such connec-tions and reduce resistance as well as blow apart forces. One approach in avoiding the blow apart forces at the connection utilizes a jaw-like assembly with one end of the assembly secured to opposite sides of a bus bar and the ot~rend projec-ting forwardly to reeeive therebetween another bus bar. The jaw members are biased together by heavy springs to hold them tightly against the connected bus bars and to resist the blow apart forces. The contact surfaces of eaeh jaw member at the point of contaet with eaeh bus bar may be rounded to make the contact angle of current flow less acute which will tend to lessen blow apart forces. However, portions of such eonneeting jaws are still substantially parallel to both the source-side and load side bus bars and in relatively close proximity so magnetic fields of eurrent paths in such connecting jaws and parallel bus bars still create substantial blow apart foree.
The aforementîoned arrangement is also quite expensive, and imperfections in the engaged surfaces give rise to poor or high resistanee eontact and heating effects.
Arrangements to secure multiple current paths between associated conductors have used helical or coil springs. The 10'34~g turns of the springs provide a multiplicity oE engaged surfaces acting in parallel which are free to adjust themselves independ-ently to make good contact. This approach, as set out in British Patent 29,822, uses a hard drawn copper or phosphor bronze helical coil with the turns set at an angle of 60 to 80 from the axis of the helix to the points of engagement or contact.
This angle can provide high resistance to insertion or connecting forces, and phosphor bronze is inherently a high electrical resistance material with conductivity usually in the neighborhood of 18% of that of copper.
Copper, on the other hand, while providing low resist-ivity does not generally retain its resiliency in the high heat environments, such as that occurring in high current connections adapted to carry 400 amps or more. Temperatures in such en-vironments may be maintained at 100Cand may reach a maximum transient temperature of 150C for a 30 cps current.
It has, therefore, not been previously proposed to utilize a coil spring to establish connections between conductors adapted to carry currents of 400 amps or more.
SUMMARY OF THE INVENTION
This invention utilizes a coil spring for establishing low resistance connections between conductors adapted to carry currents of 400 amps or more. The problem of high insertion forces is avoided by substantially decreasing the angle between the turns of the spring and the axis of the helix or coil and by utilizing a joint compound and an angle of less than 50. This angle is preferabLy chosen as 45 and a coil-holding-trough is provided in one of the conductors, which ensures two points of engagement for the spring with the conductor.
According to one aspect of the present invention, there is provided, ~

ri9 an assembly for use .in establishing a low resistance electri.cal connection comprising, a pair of conductors each including aluminum and sized to carry either 400 amperes or more amperes of electrical current with each conductor having a planar surface and movable relative each other in a first direction parallel to each planar sur-face to place said surfaces in overlapping positions, the planar surface of one conductor of said pair of conductors having an elongate recess extending in a direction transverse to said first direction and having a bottom surface in said recess, said recess having longitudinal edges extending transverse to said first direction to define an opening communicating with the respective planar surface of said one conductor, a helical coil spring fcrmed of a copper cadmium alloy having a conductivity of at least 60% of that of pure copper adapted to remain resilient at a con-tinuous temperature of at least 100C located in said recess with each turn of said spring having an arcuate periphery formed about an axis of rotation located in the respective recess and having a diameter greater than the distance between said longitudinal edges and between said edges and said bottom surface whereby each turn of said spring engages said bottom surface at a respective tangent position to locate each turn of said spring in a plane having an angle of less than 50 to said axis of rotation, each periphery projecting from the respective recess through said openi:ng to a respective position spaced from the planar surface of said one conductor, means operative during th~e relative movement of said conductors in said first Idirection to space the planar ~ ~i 109/~S9 ., surfaces of said conductors apart by a distance less than the projecting periphery of each turn projects from the planar surface of said one conductor whereby each turn is engaged by the planar surface of the other conductor along the arcuate periphery and in a direction transverse to said axis of rotation in response to the relative movement between said conductors in said first direction to place said surfaces in said overlapping positions, the arcuate periphery of each turn lying in a plane having an angle of less than 50 to a respective planar surface of said one conductor for enabling a planar surface of the other conductor to facilely deflect each turn toward a respective planar surface of said one conductor and establish an electrical connection between said conductors in response to relative movement between said conductors in said first direction to place said surfaces in said overlapping .positions, and a joint compound on each planar surface and on the arcuate periphery of the turns of said spring.

" 1094659 1 I3RIEE' D~:SCRIP'LION OE' TIIE' D~`1Il`lGS
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2 Fig. 1 is a side eleva-tion view of one embodiment of this

3 invention in the form of a helical coil of conductive wire.

4 Fig. 2 is an exploded perspective view of a bus bar having conductive helical coils as shown in Fig. 1 restrainingly seated 6 ¦ transversely therein on opposite sides with portions projecting 7 outwardly from the contact surfaces of the bus bar for contact 8 with another conductor.
~ Fig. 3 is a side elevation view of the bus bar and an end view of the conductive helical coil shown in Fig. 2 with a second ¦
11 bus bar shown in connected contacting relationship therewith.
12 Fig. 4 is a perspective view of a modified form of the low 13 resistance connecting device in accordance with -this invention, 14 comprising axially aligned conductive discs in nested relation-ship to each other and restrainingly seated transversely in a 16 bus bar with a surface portion of each disc projecting outwardly 17 from the contact surface of the bus bar for contact with another 18 conductor.
19 Fig. 5 is a side elevation view of one ring element of the low resistance helical coil shown in Fig. 1 with the respective 21 adjacent ring elements on each side being broken away.
22 Fig. 6 is a side elevation view of the conductive discs 23 shown in Fig. 4.
24 Fig. 7 is an exploded perspective view of helical coils embodying this invention shown seated in a round socket con-26 ducting member of a plug-~in connection.
27 Fig. 8 is a section taken on line 8-8 of Fig. 3.
28 Fig~ 9 is a perspeclive view of a conductive contact arm of 29 a circuit breaker having a pivot end seated in a bus bar of the _~

~ ~a~ fi~9 1l `~` ~ l 1 circuit brea};er, and a helica:L coil oL- conductive wire in 2 accordance with this inven-tion seated in a recess of the bus bar.
3 Fig. 10 is an exploded perspective view of helical coils 4 embodying this invention shown seated in recesses formed around the circumference of a plug member of a plug-in type connec~ion.
6 Fig. 11 is a generally schematic isometric view of an 7 1 embodiment of the invention utilized in a high current applica-8 tion~
9 Fig. 12 is a sectional view taken through a spring recess, and 11 Fig. 13 is a longitudinal sectional view of a recess and 12 coil.
13 DESCRIPTION OF PR~FERRED ~MBODIMENT
14 A low resistance electrical connec-tin~ device in accordance with this invention may be embodied in the form of a helical coil 16 1 of conductive wire 2 such as copper cadmium. The wire should 17 be at least 60% IACS. It may be relatively thin and is preferablyj 18 silver plated for improved conductivi-ty. The rings 3 of -the coil j 19 ¦1 are arranged so close together in this invention, and the 20 ¦diameter of the coil is sufficiently small, whereby sufficient~
21 Isupport and rigidity is provided for the coil.
22 l! Each ring 3 of helical coil 1 comprises one conductive 23 element 4 in accordance with this invention. The invention is 24 described as being embodied in a helical coil for convenience of description, but the invention may be embodied in a wide variety 26 of resilient elements of suitable conductivi-ty. I
27 Each conductive element 4 includes a pair of outwardly con- ¦
28 ~vex surfaces 5 and 6, each supported on opposite sides of an 29 ~equatorial or latitudinal plane 7 between them as illustrated in .
~ 11 ~o~

Fig. 5. ~he plane between convex surfaces 5 and 6 may be at the equator dividing each into equal halves, but it need not be. It may be any latitudillal plane naving some part of an outwardly convex surface on each opposite side of the plane. The poles of such spnerical or convex surfaces 5 and 6 on opposite sides oL
such plane need not be axially aligned. They may be axially offset, or their axes may be randomly directed, but they are preferably conductively associated to provide parallel current paths between a source-side conductor 8 in contact with one set of said convex surfaces 5 and a load-side conductor 9 in contact with the opposite set of convex surfaces 6.
In the helical coil embodiment of this invention, the convex surfaces 5 and 6 are conductively associated to provide parallel current paths through the oppositely directed sides 4a and 4b each ring 3 of the helical coil~
As illustrated in Fig. 3, one side 4a of a ring of the coil 1 provides one conductive path between a point where convex surface 5 contacts source-side bus bar 8 an the points where convex surface 6 contacts load-side bus bar 9 at 6b.
The opposite side 4b of the coil ring provides an electri-cally parallel current path between the point where convex surface

5 contacts source-side bus bar 8 and the point 6d of convex surface 6 in contact with load-side bus bar 9.
Thus a current path from bus bar 8, convex surface 5, conductive path 4a, contact point 6a and bus bar 9 is electrically in parallel with a current path from bus bar 8, convex surface 5, conductive path 4b, contact point 6c and bus bar 9.
The conductive coils 1 may be seated in transv~rse recesses 10 and 11 formed in opposite sides of bus bar 9 opening to 109~6~9 1 respective surfaces 12 and 13. In this embocliment convex 2 surfaces 5 protruding outwardly from surfaces 12 and 13 respectiver 3 ly are proportionately smaller than their corresponding convex 4 surfaces 6 lying on the opposite side of respective planes through coils 1 which are co-planar with respective surfaces 12

6 and 13 of bus bar 9.

7 The coils 1 are preferably sea-ted in recesses 10 and 11

8 with their rings 3 inclined in side elevation with respect to

9 the surfaces 12 and 13 of bus bar 9. This arrangement tends to put the rings of the coil under a certain amount of tension or 11 tortional stress for better contact with the respective bus bars 12 8 and 9.
13 The width of the recesses 10 and 11 corresponds to the 14 circumferencial dimension of helical coils 1 to retain them snugly therein. The depth of the recesses is less than the 16 diameter of the coils 1 whereby the convex surfaces 5 of each of 17 the coil rings 3 protrude outwardly from the surfaces 12 and 13 18 of bus bar 9.
19 The cross-sectional configuration of recesses 10 and 11 may be polygonal as shown, rectangular, square, ovular or 21 circular, as long as they retain the helical coils snugly therein 22 with a convex surface 5 pro~ecting outwardly from ~he surfaces 23 f the bus bar.
24 Only one helical coil 1 is shown recessed in each opposite side of bus bar 9, in Fig. 2, but a plurality of recesses and 26 coils can be provided in each side of the bus bar throughout its 27 area which is in facing relation to a corresponding connected 28 bus bar.
29 ~ ~ modified embodiment of this invention ~s illustrated ln

10 ~ ,9 1 ~;`igs. ~ and 6. Ln this enlbodilllent eacll condllctive elernent 4' 2 consists of all indiviclual separate disk 3' is in nested engage-3 ment and capable of flexure in response to engagement by a planar 4 surface of another conductor and, preferably silver plated. The flexture may be provided by a bend in an equatorial plane to 6 enable resilient engagement witll the other conductor. The disks 7 may be in any of a variety of disk shapes, the only requirements 8 being that they have outwardly convex rim surfaces 5' and 6' 9 on opposite sides of a latitudinal plane between such surfaces, and the disks should be relatively thin in cross-section to

11 enable stacking a large number closely adjacent to each other

12 to provide many contact points and current paths for a given

13 area of conductors with which they are used.

14 The disks 3' may be concavo-convex with concave and convex side walls 14 and 15, respectively, for stacking in a nesting 16 relationship as illustrated in Fig. 6. Each disk may touch 17 adjacent disks or they may be slightly spaced apart.
18 Any number of other structural forms may be utilized to 19 embody this invention as long as they provide a multiplicity of outwardly convex conductive surfaces on opposite sides of a 21 latitudinal plane between them and with the oppositely disposed 22 convex surfaces conductively associa~ed to provide parallel 23 current paths.
24 The structural embodiment of this invention is preferably small in size relative to current carrying capacity, and easily 26 adapted for mounting across corresponding connecting surfaces of 27 respective source-side and load-side conductors. Fig. 7 illu-28 strates a helical coil embodiment of this invention for use in 29 a plug and socket type of connection. Two helical coils 1 are _g_ 1, _, iO~46~i9 1 shown seated in annular recesses 16 and 17 formed in the inner 2 conductive wall 18 of socket 19. Only one coil 1 in one recess 3 16 may be used, or a plurality of coils and recesses as shown.
4 The width of recesses 16 and 17 corresponds to the circumference of helical coils 1 to retain them snugly therein. The depth 6 of the recesses is less than the diameter of helical coils 1 whereby the convex surfaces S of each of said coil rings 3 8 protrudes from the surface of inner conductive 18 for contact ~ with surface 20 of plug conductor 21. Fig. 10 illustrates a plug and socket connection having the helical coils 1 mounted 11 on the plug conductor 21.
12 Since this invention includes a multiplicity of closely 13 adjacent individual elements each providing parallel current 14 paths, and minimal surface contact on the part of each element for highly efficient low resistance transfer of current from one 16 conductor or another, it ls particularly useful in electrically 17 connecting conductors having irregular surface shapes and contours .
18 Fig. 9 illustrates one application of this type, involving 19 a movable contact arm 22 of a circuit breaker having a pivot end seated in V-shaped recess 24 of conductor 25. A small 21 helical coil 1 in accordance with this invention, of preferably 22 silver plated wire, is seated in the vertex of V-shaped recess 24.1 23 Outwardly convex surfaces 5 project into the cavity of recess 24 24 for contact with the rounded surface edge 26 of the pivot end 23 f contact arm 22. The opposite outwardly convex surfaces 6 are 26 in contact with conductor 25. Prior to this invention, such 27 contact arm in this type of circuit breaker had only two contact 28 points at 27 and 28 along the respective side walls 29 and 30 of 29 the V-shaped recess 24. These were insuf-ficient when current ,~ ..... ~

increased beyond a given point to transfer the entire current between conductor 25 and contact arm 22, and to prevent the pivot end 23 from "popping" out of recess 24 due to blow apart forces. A shunting conductor 31 had to be provided for such increased current to prevent popping. The low resistance connecting device comprising helical coil 1 seated in recess 24 for contact between conductor 25 and contact arm 22 is able to transfer such increased current without the need of a shunting conductor 31.
The connecting elements and assembly in accordance with this invention may be embodied in a variety of different structures using a variety of different conductive materials, as long as the structure provides multiple parallel current paths between a source-side conductor and a load-side conductor.
Preferable specifications for the conductive material, whether it be a single element metal or an alloy, are tl) electrical conductivity with a resistivity no greater than 1.12 michroms-centimeter at 20 Centigrade, and (2) structural strength or stiffness equal to or greater than the modulus of rigidity of copper, or alternatively a modulus of rigidity equal to or greater than 15.0 X 106 pounds per square inch.
A preferred conductive material for use in this invention is copper which may be silver plated for better conductivity.
Illustrative examples of other conductive materials that would be suitable are alloys of beryllium copper, phosphor bron~e and aluminum. Illustrative examples of other plating materials which would be suitable for use with this invention include tin plating and cadmium plating.
In E'ig. 11 a portion of a plug-in or switchboard unit 50 is schematically illustrated for extending a connection from a lin~

10'~ i9 1¦ terminal 52 to a load termirlal 54. The line terminal 52 extends 21 from a bus bar, for example, and -typically may carry 400, 800 or 3 1200 amperes and is connected to a conductor or stab 56 pro-4 jecting from the unit 50 in response to movement of the unit 50 toward the terminal 52. The stab 56 in turn extends a connection ¦
6 from the terminal 52 through a circuit breaker or switch generally 7 indicated at 58 of the plug-in unit to a conductor or jaw 60 8 adapted to receive the stab or load terminal 54 for extending 9 power to a load.
The line terminal 52 comprises a jaw or a pair of spaced 11 legs having spaced planar surfaces adapted to receive the spaced 12 planar surfaces of stab 56 therebetween. Each surface of stab 13 56 contains a plurality of elongated channels, troughs or 14 ¦recesses 62 extending transverse at an outer angle to the direction of movement between the stab 56 and terminal 52. Each 16 recess retains a respective coil spring 64 for engaging the 17 surfaces of terminal 52. A crimp 65 in the recess edge adjacent 18 each end of a respective coil spring limits longitudinal movement j 19 of the spring.
The load terminal 54 comprises a parallelepiped stab whose 21 forward or engagement end is bevelled for sequentially engaging 22 Ithe coils or turns 66 of a coil spring 64 carried in a respective 23 lone of a plurality of recesses 68 of jaw 60. Contact between 24 Istab 54 and coils 66 is therefore gradual and limits the total force necessary for engagement in a manner similar to tha-t 26 between springs 64 carried by stab 56 and terminal 52.
27 Each trolgh as seen in Fig. 12 is polygonally shaped having 28 sides a-g with relatively short sides b and f and the recess 29 extends substantially 270 about each spring to define an opening ¦
ll ~ I

.-..

1 communicat~llg wi-th the adjacent planar surface. The opening 2 permits the spring to extend or project above the respective 3 planar surface for substantially .03". ~s can be seen in Fig. 13,¦
4 the conductive coils are positioned in the trough so that the coil turns are at an angle less than 50 from the axis of the 6 coil or adjacent planar surfaces and preferably 45 as shown.
7 This angle is of critical importance as it reduces the force 8 necessary to secure engagement between the coils and the mating ~ surfaces, while retaining the necessary resilient engagement between the opposing or mating conductors to ensure uniform 11 multiple current paths.
12 Fig. 12 shows the two points of contact or tangency between 13 each turn of conductive coil 64 and the surface of trough 62, 14 as occurs during engagement with a matiny surface. One point f contact along side c and the other contact point along side e 16 each at substantially 135 to a normal N between a mating surface ¦
17 f terminals 52 or 54 and the respective turn to permit facile 18 deformation of the coil in the directions of sides b, d and f.
19 When the terminals 52 or 54 are disengaged from the respective spring the turns expand so that they are also tangent to the 21 surfaces a and g terminate substantially at a respective point 22 of tangency with the spring to permit the spring to project from 23 the recess 62, however in fabrication the surfaces a and g 24 initially extend beyond the point of tangency as shown by dotted lines D and are machined off, since the conductors or terminals 26 are yenerally formed from extruded aluminum and cannot be 27 accurately extruded to the desired dimension.
28 The coils have an outer diameter of substantially .250"
29 and are for ~d from cadmi~n copper alloy 162 wire of .02" diameter l ll _ ~
.... _ ~

This wire has a resistance of less than 50 microhms per ineh, with 25 turns per inch, and peak currents of 20 kiloamps per inch can be safely carried. A silver plate of .00025" minimum is applied to the wire and a similar plate is applied to the planar terminal surfaces. The cadmium copper alloy has a conductivity of substantially 82% of IACS and should not be less than 60% IACS for use in the described arrange~ent. This spring arrangement retains its resiliency or elasticity at maximum transient temperatures of 150 C for 30 cps or at continuous temperatures of 100C.
In addition a joint compound such as Cu-AlAid or No-Oxid, or petroleum base compounds are provided on the springs and/or adjacent surfaces to reduce friction and to protect against chemical attack such as sulfides on the silver plate, or oxidation and to enhance thermal eonduetivity.
To extend a eonnection from the line terminal 52 to the load terminal 54, the plug-on unit 50 is moved relative the terminals to engage the stab 56 between the spaced planar surfaces of terminal 52 and the stab 54 is moved between the spaced planar surfaces of terminals 60. As the planar surfaces move into overlapping positions, the terminal 52 sequentially engages the turns of coil 64 since the axis of the eoils are positioned at an acute angle to the direction of movement.
This in eonjunetion with the angle of 45 between the plane of the eoil turns and their axis or the planar surface and the joint eompound substantially reduees the foree required for engagement an facilitates re!petitive engagement with minimum danger of damage. A similar result is achieved by the beveled end of stab 54 engaging the coil turns in sequence.

109~fi59 l As the planar surfaces of terminals 52 and 54 engage the 2 projecting springs the spring turns are compressed into the 3 respective recesses and the angle to the axis tends to be reduced 4 below 45 as the turns both slide relative each other and deform 51 into the recess. The spring turns move ffrom engagement with 6 surfaces a and g and are held tightly engaged under spring 7 pressure between surfaces c and e and the planar surface of the 8 mating terminal. The springs in this arrangement provide sub-9 stantially equal engage~ent pressure at all points to ensure multiple paths for current flow irrespective of tolerance ll problems or minor differences in the spacing of the planar 12 surfaces.
13 The foregoiny is a description of the preferred embodiments 14 and the inventive concepts are believed set forth in the 16 accompanying claims. ¦' l78 23 .

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Claims (8)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. An assembly for use in establishing a low resistance electrical connection comprising;
a pair of conductors each including aluminum and sized to carry either 400 amperes or more amperes of electrical current with each conductor having a planar surface and movable relative each other in a first direction parallel to each planar surface to place said surfaces in overlapping positions, the planar surface of one conductor of said pair of conductors having an elongate recess extending in a direction transverse to said first direction and having a bottom surface in said recess, said recess having longitudinal edges extending transverse to said first direction to define an opening communicating with the respective planar surface of said one conductor, a helical coil spring formed of a copper cadmium alloy having a conductivity of at least 60% of that of pure copper adapted to remain resilient at a continuous temperature of at least 100°C
located in said recess with each turn of said spring having an arcuate periphery formed about an axis of rotation located in the respective recess and having a diameter greater than the distance between said longitudinal edges and between said edges and said bottom surface whereby each turn of said spring engages said bottom surface at a respective tangent position to locate each turn of said spring in a plane having an angle of less than 50° to said axis of rotation, each periphery projecting from the respective recess through said opening to a respective position spaced from the planar surface of said one conductor, means operative during the relative movement of said conductors in said first direction to space the planar surfaces of said conductors apart by a distance less than the projecting periphery of each turn projects from the planar surface of said one conductor whereby each turn is engaged by the planar surface of the other conductor along the arcuate periphery and in a direction transverse to said axis of rotation in response to the relative movement between said conductors in said first direction to place said surfaces in said overlapping positions, the arcuate periphery of each turn lying in a plane having an angle of less than 50° to a respective planar surface of said one conductor for enabling a planar surface of the other conductor to facilely deflect each turn toward a respective planar surface of said one conductor and establish an electrical connection between said conductors in response to relative movement between said conductors in said first direction to place said surfaces in said overlapping positions, and a joint compound on each planar surface and on the arcuate periphery of the turns of said spring.

2. A low resistance electrical connecting assembly as set forth in Claim 1 wherein said spring and said planar surfaces are each silver plated.

3. An assembly as claimed in Claim 1 wherein the edges of said elongate recess are crimped adjacent opposite ends of said spring to retain the turns of said spring in a predetermined relationship.

4. An assembly as claimed in Claim 1 wherein said recess extends at least 180° about said spring and is tangent to said spring at least two spaced positions.

5. The assembly claimed in Claim 4 in which said spaced positions are substantially 135° to a line normal to said spring and the engaged planar surface.

6. The assembly claimed in Claim 5 in which a plurality of recesses are provided each having an elongate axis extending at an acute angle to the said first direction.

7. The assembly as claimed in Claim 5 in which one end of said other conductor is bevelled to engage each turn of a respective spring in sequence.

8. The assembly as claimed in Claim 1 wherein each turn of each spring projects substantially .03" from the respective recess and each spring has an outer diameter of substantially .25" and is formed from wire of substantially .02".