Patent Publication Number: US-3967873-A

Title: Wire terminal electrical contact

Description:
BACKGROUND 
     The extensive commerical use of push-in type connectors started with the development by Benander of the invention of the U.S. Pat. Nos. 2,705,785 and 2,705,787. Numerous push-in type connectors followed this commercial success. Other patents of later vintage concerned with the push-in type connector and having two side-by-side cam contacts on the same strip of metal include the U.S. Pat. Nos. 3,339,170 and 3,467,941 assigned to the same assignee as this application. Also U.S. Pat. No. 3,489,985 discloses a contiguous cam contact for a convenience outlet which is in its structure quite similar to that disclosed in the subject application. 
     Other relevant patents are the U.S. Pat. Nos. 2,974,301; 3,001,168; and 3,325,768 which were cited as references in the U.S. Pat. No. 3,489,985 assigned to the same assignee as this application. 
     One problem which has developed in the employment of the electrical contact of the device taught in the U.S. Pat. No. 3,489,985 is that very close dimensions of the contiguous cams must be maintained in order to prevent or avoid interference of one cam with the other. Such interference is particularly disadventageous where it causes reduction of the gripping power of an adjoining cam on a wire so that less than a full pressure contact, and suitably low resistance, is maintained between the inserted wire and the wire contact. One problem encountered in use of the receptacle of the U.S. Pat. No. 3,489,985 patent with its eight push-in connectors, is that it could be used only with the smaller size wires normally employed in branch circuits in residences. With the introduction of the copper clad aluminum wire the contact itself could function perfectly well with the copper clad wire but the wire diameter required is frequently a No. 10 size wire and this wire cannot be accommodated in the contact push-in connector structure of the U.S. Pat. No. 3,489,985. 
     Accordingly a problem arose in attempting to maintain the compactness of structure so that the receptacle with eight push-in connectors could be used in home construction, where it has its principal application, and yet accommodate the larger size wires which were an incident of the change to copper clad aluminum conductors in the home building trade. 
     An effort was made to eliminate this problem by enlarging the two openings seen in the U.S. Pat. No. 3,489,985 to a single overall opening of oval shape so that two No. 10 wires could fit into the opening and make the proper contact with the metal strip within the receptacle. While this permitted larger wire entry and contact was successfully established with the inserted wires, it was found that where a No. 10 copper clad wire was employed in combination with a No. 12 or No. 14 copper or copper clad wire in the same opening and the wires were manipulated as a consequence of the insertion of the receptacle into its wall box where it was to be employed, the contact on the smaller diameter wire was sometimes reduced so that a high resistance contact developed or that the contact with the smaller diameter wires was in fact broken due to the insertion of the wired receptacle into its wall box. 
     SUMMARY OF THE INVENTION 
     In one of its broader embodiments, the wire terminal electrical contact of this invention includes an insulating housing with at least one metal strip having spring properties positioned in the housing adjacent a wall of the housing having wire entry ports. The strip is provided with an F configuration of slits to form two contiguous metal tongues. The end portions of the tongues are bent up away from the adjacent wall of the insulation housing to form wire contact cams. Wire entry ports through the adjacent wall of the insulation housing are aligned with the cam ends to permit contact of the cam ends by wires entering the ports. The two ports are generally rounded and large enough to accept a No. 10 gauge wire. Also the two ports interlock but the width of the interlocking portion of the ports is smaller than the diameter of larger diameter wires introduced into the ports and in fact smaller than the smaller diameter wires introduced into the ports. 
    
    
     DESCRIPTION OF THE DRAWINGS 
     The description which follows will be made clearer by reference to the following drawing in which: 
     FIG. 1 is a perspective view of a receptacle having an electrical wire terminal contact as provided pursuant to this invention; 
     FIG. 2 is a rear elevational view of the receptacle as illustrated in FIG. 1; 
     FIG. 3 is an internal view of the rear housing of the receptacle of FIG. 1 with the cover and mounting bracket and one contact strip removed; 
     FIG. 4 is a perspective view of a contact strip as employed in the receptacle of FIG. 1; 
     FIG. 5 is a detailed view of the interlocking openings or wire entry ports in the rear of the receptacle housing as viewed from the device exterior; 
     FIG. 6 is a perspective view of the detail as shown on FIG. 5 and illustrating two wires of different size poised for entry into the interlocking wire entry ports; 
     FIG. 7 is a sectional view through the detailed portion of the receptacle as illustrated in FIG. 6 showing a larger wire inserted in place through one of the interlocked wire entry ports and engaging the contact and locking tongue of the contact strip; 
     FIG. 8 is a view similar to that of FIG. 7 but illustrating a smaller wire inserted in position in the wire entry port similar to that illustrated in FIG. 7. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring to the drawing, a conventional receptacle is illustrated in perspective view in FIG. 1. It includes a mounting strap 10, which is mounted between a cover 12 and a base 14. These three elements are held together by means of screws 20 evident in FIG. 2 of the drawing. To assemble the receptacle device, electrical contact numbers 16 are placed in receiving contours, not shown, on the underside of the cover 12. A grounding contact, also not shown, may be mounted in a receiving channel between the electrical contacts 16 and in insulated relation thereto. The mounting strap 10 is superposed over and in electrical contact with the grounding contact and is held in place after assembly of the device due to a pressing of the base 14 against cover 12 under pressure developed by tightening screws 20. This construction is known and conventional and is not part of the invention herein. Much of the other conventional aspects of the construction is described in further detail in the issued U.S. Pat. No. 3,489,985 assigned to the same assignee as this application and covering aspects of invention not covered by this application. 
     The mounting holes 36 and 38 in the mounting strap 10 allow use of mounting screws in a manner well known in the art to secure and support the strap and the device mounted thereon into its proper posture in a wall box, not shown, of conventional configuration. The pairs of ears 40 are for use in facilitating mounting of an outlet flush to a wall in the wall box. Grounding of the strap of the device to a grounding wire or grounding box may be accomplished by attaching such grounding wire to grounding tab 48 by means of grounding screw 46. 
     Considering next the face 12 of the receptacle, it is also of conventional configuration and construction much as the conventional grounding strap already described. It includes the upper and lower pair of conventional slot openings 42 for conventional parallel blade contacts of electric plugs and includes the upper and lower grounding blade openings 44. A conventional wall plate, not shown, may be mounted over the receptacle and held in place by a screw, also not shown, threaded into the threaded opening 50 in the center of the face 12 of the receptacle. 
     The novelty of the present article resides more in the base element 14 of the receptacle and in cooperation of portions the base with portions of metal strip contacts mounted in the base. This portion of the device is an insulating housing base which will house the electrical contact strips 16 and which will receive the wires which supply electricity to the contact strips. Conveniently these contact strips may also be used in conducting electricity to additional pairs of wires also connected through the housing 14 to the current carrying contact 16 within the housing. 
     A contact 16 is seen in a perspective view in FIG. 4. It includes end blade contacts 22, pairs of wire contact cams 24, a central break of tab 26 for split circuit wiring and may include side screw terminals 28. Screws may be omitted from the contact strip in the form of product illustrated in FIGS. 2 and 3 where power supply is by push-in wire only. 
     One such contact 16 is also illustrated mounted in position in the interior of housing 14 in FIG. 3 where the housing is shown with the cover and bracket and grounding straps removed. Generally speaking, a very desirable feature of a receptacle which is used in both receiving wire for powering of the contact itself and in providing an additional capability of permitting the power to be conducted from the receptacle, and particularly from a contact strip 16 of a receptacle to other wiring devices, such as other outlets, is the compactness of the device which is employed for this purpose. One feature of the receptacle of the U.S. Pat. No. 3,489,985 referred to above is that the device itself is quite compact and yet there are four pairs of wire contact openings in the back of the device. This compactness is achieved partly because the contacts for the wire are of the push-in type and the cams which provide the electrical contact between the strip 16 and the contact are contiguous in the prior construction. An important element in the retention of the compactness of the receptacle of this application, and in particular the wire terminal electrical contact of the receptacle is the use of the contiguous cams in making contact with pairs of wires which are inserted through the respective openings in the rear of the base 14. In other words, what is important is that the device not be substantially enlarged from the size which was developed and patented in U.S. Pat. No. 3,489,985. 
     However, with the advent of copper clad aluminum wire, it was no longer feasible to use the rear push-in wire entry arrangements as taught in the U.S. Pat. No. 3,489,985 partly because the use of the copper clad aluminum wire involved use of larger diameter wires than were conventional in carrying branch circuit current of 15 or 20 amperes through solid copper wire. It has now been demonstrated, however, that through a combination of spacial arrangement of the access ports and means for restricting movement of even the smallest diameter wires, a problem of interference of one wire with another has been minimized and eliminated. 
     In this connection it was found that the device of the U.S. Pat. No. 3,489,985 would simply not work for solid copper clad wire of No. 10 gauge size. On the other hand, any effort to separate the contiguous cams would result in an enlargement of the overall device itself and retention of the small size of the device is important particularly where eight wires are to be used with the device and are to be located in the back of a conventional wall box. The wires themselves, when folded and pushed back into the box, occupy appreciable volume in the box. 
     To use the two contiguous cams as provided in U.S. Pat. No. 3,489,985 would permit retention of the compactness feature of the overall device. 
     In this connection it was found that while the device of this invention provides access for eight wires with rear entry ports, that where two wires were combined in a pair of ports and the opening was enlarged sufficiently to permit the wire to enter at any point to the rear of the cams, the movement of the receptacle with several wires back into the wall box can cause two wires to move in such fashion that a larger wire would bear against the cam which had locked a smaller wire and the bending back of the second cam by the longer wire would prevent a suitable contact between the smaller wire and the contact strip 16. Also a smaller wire could escape from its cam and take up residence in the larger space in the cam opening holding the larger wire. 
     The manner in which such interference of larger and smaller wires is overcome is illustrated in the entry of larger and smaller wires as well as the different positioning of the cams when the larger and smaller wires are employed in connection with the contacting cams. Thus in FIG. 6 there are two wires 52 and 54 shown poised for entry into the wire terminal electrical contact of this invention. On the right is a larger wire 54 which may be a copper clad aluminum wire of No. 10 gauge and on the left is a smaller diameter wire 52 which may be a solid copper wire of No. 12 or No. 14 gauge. The two wire entry ports 62 and 64 are side-by-side and are interlocked where the two circular forms overlap. Yet the two interlocking wire entry ports 62 and 64 retain their identity partly because of the separating detents 66 and 68. A rectangular cam release port 70 of conventional form is adjacent the wire entry ports and permits access to the locking cams to release the wires 52 and 54 in a manner well known in the art. 
     Two interlocked wire entry ports 56 and 58 are formed and provided in the back of housing 14 in a position adjacent wire locking cams 60 and 62 of contact strip 16 in base 14 as illustrated in FIG. 3. 
     In FIG. 7 the contact of the larger diameter copper clad aluminum wire 54 with the cam 56 is illustrated and it is evident that the cam 56 is bent back to a large degree. By contrast, in FIG. 8 the smaller diameter copper core wire 52 is shown in its position within the receptacle base 14 and bearing against the cam 58 in fashion similar to that shown in FIG. 7. Accordingly, where a wire 54 such as that shown in FIG. 7 is deflecting a cam 56 of the pair of contiguous cams of the strip 16 and the second of the contiguous cams 58 is bearing against a smaller diameter wire as a No. 14 gauge wire 52, there would be a separation of contact of the cam 58 from the No. 14 gauge wire 52 if the larger diameter wire did bear against the cam 58 supporting and contacting and gripping the smaller diameter wire 52. 
     Again an important point here is the retention of the compactness which is made feasible by the contiguous cam arrangement of the U.S. Pat. No. 3,489,985. 
     Where the two openings were combined into a single large opening, an interference of the two wires was found to occur and contact pressure of the second of a pair of cams was reduced or broken. 
     However, a distinct advantage of retention of the compactness of the overall wiring device structure, particularly a compactness of the wire terminal electrical contact of this invention was made possible by employing in combination with the contiguous cams, a pair of wire entry ports which each had sufficient size to permit entry of the largest diameter wire, but which were in part separated by an interlocking of the two side-by-side round openings. By this combination, a smaller wire is prevented from escaping from its cam as the device is manipulated and faining the larger wire. Also the larger wire is prevented from bearing on a cam holding a smaller wire to deflect the cam and loosen its grip on the smaller wire.