Resilient Electrical Terminal Connector

Abstract

A connector for making electrical connection between a terminal strap and a wire conductor, particularly an aluminum conductor, comprises a rigid, rectangular frame having a central opening. A bolt, having a clamping plate mounted to its free end, is threadingly advanced into the frame opening to engage and clamp the wire conductor in electrically connecting relation with the terminal strap. A lost-motion coupling incorporated in the clamping force train between the clamping plate and the frame is equipped with a spring to provide resilient clamping pressure on the current carrying parts.

Description

BACKGROUND OF THE INVENTION

Heretofore problems have been experienced in making lasting electrical connections between wires and flat terminal straps commonly used in various electrical devices, such as, for example, molded case circuit breakers, switches, relays, etc., particularly when one or both of the current carrying parts is formed of aluminum. These problems are becoming more widespread as the electrical industry increasingly resorts to the use of aluminum for current carrying parts due to the shortage and high cost of copper. The conventional, rigid clamping connectors, while generally quite successful for connecting copper conductors, are not entirely satisfactory for aluminum or other relatively soft material conductors due to their tendency to "cold flow" or plasticly deform under the compressing clamping forces. This permanent deformation, in time, adversely affects the mechanical and electrical connection between the current carrying parts. Connectors described as being effective in overcoming this problem are disclosed in U.S. Pat. No. 2,771,591 and in my co-pending application, Ser. No. 347,127, filed Apr. 2, 1973 and assigned to the assignee of this application.

When using clamping connectors with aluminum wire, the wire tends to assume a permanently flat cross-sectional configuration and thus in time becomes loosened mechanically and less intimately connected electrically. Similarly, if the wire is clamped against a terminal strap which is also formed of aluminum or surface coated with aluminum or other relatively soft metal, the compressive effect of the wire on the strap can cause material flow outwardly from under the wire, thus further jeopardizing the connection. Due to the desirable heat transfer and dissipation properties of aluminum, the connector parts are advantageously also formed of aluminum. However, here too the clamping forces can cause deformation of the connector parts, with a consequent relaxation in the contacting pressure between the wire and terminal strap. Any significant relaxation in the contact pressure between current carrying aluminum parts accelerates the formation of highly resistive oxide films, thus greatly reducing effective life of the connection.

Furthermore, connectors embodied as terminal connectors for molded case circuit breakers, switches and the like, must be compact as space is often a premium. For example, in certain molded case circuit breakers, the lateral dimensions of the terminal straps must, owing to available space, be minimized, as must the corresponding dimensions of the terminal connector. Yet, it is desirable to maximize the opening in the connector for receiving the wire to provide greater choice in the wire size that can be employed.

Still further, it is desirable and, in fact essential from a salability standpoint, that the parts of the connector be adapted for cooperating in a manner which facilitates the making of a dependable initial electrical connection in a rapid manner and for minimizing any undesirable relative motion between the connector parts and the current carrying parts which could adversely affect the useful life of the connection.

It is accordingly an object of the present invention to provide an electrical connector adapted for assuring a reliable electrical connection between current carrying parts, wherein at least one of the parts is formed of aluminum or other relatively soft, plasticly deformable metal.

Another object of the present invention is to provide an electrical connector of the above character which is capable of providing a dependable electrical connection of relatively long life.

Still another object of the present invention is to provide an electrical connector of the above character embodied as a terminal connector for molded case circuit breakers and the like, wherein the connector is compact in size, inexpensive to manufacture, and conveniently operable in a rapid manner.

Other objects of the invention will in part be obvious and in part appear hereinafter.

SUMMARY OF THE INVENTION

In accordance with the present invention, there is provided an electrical connector which is particularly adapted as a terminal connector for molded case circuit breakers, switches, and the like, wherein the conductor to be connected is formed of aluminum or other soft, readily plasticly deformable metal. Generally stated, the electrical connector of the present invention includes a rigid frame having walls defining a central opening for receiving the bared end of a wire conductor to be connected. A clamping bolt having a free end to which is mounted a clamping plate is threadingly advanced into the frame opening through one of the walls to bring the plate into clamping engagement with the wire conductor, thus to electrically connect the wire conductor with a terminal strap of the circuit breaker, etc.

The electrical connector further includes, in accordance with the invention, the incorporation of a lost-motion coupling in the clamping force train between the clamping plate and the frame. A spring element is incorporated in this lost-motion coupling such that the clamping force exerted on the current carrying parts is resilient in character. As a consequence, any cold flow or plastic deformation of the current carrying parts of the electrical connection, which would otherwise result in a lessening of the contact pressure therebetween, is taken up by the resilient lost-motion coupling. As a consequence, the integrity of the electrical connection is preserved over a longer useful life than would otherwise be possible.

In one embodiment of the invention, the clamping bolt is threadingly advanced through a sleeve mounted in an aperture formed in one of the frame walls. The resilient lost-motion coupling of the invention is provided in the mounting of the sleeve to the frame.

In another embodiment of the invention, the resilient lost-motion coupling is provided in the mounting of the clamping plate to the clamping bolt.

In still another embodiment of the invention, the resilient lost-motion coupling of the invention is provided in the connection of the terminal strap to the frame; the wire conductor being clamped against the terminal strap by the advancement of the clamping bolt and clamping plate into the frame opening.

In all embodiments of the invention, the clamping force providing the requisite continuing contact pressure between the current carrying parts is provided by the resilient lost-motion coupling included in the clamping force train between the clamping plate and frame.

The invention accordingly comprises the features of constructions, combinations of elements and arrangements of parts which will be exemplified in the constructions hereinafter set forth, and the scope of the invention will be indicated in the claims.

For a fuller understanding of the nature and objects of the invention, reference should be had to the following detailed description taken in connection with the accompanying drawing, in which:

FIG. 1 is a side elevational view, partially in section, depicting one embodiment of the invention;

FIG. 2 is a side elevational view, partially broken away, of another embodiment of the invention;

FIG. 3 is a side elevational, sectional view of still another embodiment of the invention; and

FIG. 4 is a sectional view taken along line 4--4 of FIG. 3.

DETAILED DESCRIPTION

The embodiments of the invention shown in FIGS. 1 through 3 are for the purpose of effecting an electrical connection between a flat terminal strap 10 and a wire conductor 12. The strap is elongated, rectangular in cross section, and typical of the terminal straps used in many electrical devices, such as molded case circuit breakers, switches, relays, and the like. The wire conductor 12 may be a single conductor, as shown in FIGS. 2 and 3, or a multi-strand conductor, as illustrated in FIG. 1. As will become apparent from the following detailed description, the electrical connector embodiments of the present invention are most advantageously employed when the wire conductor and/or the strap is formed of aluminum or other, readily plasticly deformable conductive metals.

In the embodiment of the invention seen in FIG. 1, the electrical connector includes a rectangular frame 14 having top, bottom and sidewalls defining a central opening 16 into which terminal strap 10 and wire conductor 12 are introduced. If desired, strap 10 may be suitably configured so as to be captured within central opening 16 or attached to the frame bottom wall or floor 18 so as to be maintained in place prior to effecting the electrical connection. Top wall 20 is provided with an opening 21 for receiving a sleeve 22. This sleeve is flanged at its lower end, as indicated at 24, and staked over at its upper end, as indicated at 26, so as to be mounted to the frame while permitting a limited degree of relative or lost motion therebetween. Taking up the slack in this lost motion connection is a suitable spring, such as a spring washer 29, acting between the flanged portion 24 of sleeve 22 and the top wall 20 of frame 14. The central bore of sleeve 22 is threaded to accommodate the advancement of a clamping bolt 28 into the central opening of frame 14. An arcuate clamping plate 30, freely rotatably mounted on the end of clamping bolt 28, is provided to clamp terminal strap 10 and wire conductor 12 against the floor 18 of frame 14, pursuant to effecting the electrical connection therebetween.

From the foregoing description of FIG. 1, it is seen that as the clamping bolt 28 is turned down to exert clamping pressure on the wire conductor 12 and terminal strap 10, spring 29 is compressed. Once the desired contact pressure between wire conductor 12 and terminal strap 10 is achieved by clamping bolt 28, the resiliency of the clamping force generated by spring 29 is effective to maintain the contact pressure between the terminal strap and wire conductor relatively constant despite deformation of either or both of these current carrying parts.

In the embodiment of the invention seen in FIG. 2, terminal strap 10 is provided with a tapped hole 34 into which is threaded the end of a bolt 36 having an enlarged diameter intermediate portion 38 slidingly received in an opening 40 formed in the bottom wall or floor 42 of a generally rectangular frame 44. A spring washer 46 is positioned to operate between busbar 10 and the floor 42 of frame 44. A clamping screw 48 is threaded through a tapped hole 50 in the top wall 52 of frame 44 to advance a bi-planar clamping plate 54, rotatably mounted to the free end thereof, downwardly to resiliently press the wire conductor 12 against the terminal strap 10. It is seen that the resilient lost-motion connection afforded by bolt 36 slidingly mounted by frame 44 and spring washer 46 acts in the clamping force train to maintain the requisite continuing contact pressure between terminal strap 10 and wire conductor 12 despite plastic deformation in either of these current carrying parts.

In the embodiment of the invention seen in FIG. 3, the terminal strap 10 is secured in electrical contacting engagement with the bottom surface of the floor 60 of an open interior electrically conductive frame 62 by a bolted connection afforded by bolt 64. The top wall 66 of frame 62 is provided with a threaded bore 68 in which is threaded a clamping bolt 70. Clamping bolt 70 is provided with a stepped, axial bore having a reduced diameter portion 72 in which is received a rod 74 carrying at its lower end a clamping plate 76. The upper end of rod 74 is staked, as indicated at 78, so as to connect the clamping plate to the end of clamping screw 70 with a limited degree of lost or relative motion accommodated therebetween. A spring washer 80 is positioned between the clamping plate 76 and the lower end of clamping screw 70. The upper end of the axial bore through clamping screw 70 is formed with a hex socket 82 accommodating a wrench for advancing the clamping plate 76 into clamping engagement with wire 12. Spring 80 acts to maintain the requisite contact pressure between the wire conductor and the floor 60 of frame 62, thus insuring a lasting electrical connection with terminal strap 10. As seen in FIG. 4, rod 74 and bore 72 may be rectangular in crosssection, such that the clamping plate 76 rotates with clamping bolt 70. This produces a beneficial wiping action on wire conductor 12 to remove surface oxides, thus insuring a good current path through the clamping plate, rod, clamping bolt and frame body to the terminal strap to supplement the more direct current path through the floor 60 of the frame.

In any of the various embodiments of the invention, 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 connector parts of aluminum also, all for the purpose of enhancing thermal and electrical conductivity, achieving weight and material cost savings, and avoiding corrosion due to galvanic action. Using the same material for the terminal strap, wire conductor and connector also affords greater uniformity in the coefficients of expansion of the various parts and thus minimizes the effects of differences in the thermal expansion and contraction of the parts. It is anticipated, however, that the resilient clamping force afforded by the present invention will compensate for the otherwise prejudicial effects of thermal expansion and contraction of the parts on the integrity of the electrical connection.

It will be observed from the foregoing detailed description and the accompanying drawings that the electrical connector of the present invention is quite compact in size, taking up virtually no more space than is consumed by conventional terminal connectors. Consequently, the terminal connector embodiments disclosed herein may be readily accommodated in the confined spaces being allotted for terminal connectors in currently available molded case circuit breakers, switches, and the like. Moreover, the making of electrical connections during installation by an electrician using the terminal connectors of the present invention is as straightforward and convenient as with conventional terminal connectors exerting rigid clamping forces.

It will thus be seen that the objects set forth above, among those made apparent from the preceding description, are efficiently attained and, since certain changes may be made in the above constructions without departing from the scope of the invention, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

Having described my invention, what I claim as new and desire to secure by Letters Patent is:

Claims

1. A terminal connector for making an electrical connection between a terminal strap and a wire conductor, said connector comprising, in combination:

A. a rigid frame having a central opening and means forming an aperture through a wall of said frame into said central opening;

B. a sleeve accommodated in said wall aperture, said sleeve having a threaded axial bore and terminating in inner and outer axially spaced, radially extending flanges, said flanges engaging said wall about said aperture to capture said sleeve in said wall aperture and to limit the degree of reciprocal motion of said sleeve through said wall aperture;

C. a clamping bolt threadedly engaged in said axial bore to advance a free end thereof into said central opening;

D. a clamping plate mounted by said free end of said bolt for clamping a wire conductor introduced into said central opening in electrical connection with a terminal strap therein; and

E. a spring positioned within said central opening and acting between said inner flange of said sleeve and said frame to exert a resilient clamping force on the wire conductor.