Electrical Grounding Receptacle

Abstract

An electrical grounding receptacle is provided with means to insure that, upon insertion of a conventional three-pronged plug, contact between the grounding prong and the grounding contact is made before any contact can be made to the power contacts. The structure includes female contact elements within a housing including a grounding contact that has a portion extending within an opening of the front face in which the plug blade is received while the power contacts are disposed entirely below their corresponding openings in the front face.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to electrical receptacles, such as for convenience outlets, and particularly to those for three-wire attachment and mating with a three-pronged plug wherein a grounding instrumentality is provided.

2. Description of the Prior Art

Grounding receptacles are in widespread use, often in the form of duplex receptacles, that include provision for receiving two blades of a plug that in use carry the electrical power and a third blade for purposes of grounding the appliance or other instrumentality to which the plug is connected. Such plugs and receptacles generally provide greater safety than corresponding devices that only include the power blades and contacts. The configuration of such plugs and receptacles is limited in that there are industry standards establishing the general nature of the devices and limits on the dimensions of various elements thereof. Such standards have been adopted by various governmental agencies.

NEMA standard 5-15-1961 for "Plugs and Receptacles-- General Purpose, 125 volts, 15 amperes, 2 pole, 3 wire, grounding type" is an example of an industry standard for the type of receptacles to which the present invention is applicable.

It has been found in rare occurrences that, with a receptacle of the type described that complies with the established standards, it is possible for a user to insert a plug in such a peculiar manner that contact is made between the power prongs of the plug and the power contacts of the receptacle before any contact is made between the grounding prong of the plug and the grounding contact of the receptacle. This is despite the fact that the grounding blade of the plug is required to be at least 0.125 inch longer than the power blades of the plug. Thus a user may assume that the use of a three-pronged plug and mating receptacle provides a measure of safety which is in fact absent. The hazard is found most likely to occur when the plug is inserted in a manner that it is tilted away from the grounding contacts, particularly with some slight lateral bending of the blades.

It is apparent that the above-mentioned hazard could be avoided by greater restriction on the dimensions of the openings of the receptacle within which the plug blades are inserted, so as to more closely confine them and require the user to insert the plug with all the blades more nearly perpendicular to the face of the receptacle. However, the above referred to standards establish minimum dimensions for these openings, as well as maximum dimensions, and even with such minimum dimensions there is a possibility of the described hazard.

By way of further background, reference may be made to Howells U.S. Pat. No. 3,032,736, May 1, 1962, for a description of some receptacles of the general type to which the present invention applies.

SUMMARY OF THE INVENTION

This invention provides a receptacle that avoids the hazard of having hot plug contact made before grounding contact is made in the three-wire grounding-type receptacles, including those that satisfy prevailing industry standards, with only a modest change in structural design that can be readily and economically implemented by the manufacturer and without imposing any higher degree of care on the part of the user or other disadvantage.

The invention provides these advantages in a receptacle having a housing that includes a first portion of insulating material in which are contained a pair of mutually insulated power contact elements. The housing also includes means for containing a grounding contact, typically connected with a metal yoke that provides ultimate connection to an electrical ground. The housing has a front face with openings therein communicating to the contained contacts and for receiving the blades of a mating plug. The power contact elements are disposed entirely below the openings in the front face of the housing while the grounding contact includes a portion that extends within the opening of the front face so that insertion of a plug at any angle requires initial contact with the grounding contact of the receptacle.

In a conventional receptacle, the grounding contact is a U-shaped element that fits within a pocket formed by the insulating portion of the housing and a metal yoke in a manner such that the grounding contact is in electrical connection with the yoke at the bottom of the U-shaped portion. In accordance with this invention, one leg of the U-shaped grounding contact is made elongated to extend within the front face opening. Preferably, this extended portion of the grounding contact terminates at approximately the plane of the exposed front face.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a partial cross-sectional view of a receptacle in accordance with the prior art, with a mating plug, to illustrate the problem to which the present invention is directed;

FIG. 2 is a perspective view of a receptacle in accordance with the present invention; and

FIG. 3 is an elevation view, partly in cross section, of the structure of FIG. 2 with a mating plug illustrated to show solution of the problem to which the invention is directed.

DESCRIPTION OF THE PREFERRED EMBODIMENT

By way of further background to the present invention, reference is made to FIG. 1 to illustrate how a problem can arise in the use of prior art receptacles. Such a receptacle 10 includes an insulating housing 12 containing power contact elements 14 communicating with screw terminals 16 for wire attachment. The receptacle 10 also contains a U-shaped grounding contact 18 in electrical connection with a metal yoke 20. Upon the insertion of a three-pronged plug 22 having power blades 24 and a grounding blade 26, it is possible to make initial contact with power contacts 14 of the receptacle 10. While such manner of insertion is neither usual nor frequent, it does expose the user to an obvious risk which is desirably avoided.

In a device in accordance with this invention, as shown in FIGS. 2 and 3, the receptacle 30 includes a housing that comprises a first portion 32 of insulating material which contains mutually insulated power contacts 34 (only one of which is shown) in a manner that they connect with screw terminals 36 laterally disposed for connection with wires. The receptacle 30 also includes a generally U-shaped grounding contact member 38 in electrical connection with a metal yoke 40. The yoke 40 effectively forms part of the housing and with insulating portion 32 provides a pocket 42 in which the contact member 38 is contained. Openings 44 and 48 in front face 50 of the housing insulating portion 32 provide plug access with the power contacts 34 and ground contact 38, respectively. For simplicity in the drawing, some details of conventional elements in the structure are omitted. It is particularly desirable that the invention be applicable to otherwise standard configurations with only slight change. The invention is shown embodied in a duplex receptacle, only one-half of which will be specifically described. While the general configuration of receptacle 30 is conventional, this is merely by way of example as the invention may be carried out in other forms.

The improvement which is sought is provided by having a first leg 38A of the U-shaped ground contact 38 extended to within the opening 48 provided in the front wall or face 50 of the receptacle 30. The power contacts 34 are disposed below the openings 44 in the front face 50. An inserted plug 22 (FIG. 3) is thus required to make contact between ground blade 26 and ground contact 38 before "hot" contact is made between blades 24 and contacts 34.

In the example shown, the receptacle 30 includes a feature shown in Howells U.S. Pat. No. 3,032,736, in that opening 48 for the ground contact is in the form of an elongated slot with a cross section that is arcuate on one side and open on the other side. Insulating member 32 may, if desired, have a wall at the illustrated open side of opening 48. However, such a wall is subject to breakage and is preferably avoided. The invention is, of course, applicable to receptacles with or without such a wall.

The extent of leg 38A of ground contact 38 may be varied in accordance with the extent of the power contacts 34, the size of openings 44 and 48 (in relation to plug blades 24 and 26), as well as other factors, while still performing its intended function. Conveniently, in generally standard receptacles as described, leg 38A may extend to approximately the same plane as the front face 50 while the power contacts 34 terminate below or at the plane of the innermost wall surface 51. Typically, therefore, there is a difference of about 0.25 inch between the extremities of elements 38A and 34 in devices in accordance with the exemplary embodiment of the invention.

Claims

I claim:

1. An electrical grounding receptacle comprising: a housing comprising a first portion of insulating material and containing a pair of mutually insulated power contact elements and a grounding contact; said housing having a front with a plurality of openings therein to receive blades of a plug and connect said blades with said grounding and power contact elements; said power contact elements being entirely disposed below said front face; said grounding contact having a portion thereof extending within an opening in said front face so insertion of a plug at any angle requires initial contact with said grounding contact; said housing also comprising a metal yoke which with said first portion forms a pocket for containing said grounding contact in electrical connection with said yoke; said grounding contact having a generally U-shaped structure with said portion extending within an opening of said front face being a first leg of said U-shaped structure, said first leg being adjacent an upstanding portion of said yoke and effectively restricting, to an extent greater than said first portion and said metal yoke alone, said opening for receiving a plug blade, said U-shaped structure having a second leg adjacent said first portion of said housing and shorter than said first leg.

2. The subject matter of claim 1 wherein: said first leg has an extremity terminating substantially at the plane of said front face.