Self-grounding Receptacle

Abstract

An electrical device is secured within an outlet box by means of a fastener passed through an opening in a mounting strap on the device and into the outlet box. A U-shaped metal grounding clip embraces an edge of the strap adjacent the opening therein and presents two spaced portions located on opposite faces of the strap in position to engage the fastener and establish an effective grounding connection between the electrical device and the outlet box through the mounting strap and fastener.

Description

FIELD OF INVENTION

It is generally necessary under present codes relating to the installation of electrical devices to require the device to be grounded. For this purpose it has been common practice to provide the device with an electrical connection extending from the device to a grounded outlet box in which the device is mounted. However, the use of a separate binding post on the device together with an extra wire connected to the outlet box or other grounding means not only increases the cost of the device but also requires extra time consuming operations which increase the cost of installing the device in a building or elsewhere. It has therefore been suggested that the electrical device be provided with a grounding clip or other means engageable with the fastening means or screw by which the electrical device is mounted in the outlet box. Typical devices of this type are disclosed in U.S. Pat. No. 3,403,214; No. 3,432,793; No. 3,440,590; and No. 3,526,703.

However, the constructions thus provided are somewhat complicated and expensive in that they call for special construction or modification of the mounting strap, outlet box or fasteners used in the assembly. Moreover, the contact between the fastening means and the grounding clip and mounting strap is frequently rather loose and does not always serve to establish an adequate electrical path to assure an effective grounding connection.

In accordance with the present invention, these objections and limitations inherent in devices of the prior art are overcome and means are provided for use with conventional forms of electrical devices, outlet boxes and fasteners which assure effective grounding of the device at a minimum expense and without requiring any additional operations on the part of the person installing the electrical device.

These results are preferably attained by providing a grounding clip which may be produced as a separate element for application to a conventional mounting strip of an electrical device. The grounding clip is then secured to the mounting strap by a conventional fastener used to secure the device in place within a conventional outlet box. The grounding clip preferably is generally U-shaped in cross-section and may be applied to the mounting strap so as to embrace an edge thereof while presenting portions located adjacent opposite faces of the strap. One of said portions is designed to be engaged by the head of a fastener used to secure the device in place within an outlet box while the other portion engages the shank or threaded portion of the fastener to establish an effective grounding connection from the device through the mounting strap and fastener to the grounded outlet box.

THE DRAWING

FIG. 1 is a front elevation of a typical electrical device mounted in an outlet box and having a mounting strap with one form of grounding clip embodying the present invention applied thereto;

FIG. 2 is an enlarged detail sectional view substantially on line 2--2 of FIG. 1;

FIG. 3 is a still further enlarged front elevation of the grounding clip of FIG. 1;

FIG. 4 is a side elevation, on the same scale as FIG. 3, of the grounding clip illustrated in FIGS. 1, 2, and 3;

FIG. 5 is an enlarged detail sectional view on line 5--5 of FIG. 2; and

FIG. 6 is an enlarged detail sectional view on the same cutting plane as FIG. 2, substantially on line 6--6 of FIG. 5.

In that form of the invention chosen for purposes of illustration in the drawings the electrical device 2 is shown as a conventional electrical receptacle designed to receive a three-prong plug 4 having current carrying prongs 6 and a grounding prong 8 electrically connected to the mounting strap 10 of the device by any suitable means (not shown). The device 2 may in the alternative be a switch or any other device of the type designed to be mounted within a conventional grounded outlet box 12 by fasteners 14 passed through openings 16 in the mounting strap 10 and into retaining engagement with the outlet box.

In order to establish an effective grounding connection between the device 2 and the outlet box 12 through the mounting strap 10 and fasteners 14, a grounding clip 18 is applied to the mounting strap 10 and held in place thereon by the fastener 14.

As shown in FIGS. 2 and 4, the grounding clip 18 may comprise a spring member generally U-shaped in cross-section so as to present two leg portions 20 and 22 adapted to be located adjacent opposite faces of the mounting strap 10. The clip may be applied to any conventional mounting strap of an electrical device so as to embrace an edge thereof whether the mounting strap has the usual plaster engaging ears 24 or not. The portion 20 of the clip 18 is located adjacent the outer face of the mounting strap 10 and has an opening 26 therein designed to be positioned in registry with the opening 16 in the mounting strap. The portion 22 of the grounding clip 18 is located adjacent the inner face of the mounting strap 10 and has an opening 28 therein aligned with the opening 26 in the portion 20 of the clip. The fastener 14 then can be passed through the opening 26 in the portion 20 of the clip, the opening 16 in the mounting strap 10 and the opening 28 in the portion 22 of the clip 18. In this way the fastener 14 serves to secure the grounding clip 18 to the mounting strap 10 to hold it in place during shipment and handling of the device even before it is mounted in the outlet box.

The fasteners employed in mounting the electrical device within an outlet box are generally provided with a head as shown at 30 and the opening 28 in the portion 22 of the grounding clip 18 is made to be large enough to permit the shank 32 of the fastener 14 to pass freely therethrough. On the other hand, the opening 26 of the portion 20 of the clip is formed to assure positive and intimate contact between the clip 18 and the fastener 14. For this purpose, the portion 20 of the clip is preferably slotted longitudinally from end to end thereof as shown at 34 to provide two spaced elements 36 and 38 lying in the same general plane, each of which is formed with tongues 40 extending inwardly about the opening 26. The size of the opening 26 is somewhat less than that of the shank 32 of the fastener so that when the fastener is passed through the opening 28 the elements 36 and 38 will be forced apart in said plane and the tongues 40 thereon will be urged into positive and firm electrical contact with the fastener and between the threads on the shank of the fastener. The fastener is threadedly engaged in the opening of the ear 41 of the outlet box, and can be advanced therein, if desired, to an extent where the frusto-conical head 30 of the fastener engages in the opening 26, forcing the tongues 40 still further apart and assuring contact between the clip and fastener.

With this construction the operation of screwing the fastener 14 into retaining engagement with the outlet box 12 in mounting the electrical device 2 in the outlet box, will serve to force the head 30 of the screw into positive and firm contact with the portion 20 of the clip 18 whereas the tongues 40 of the portion 22 of the clip will positively and firmly engage the shank 32 of the fastener. In this way, an effective grounding connection is established from the grounding prong 8 of the plug 4, through the mounting strap 10 and clip 18, to the fastener 14 and the grounded outlet box 12.

Further, it is desirable for the grounding clip to be formed so that the lower parts of the portions 20 and 22 thereof are inclined toward each other so that they are normally spaced apart a distance less than the thickness of the mounting strap 10. The lower or free end of one end of at least one of said portions, such as the portion 22, may then be reversely inclined outwardly as shown at 42 to facilitate application of the clip to the strap. The portions 20 and 22 then have a sprung engagement with the strap 10 and bear forcibly against the opposite faces of the strap in the area 44 below the fastening means. In this way an effective grounding connection between the clip and strap is assured even though the clip may be cocked or otherwise displaced on the strap during handling thereof or upon application of the fastening means to the clip and strap.

In order to assure an effective grounding connection between the fastener and the outlet box, it is sometimes desirable to employ a threaded fastener which will provide a firm, frictional contact with the threaded element on the outlet box such as the threaded ear 46 formed integral with the box 12. For this purpose, the fastener 14 may consist of a screw having longitudinally extending grooves 48 in the shank 32 thereof. The edges of such grooves and the resulting slight distortion of the threads then tend to cause the fastener to bind against the threads in the ear of the outlet box whereby a positive grounding connection is established. However, other types of headed fasteners may be employed if desired.

The outlet box may be of any conventional type such as a flush type or wall mounted box and the electrical device mounted in the box may be a receptacle, switch or other unit of a conventional character.

The size, shape and configuration of the grounding clip are capable of many variations for use with different sizes and types of electrical wiring devices. In view thereof, it should be understood that the particular embodiment of the invention shown in the drawing and described above has been chosen for purposes of illustration only and is not intended to limit the scope of the invention as defined by the following claims.

Claims

We claim:

1. A clip effecting a low-resistance electrical connection between the mounting strap of an electrical wiring device and an outlet box threadedly engageable by a mounting screw whereby the device is mounted in the box, comprising an electrically conductive spring member formed in the shape of a U and disposed astride an edge of the strap, said member having opposed leg portions which resiliently spread into clamping engagement with opposite faces of the strap whereby to establish a low-resistance electrical connection between said member and the strap, at least one of said leg portions comprising a pair of elemenets disposed in side-by-side relation in the same general plane and resiliently spread in said plane so as to be biased apart by, and form a low resistance electrical contact with, a mounting screw extending therebetween into threaded engagement with the outlet box.

2. A clip as in claim 1, wherein said elements are spaced apart to receive the mounting screw, the space between the elements extending fully from end to end of said one portion of the spring member.

3. A clip as in claim 2, wherein said one portion has an opening communicating with said space between the elements to accommodate the mounting screw, said elements presenting a series of tongues angularly spaced about said opening, said tongues extending inwardly of the opening so as to be urged into firm electrical contact with the mounting screw when the elements are biased apart by the screw.

4. A clip as in claim 3, said one portion having a free end, said member including a connecting part extending between and integrally joining said opposed portions thereof, the space between said elements extending fully from the connecting part to, and opening upon, the free end of said one portion of the member, whereby said one portion is wholly divided into said elements.

5. A clip as in claim 4 wherein said space is continued through the connecting part to the other portion, providing each element with a separate, individual connection to said other portion, each element being movable about said individual connection in said general plane of the elements, away from the other element responsive to the insertion of the mounting screw therebetween.

6. A clip effecting a low resistance electrical connection between the mounting strap of an electrical wiring device and outlet box threadedly engageable by a mounting screw whereby the device is mounted in the box, comprising a member of flat spring metal material formed to include a pair of side-by-side elements transversely spaced apart and lying in the same general plane, said member including a portion to which both of said elements are separately connected at one end of the elements, under spring tension tending to bias the elements toward said portion in a direction generally normal to said plane, whereby the elements clampably engage the mounting strap between said portion and the elements to effect a low resistance electrical connection between the strap and the member, said elements being further connected to said portion for and yieldingly moved away from each other in said plane in response to the extension of a mounting screw through said space, having a diameter greater than the normal width of the space for effecting a low resistance electrical contact between the screw and the respective elements.

7. A clip as in claim 6, in which said member is formed with an opening constituting an enlargement of the space between the elements, said elements presenting a series of edges angularly spaced about said opening to provide the points of contact between the screw and the respective elements.

8. A clip as in claim 7 in which said portion is formed with an opening in registration with but larger in size than the opening between the elements, for passage of said screw through the last named opening without engaging said portion.