US3824555A - Electrical conductor terminal assembly - Google Patents

Abstract

An assembly for making an electrical connection between a flat terminal strap and an aluminum conductor, comprising a U-shaped saddle member including a pair of leg sections adapted to straddle the strap, a bolt captured in a free-turning relation in the bridging section between the leg sections and threadedly engaging the strap, a resilient washer positioned between the bottom of the head of the bolt and the bridging section of the saddle member, and wherein the saddle member is aluminum and the leg sections of the saddle member are straight, parallel and of arcuate cross section.

Description

Klein et al.

[11] 3,824,555 [451 July 16, 1974 ELECTRICAL CONDUCTOR TERMINAL ASSEMBLY Inventors: Keith William Klein, Simsbury;

Joseph Michael Palmieri, Southington, both of Conn.

General Electric Company, New York, NY.

Filedz Apr. 2, 1973 Appl. No.: 347,127

Assignee:

U.S. Cl. 339/246, 339/269 Int. Cl HOlr 7/24 Field of Search 339/244, 246, 269, 271;

24/125 R, 135 B, 81 CC References Cited FOREIGN PATENTS OR APPLICATIONS 632,048 11/1949 Great Britain 339/246 Primary ExaminerJoseph H. McGlynn Attorney, Agent, or FirmRobert A. Cahill; Philip L. Schlamp; Frank L. Neuhauser [57] ABSTRACT An assembly for making an electrical connection between a flat terminal strap and an aluminum conductor, comprising a U-shaped saddle member including a pair of leg sections adapted to straddle the strap, a bolt captured in a free-turning relation in the bridging section between the leg sections and threadedly engaging the strap, a resilient washer positioned between the bottom of the head of the bolt and the bridging section of the saddle member, and wherein the saddle member is aluminum andthe leg sections of the saddle member are straight, parallel and of arcuate cross sectron.

2 Claims, 6 Drawing Figures ELECTRICAL CONDUCTOR TERMINAL ASSEMBLY BACKGROUND OF THE INVENTION Heretofore difficulties have been generally experienced in making tight electrically dependable connections between wires and the flat terminal straps commonly used in various electrical devices such, for example, as molded case circuit breakers, switches, relays and the like. More specifically, in such devices electrical connections are generally made between the terminal straps and the wires by clamping devices of various kinds serving to hold the wires and terminal straps in a tight electrical contact. One example of such connectors is shown in U.S. Pat. No. 3,191,140Coldren. However, these devices place the wire and cooperating strap and clamping elements in compression, and when the wire and any of such cooperating elements are formed of aluminum or other relatively soft materials there is a tendency for them to cold flow or deform under the compressive stresses therein. This deformation, in turn, adversely affects the mechanical and electrical connections between the elements. A connector described as effective for overcoming this problem in the connection of two aluminum wires is shown in U.S. Pat. No. 2,77l,59lVordtriede.

ln connectors of the presently considered type the wire tends to assume a flattened cross-sectional configuration between the flat terminal strap and the flat inner surface of the saddle member and thus become loosened mechanically and less intimately connected electrically. Similarly, the terminal strap is often formed of aluminum or surface-coated with aluminum or other relatively soft metal for desired heat transfer and dissipation purposes and to provide for improved electrical contact with the aluminum wire. In this case the compressive effect of the wire on the surface of the strap can cause the underlying aluminum or other soft metal of the strap surface to flow outwardly from under the wire and thus also cause loosening of the wire and undesired effects in the electrical contact therebetween. Due to the desirable heat transfer and dissipation properties of aluminum, the clamping elements are advantageously wholly formed of aluminum. However, here too the compressive stresses induced in the clamp legs can cause a tendency for them to bow and thus relieve somewhat the contacting pressure between the wire and terminal strap.

In addition to the above-reference advantages of forming the clamping elements of aluminum, the provision of a connection assembly wherein the terminal strap, wire conductor and clamping element are all formed of aluminum is desirable because of resultant cost and weight advantages as well as protection against corrosion due to galvanic action which is generally encountered when parts formed of dissimilar metals are used. Thus, it is highly desirable to provide an essentially all-aluminum assembly which is also effective and dependable in maintaining satisfactory electrical contact of parts regardless of possible deformation in the aluminum pars when maintained under compressive stresses.

Furthermore, in devices embodying electrical connector assemblies of the above-discussed type space is often at a premium. For example. in certain molded case circuit breakers the lateral dimensions of the terminal straps must, owing to available space considerations, be minimized as must be the corresponding dimensions of cooperating wire clamping elements. Yet it is desirable that the space in the assembly for receiving the wire to be connected be maximized to enable greater choice inthe gauge of wire to be employed.

Still further, it is desirable that the parts of electrical connector assemblies be adapted for cooperating in a manner which facilitates the making of a dependable initial electrical contact between the parts and for minimizing any undesired relative motion between such parts which could adversely affect such contact during normal operating lift of an assembly.

OBJECT OF THE INVENTION A general object of the present invention is to provide an electrical connector adapted for assuring reliable electrical connections between flat terminal straps of electrical devices and wire conductors formed of aluminum and other relatively soft metals which have a tendency to deform under compressive stresses induced by electrical clamping elements and thereby adversely affect the electrical integrity of the connections. I l

Another object of the present invention is to provide a dependable electrical connector which is particularly suited for use where connection space is at a premium but which isalso effective for maximizing the gauge of wire conductor usable therein.

Still another object of the present invention is to provide an electrical connector which, in cooperation with aluminum terminal straps and aluminum wire conductors, affords an essentially wholly aluminum assembly in order to gain desired cost, weight, electrical and thermal conductivity and corrosion resistance advantages while also affording the electrical contact dependability desired.

SUMMARY OF THE INVENTION In accordance with one embodiment of the invention, an assembly is provided for making connection to a flat terminal strap which can comprise part of an electrical'device such as a molded case circuit breaker, a relay, a switch or'any other similar structure. The strap is provided near its end with a tapped aperture to receive a bolt or screw adapted for drawing a conductive clamping element down onto the strap in a manner effective for securing a wire conductor in electrical contact with the strap.

The strap is rectangular in cross section to provide a flat upper surface to cooperate with the wire, and parallel vertical sides to cooperate effectively with the clamping element. More specifically, the clamping element is a conductive saddle member formed with a pair of pendent leg sections and a bridging section joining the leg sections. The bridging section is centrally apertured and has a flat extensive bearing surface surrounding the aperture therein. Suitably staked in the bridging aperture so as to be retained therein in relatively loose free-turning relation is a drawbolt or screw which has a threaded shank extending downward between the leg sections of the saddle member for being threaded into the tapped aperture of the terminal strap. When a wire conductor is disposed between the saddle member and strap and the drawbolt is tightened, the wire is compressed between the flat lower side of the bridging section of the saddle member and the flat upper surface of the strap for effecting a desired electrical contact between the wire and strap.

The leg sections are arcuate in cross section to provide maximum radial space between thebolt shank and the. leg sections and to rigidize the legs in parallel spaced relationAlso, the opposed edges of the leg sections are parallel and predeterminedlyspaced apart to provide a close-fitting sliding relation with respect to the terminal strap positioned therebetween.

The drawbolt head extends broadly over the bearing surface on the bridging section of the saddle member and includes a flat bearingsurface on its underside facing the bearing surface on the bridging section. Loosely mounted on the bolt and positioned between the bearing surfaces on the bolt and bridging section is a concavo-convex spring washer. The convex surface of the spring washer engages the flat bearing surface under the bolt head and the rim extends broadly outwardly and engages and bearing surface'on the bridging section of the saddle member.

DESCRIPTION OF THE DRAWING In the drawing, I FIG. 1 is a perspective view of an electrical connection assembly embodying a preferred form of the invention;

FIG. 2 is an elevational view of the assembly of FIG. I with the terminal strap and wire conductor illustrated in'cross section;

FIG. 3 is a bottom plan view of the assembly shown in FIG. 2;

FIG. 4 is an enlarged fragmentary sectional view il- DETAILED DESCRIPTION OF APREFERRED EMBODIMENT The inventin is shown in FIG. 1-3 effecting an electrical connection between a flat terminal strap 10 and a wire conductor 11. The strap 10 is elongated, rectangular in cross section, and typical of the terminal straps or lugs which are used as external terminals in many electrical devices such as molded case circuit breakers, relays, switches and the like. The wire conductor 11 may be a single conductor, as shown, or a multi-strand conductor and, as will be brought out in detail hereinafter, the present invention is most advantageously employed when the wire is formed of aluminum or other relatively soft metals including copper.-

Cooperating with the strap 10 to secure the wire 11 in firm electrical contact therewith is a connector 12 comprising a generally U-shaped floating clamp or saddle member 13. The saddle member 13 is formed to include a pair of pendent leg sections 14 and a bridging section 15 joining the leg sections. The leg sections 14 constitute opposed spaced sections of a cylindrical section depending from the bridging section and, as best seen in F lG..3, are arcuate in cross section throughout the lengths thereof. Additionally, the opposed inner edges 16 of the leg sections are predeterminedly spaced for receiving the terminal strap 10 therebetween in closely fitting sliding and guiding relation, the purpose for which will be brought out in detail hereinafter.

The bridging section 15 is providedwith a centrally located aperture 17 in which, as best seen in FIGS. 3 and 4, there is mounted adrawbolt or screw 18. The bolt 18 includes a head 19, which is preferably slotted, as shown, for screw driver tightening but which can, if desired, be provided with lands for wrench tightening, a threaded shank portion 20 and an intermediate reduced section 21. The reduced section 21 is located in the bridging section aperture 17 and is smaller in diameter than the aperture. Also, the region of the bridging section constituting the underside edgeof the aperture 17 is staked or inwardly displaced to a diameter less than the diameter of the threaded portion of the shank. This arrangement is effective for retaining the bolt 18 in a relatively loose, free-turning relation in the bridging section.

The threaded shank 20 of the bolt 18 is adapted for threadedly engaging the terminal strap 10 in the manner illustrated and, when tightened, is effective for drawing the terminal strap 10 toward the bridging section of the saddle member and into a secure contacting relation with the wire conductor 11 positioned therebetween. r

The relative dimensioning of the strap 10 and the spacing to provide a close fit and the straight, parallel vertical edges 16 on the leg sections of the saddle member all cooperate effectively to provide for vertical guided movement of the strap into, engagement with the wire and to minimize any other relative movement of the parts during the tightening of the bolt or during subsequent operating life, which latter movement, if permitted, could result in adversely affecting the wire holding effect of the arrangement and the electrical contact between the wire and strap.

Additionally, there is provided between the head 19 of the bolt and the bridging section 15 of the saddle member a concavo-convex or dished spring washer 22. More specifically, the upper surface and the bolt head is enlarged and of a diameter greater than the width of the bridging section. Also,' the underside of the bolt head is flat and this together'with the large diameter of the head effectively adapts it for presenting a bearing surface opposing and extending substantially over the bearing surface surrounding the aperture in the bridging section. Disposed between these opposed bearing surfaces and mounted loosely on the reduced section of the bolt shank is the above-referenced spring washer 22 which preferably also has an outer diameter greater than the width of the bridging section and the outer diameter of the bolt head. The spring washer 22 is preferably of the so-called Belleville type"- and its purpose and the manner in which it effectively cooperates with the other elements in the described assembly will now be described in detail.

The disclosed arrangement, as indicatedabove, is most advantageously employed where the wire conductor 10 is formed of aluminum or another relatively soft metal and where such conductors have a tendency to cold flow or deform under pressure. More specifically, when aluminum and other soft metal conductors are clamped or held in compression in a clamping'conne'ctor of the described type, the wire section held firmly under Compressive stress between the terminal strap and saddle member tends to cold flow outwardly or flatten in cross section. Unless appropriate compensating means is provided, this flattening of the wire can cause it to become loosened in the clamp or to degrade the electrical contact between the wire and terminal, Similarly, it is often desirable to have the terminal strap either wholly formed of aluminum and coated with tin, or formed of another metal and surface coated with tin or aluminum, and to form the saddle member of aluminum also, all for the purpose of enhanced thermal and electrical conductivity as well as weight and cost advantages and avoidance of corrosion due to galvanic action. Using aluminum for the saddle member, strap and wire also affords greater uniformity of the coefficients of expansion of the cooperating elements and thus minimizes chances of undesirable loosening due to differences in thermal expansion and contraction of parts during operating life.

However, when a terminal strap or the saddle member are formed of, or-coated with a soft metal, they too are subject to a certain amount of cold flow or deformation under compressive stresses induced by the tightening of the drawbolt. This can occur at the surfaces thereof engaged by the wire and can contribute to the looseningof the wire or can adversely affect the electrical contact between the wire and terminal. The just-described adverse effects are avoided or greatly minimized by the arrangement including the large bolt head, the extensive bearing surfaces on the bolt head and bridging section and the large diameter Belleville washer therebetween. More specifically, the large bolt head and large underside bearing surface enable substantial area contact with the spring washer and resultant substantial pressure to be brought to bear and to be maintained on an extensive area of the upper surface of the spring washer. This pressure is substantially greater than that which can be afforded, for example, by the circular line of contact arrangement shown in U.S. Pat. No. 2,771,59l-Vrdtrided, and thus it serves to readily compress the spring washer; and the spring washer, owing to its substantial diameter and the relatively large bearing surface on the bridging section of the saddle member, transmits and maintains considerable spring pressure on the saddle member for urging it into firm contact with the wire conductor and thereby maintaining the wire conductor in firm contacting relation with the strap. Thus, the spring follows up or compensates for any deformation of the wire or other soft metal elements which could otherwise affect the electrical contact therebetween.

In the described connector, the large bolt head and the broad extension of the Belleville spring over the large bearing surface on the bridging section of the saddle member together with the loose fit of the saddle member and spring on the bolt shank, serve to cooperate in uniformly drawing the strap up into the saddle member and in enabling an assembler to quickly and securely fasten a wire conductor in place and in contact with the terminal strap. Also, the abovedescribed predetermined relative dimensioning of the strap and the close fit of the straight parallel inner edges of the leg sections astraddle the strap causes the strap to move and be guided substantially straight upwardly between the leg sections and into clamping engagement with a minimum of any wobbling" movement of the saddle member during assembly. This serves to provide more uniform dependable clamping action of the assembly.

The present invention is also effective for maximizing the diameter of wire that may be used with a terminal strap of a given width. This is particularly advantageous where space is at a premium, such as in the application illustrated in FIG. 6, wherein the case 23 of the device which may, for example, be a molded case circuit breaker, has a relatively small recess 24 in which the external portion of the terminal strap 10 is located and the strap must necessarily be limited to a particular width. As seen in FIG. 3, when the wire diameter is less than the dimension from the bolt shank to the side edges of the leg sections, the arcuate cross-sectional configuration of the legs serves only one function, namely, to rigidize the leg sections. This better adapts a thinner gauge and relatively soft metal, such as aluminium stock, for use in fabricating the saddle member.

However, the arcuate cross-sectional configuration of the legs serves a very effective second function when it is desired to use a larger diameter wire. More specifically, and as best seen in FIG. 5, the arcuate cross section of the legs provides spaces between the bolt shank and inner surfaces of the legs which are substantially greater in radial length than the available spaces would be if the legs had flat inner surfaces of the type shown, for example, in. U.S. Pat. No. 3,191,l40-Coldren. Thus, a relatively large diameter conductor 25 can be bent and inserted into the space between the bolt shank and leg section. A portion of the wire may extend slightly over the outer edge of the terminal strap but the wire would be securely clamped between the strap and saddle member and adequate electrical contact would be afforded between the wire and substantial engaging surfaces of the terminal strap.

Various modifications may be made in the connector assembly illustrated without departing from the invention, and other modifications will occur to persons familiar with and skilled in the art when exposed to the present invention. It is therefore intended, by the appended claims, to cover all such modifications as fully within the true spirit and scope of the invention.

What is claimed as new and desired to be secured by Letters Patent of the United States is:

1. A terminal connector for making an electrical connection to an aluminum wire conductor, said connector comprising:

a. a flat terminal strap of rectangular cross section and having, 1. at least a contact surface portion of relatively soft metal and, 2. a threaded aperture extending through said contact surface portion; b. an aluminum saddle member having,

1. a pair of pendent parallel leg sections for straddling said strap, and 2. a bridging section joining said leg sections and having a centrally located aperture and a flat bearing surface surrounding said aperture; c. a drawbolt retained in free-turning relation in said aperture in said saddle member and having, 1. a head with a substantial flat bearing surface on the underside thereof and extending broadly over said bridging section of said saddle member, and

2-. a threaded shank extending between the legs of said saddle member for threadedly engaging said aperture in said strap and effective when said bolt is tightened for drawing said contact surface of said strap into conductive engagement with said aluminum wire conductor disposed between said strap and saddle member; and d. a spring washer mounted on said bolt between said bearing surfaces on said saddle member and said bolt head, said washer extending outwardly of said bolt head and broadly over said bridge of said saddle member, and effective when compressed by the tightening of said bolt to provide a continuous compressive force on said aluminum conductor to maintain a satisfactory electrical contact with said strap regardless of any tendency of said conductor or connector parts to deform under pressure.

2. An assembly for making a reliable electrical connection to an aluminum wire comprising:

a. a flat terminal strap of rectangular cross section and having,

l. at least a contact surface portion of relatively soft metal and,

2. a threaded aperture extending through said contact surface portion;

b. an aluminum saddle member having,

1. a pair of legs constituting opposed sections of a cylinder and having straight parallel inner edges straddling and in closely fitting sliding relationship with said strap, and

2. a bridging section joining said legs and having a centrally located aperture, a flat bearing surface on the outer surface of said section surrounding said aperture and being extensive relative to the surface of said bridging section;

c. a drawbolt retained in free-turning relation in said aperture in said saddle member and having,

1. a head with a flat bearing surface on the underside thereof which is extensive in relation to the surface of said bridging section of said saddle member, and

2. a threaded shank extending between the legs of said saddle member and threaded in said aperture in said strap, and effective when said bolt is tightened for drawing said contact surface on said strap into conductive engagement with an aluminum wire positioned between said strap and saddle member; and

d. a concavo-convex spring washer mounted on said bolt between said bearing surfaces of said saddle member and said bolt head and effective when compressed by the tightening of said bolt to provide a continuous compressive force on said aluminum wire through said strap to compensate for any deformation of the aluminum under pressure and thereby maintain a satisfactory electrical connection between said wire and said contact surface of said strap.

Claims (8)

1. A terminal connector for making an electrical connection to an aluminum wire conductor, said connector comprising: a. a flat terminal strap of rectangular cross section and having, 1. at least a contact surface portion of relatively soft metal and, 2. a threaded aperture extending through said contact surface portion; b. an aluminum saddle member having, 1. a pair of pendent parallel leg sections for straddling said strap, and 2. a bridging section joining said leg sections and having a centrally located aperture and a flat bearing surface surrounding said aperture; c. a drawbolt retained in free-turning relation in said aperture in said saddle member and having, 1. a head with a substantial flat bearing surface on the underside thereof and extending broadly over said bridging section of said saddle member, and 2. a threaded shank extending between the legs of said saddle member for threadedly engaging said aperture in said strap and effective when said bolt is tightened for drawing said contact surface of said strap into conductive engagement with said aluminum wire conductor disposed between said strap and saddle member; and d. a spring washer mounted on said bolt between said bearing surfaces on said saddle member and said bolt head, said washer extending outwardly of said bolt head and broadly over said bridge of said saddle member, and effective when compressed by the tightening of said bolt to provide a continuous compressive force on said aluminum conductor to maintain a satisfactory electrical contact with said strap regardless of any tendency of said conductor or connector parts to deform under pressure.

2. a threaded shank extending between the legs of said saddle member and threaded in said aperture in said strap, and effective when said bolt is tightened for drawing said contact surface on said strap into conductive engagement with an aluminum wire positioned between said strap and saddle member; and d. a concavo-convex spring washer mounted on said bolt between said bearing surfaces of said saddle member and said bolt head and effective when compressed by the tightening of said bolt to provide a continuous compressive force on said aluminum wire through said strap to compensate for any deformation of the aluminum under pressure and thereby maintain a satisfactory electrical connection between said wire and said contact surface of said strap.

2. a bridging section joining said legs and having a centrally located aperture, a flat bearing surface on the outer surface of said section surrounding said aperture and being extensive relative to the surface of said bridging section; c. a drawbolt retained in free-turning relation in said aperture in said saddle member and having,

2. a threaded aperture extending through said contact surface portion; b. an aluminum saddle member having,

2. An assembly for making a reliable electrical connection to an aluminum wire comprising: a. a flat terminal strap of rectangular cross section and having,

2. a threaded shank extending between the legs of said saddle member for threadedly engaging said aperture in said strap and effective when said bolt is tightened for drawing said contact surface of said strap into conductive engagement with said aluminum wire conductor disposed between said strap and saddle member; and d. a spring washer mounted on said bolt between said bearing surfaces on said saddle member and said bolt head, said washer extending outwardly of said bolt head and broadly over said bridge of said saddle member, and effective when compressed by the tightening of said bolt to provide a continuous compressive force on said aluminum conductor to maintain a satisfactory electrical contact with said strap regardless of any tendency of said conductor or connector parts to deform under pressure.

2. a bridging section joining said leg sections and having a centrally located aperture and a flat bearing surface surrounding said aperture; c. a drawbolt retained in free-turning relation in said aperture in said saddle member and having,

2. a threaded aperture extending through said contact surface portion; b. an aluminum saddle member having,

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