US3699285A

US3699285A - Safety electrical receptacle

Info

Publication number: US3699285A
Application number: US72190A
Authority: US
Inventors: Ralph W Leatherman
Original assignee: Individual
Current assignee: Individual
Priority date: 1970-09-14
Filing date: 1970-09-14
Publication date: 1972-10-17
Anticipated expiration: 1989-10-17

Abstract

A safety electrical receptacle of the type receiving three wire grounding plugs, wherein the electrical circuit between the power supply terminal and the corresponding contact, to which the line voltage is fed, is normally open. Insertion of the grounding prong of the plug into the ground opening urges a movable portion of the corresponding contact into engagement with a fixed contact connected to the power supply terminal, thereby completing the electrical circuit from the terminal through the electrical contact elements and into the attachment plug blade. In one embodiment the grounding prong of the plug includes a tapered insulating jacket therearound to facilitate operation of the movable portion of the contact.

Description

United States Patent Leatherman [54] SAFETY ELECTRICAL RECEPTACLE [72] Inventor: Ralph W. Leatherman, Vale, NC.

[73] Assignees: Glenn Bingham, Lawndale; Ken Mayhew, Cherryville; Henry Ritchie, Cleveland; Hugh Leatherman, Florence, all of, NC. part interest to each [22] Filed: Sept. 14, 1970 211 Appl. No.: 72,190

Related U.S. Application Data {63] Continuation-in-part of Ser. No. 18,219, March 10, 1970, abandoned.

[52] U.S. Cl. ..200/51.09, 174/51, 339/14 [51] Int. Cl. ..H01v 33/30 [58] Field of Search ..200/51.0751.09; 339/14; 174/51 [56] References Cited UNITED STATES PATENTS 2,540,496 2/1951 Sperrazza ..200/5l.09 2,751,567 6/1956 Bissell et al ..200/51.09

[4 1 Oct. 17,1972

FOREIGN PATENTS ORAPPLICATIONS 438,031 11/1935 Great Britain ..200/51.09 509,021 1/1955 Canada ..200/51.09 222,210 1/1958 Australia ..200/51.09 130,049 1/1947 Australia "339/14 Primary ExaminerDavid Smith, Jr. Attorney-Hunt, Heard & Rhodes 5 7] ABSTRACT A safety electrical receptacle of the type receiving three wire grounding plugs, wherein the electrical circuit between the power supply terminal and the corresponding contact, to which the line voltage is fed, is normally open. Insertion of the grounding prong of the plug into the ground opening urges a movable portion of the corresponding contact into engagement with a fixed contact connected to the power supply terminal, thereby completing the electrical circuit from the terminal through the electrical contact elements and into the attachment plug blade. In one embodiment the grounding prong of the plug includes a tapered insulating jacket therearound to facilitate operation of the movable portion of the contact.

5 Claims, 8 Drawing Figures PATENTEDucI 17 I972 3.699.285

sum 1 or 2 Fl 3 INVENTOR RALPH W. LEATHERMAN ATTORNEY SAFETY ELECTRICAL RECEPTACLE REFERENCE TO RELATED APPLICATIONS The present application is a Continuation-In-Part of 5 applicants copending application Ser. No. 18,219, filed Mar. 10, 1970 and now abandoned.

BACKGROUND OF THE INVENTION Electrical receptacles, and more particularly grounded duplex conveniences receptacles, have become commonplace in todays environment. However, the utility realized by receptacles of this type is offset, somewhat, by the danger in thepresence of an electrically charged contact located within the blade receiving slots of the receptacle immediately beneath the frontface thereof. A child led by his explorative curiosity can easily electrocute himself by inserting a metallic object, such as a hairpin or nailfile, into the slots in the front face of the receptacle. 7

Several attempts have been made to develop a receptacle that is tamper-proof, at least with regard to young children: see, e.g. U.S. Pats. Nos. 2,735906; 2,770,786; 2,826,652; and 3,238,492. While the earlier devices have in part provided a safer receptacle, the resulting receptacles are not entirely satisfactory from a safety standpoint and also have the disadvantage of being relatively complex in nature. Some of them are provided with spring biased, slidable plates normally overlying the openings of both blade receiving slots, which require insertion of blades into both slots before opening sufficiently to expose the live contacts, thereby preventing entry of a single foreign object into the prong receiving slot, but opening if a foreign object is inserted into both slots. Other devices are provided with relatively intricate assemblies adapted to prevent the engagement of a foreign object with a current carrying contact within the receptacle. Therefore, because of the increased difficulty in the fabrication, assembly, maintenance and use of these earlier type devices, their cost have increased relative to conventional types of convenience receptacles, and their effectiveness is not altogether satisfactory, thereby their acceptance and use on a wide scale basis has not developed.

SUMMARY OF THE INVENTION The present invention, however, overcomes the cost and complexity difficulties of the earlier devices and provides a grounded, electrical receptacle that is essen-- tially tamper proof. Its simplicity of design and construction renders it favorably comparable to conventional types of receptacles. Within the receptacle body at least one of the electrical contact elements engaged by the grounding prongis movable andso positioned that insertion of the grounding prong on the plug urges the movable contact into engagement with a fixed contact connected to the power supply terminal completing the circuit. In the illustrated embodiment the mechanical contacts are positioned inside the receptacle body and the movable electrical contact is so arranged with relation to a tapered grounding prong that a complete insertion of the prong into its slot is required to urge the movable portion into contact with the fixed contact connected to the power supply terminal. Also, when the tapered grounding prong is fully seated, an exposed bead on the distal end thereof engages a grounding bridge that connects the prong to ground through the grounding wire terminal. Finally, to prevent an electrical shock that might result from insertion of a metallic object into the receptacles grounding prong receiving slot and the resulting engagement with the contact connected to the power supply terminal, an insulated covering is provided on the exposed surfaces of the movable contacts adjacent the path of the grounding prong within the ground prong receiving slot.

In a receptacle, constructed in accordance with this invention, therefore, there are initially no live contacts carrying an electrical current that could be conducted by a foreign object engaged therewith, and it is necessary to insert an attachment plug having a ground prong thereon in order to activate the electrical contacts therein. Therefore, the only way a young child might receive a shock from a receptacle, as described herein, is to insert an object of a shape and size similar to the ground prong in the grounding prong slot and simultaneously insert a second object into the electrical blade receiving slot connected to the power supply terminal. The understanding and manual dexterity required for such a combination of acts is considered to be beyond the ability of a child too young to appreciate the dangers of electrical receptacles.

It is therefore an object of this invention to provide a safety electrical receptacle in which the circuit carrying the electrical power input to the blade contacts is normally open and not completed until aproper plug or cap has been fully seated.

It is still another object of this invention to provide an electrical receptacle havinga grounding contact in addition to the normally provided electrical contact, the power input circuit thereof being normally open and requiring insertion of the ground prong to close the circuit.

Yet another object of this invention is to provide a grounding type receptacle that is substantially tamperproof.

Some of the objects of the invention having been stated, other objects will appear as the description proceeds, when taken in connection with the accompanying drawings, in which:

FIG. 1 is a plan view of an electrical receptacle of the type intended for the practice of this invention;

FIG. 2 is an elevation view of the receptacle illustrated in FIG. 1;

FIG. 3 is a view of the receptacle illustrated in FIG. 1 except looking from the bottom;

FIG. 4'is a sectional view with parts broken away taken substantially along lines 4-4 in FIG. 2 with the associated plug removed;

FIG. 5 is a sectional view similar to FIG. 4 except illustrating the plug in place;

FIG. 6 is a sectional view of the receptacle taken substantially along line 5-5 in FIG. 1 with the associated plug removed;

FIG. 7 is a sectional view similar to FIG. 6, except illustrating the plug in place; and

FIG. 8 is an elevation view of an attachment plug adapted for use with the receptacle illustrated in FIGS. 1-7, illustrating the ground prong constructed in accordance with one preferred embodiment of the present invention.

The embodiment of this invention as illustrated in the drawings relates to a receptacle contemplated for use with a specially adapted grounding plug. It should be understood, however, that the invention can also be practiced with a plug having a conventional grounding prong as will be hereinafter described. The substance of the invention lies in a switch means positioned within the receptacle body that is responsive to the insertion of a ground prong, which closes the circuit between the blade receiving contacts and a power supply terminal upon insertion therein.

Turning now to the drawings, FIGS. l-3 illustrate a duplex grounded receptacle, identified generally by the reference character 10, which, from its outer configuration appears to resemble a conventional receptacle, however, is interiorly constructed in accordance with the present invention. It should be recognized, however, that the present invention is not limited to a receptacle of the illustratedouter configuration, its use herein being merely for descriptive purposes. Receptacle comprises a body 20 comprising top member or cap 26 and bottom member or base 28, both parts preferably formed from an insulating material or nonconductor such as molded plastic. Mounting bridge 14 is suitably attached to base 28 and includes a pair of mounting ears 13, one of which protrudes outwardly from each end of base 28 and a grounding strip 14a connecting the two ears 13, extending along the lower exposed surface of base 28, and including a pair of ground prong receiving openings 19.

The illustrated embodiment of receptacle 10 comprises two

separate receptacles

22a and 22b in cap 26, each of which include side-by-

side slots

23 and 24 for receiving the electrical blades 25 of a grounding type attachment plug 11, see FIG. 8. A third opening or slot 18 in each of the

receptacles

22a and 22b receives the grounding prong of attachment plug 11. A contact bead 12 on the terminal end of prong 15 snaps into one of openings 19 and thus electrically engages ground strip 140, whereby the ground wire of plug 11 is connected to ground when the plug is fully seated within the terminal. Terminals 17 extend through suitable openings in the side of base 28 to connect a suitable power supply not shown) with contact elements within receptacle 10 to be hereinafter described.

Because the mechanical safety features of each side of the receptacle are substantially the same, one side of receptacle 10 will be described in detail with reference being made only to differences between the two sides.

Referring now to FIG. 4, a first, fixed electrical contact 30 is disposed within a cavity C in base 28 and positioned immediately beneath one of

openings

23, 24, in cap 26. A first resilient connecting strip 31 having a movable contact 32 at the free end thereof is integrally attached to contact 30 and in its normal position extends into the cavity C to a point adjacent the path of ground-prong 15 through passageway 18 in the receptacle. A second connecting strip 37, electrically engaging terminal 17a, includes an upper loop forming a second contact 36 disposed at a position slightly spaced from the normal position of movable contact 32. Fixed contact 36 and movable contact 32 essentially form a switch means connecting terminal 170 and first fixed contact 30.

The second connecting strip 37 is positioned against the side wall of base 28 and electrically engages 17a as well as 17a, extending into the lower cavity C in base 28. The lower end of connecting strip 37 terminates in a lower loop 36a at a position slightly spaced from the contact 32a, which in turn is integrally dependent from lower fixed contact 300.

Turning now to a description of the operation of movable contact 32, (see FIGS. 4 and 5), a leaf spring 33, if desired, may be suitably attached to an upstanding wall W in cavity C to resiliently support movable contact 32 and maintain it at a desired distance from fixed contact 36. It is apparent that spring 33 might be eliminated if strip 31 were sufficiently resilient to main tain contact 32 in the desired position after repeated use. However, strip 31, as well as the

other contact elements

30 and 37 are generally formed from a conductive material such as copper and therefore may not be sufficiently resilient in themselves. Leaf spring 33 therefore provides the necessary resiliency to maintain movable contact 32 in its proper spatial relation to fixed contact 36 after repeated usage.

Additionally, an insulative coating 38, covering leaf spring 33, is applied to the side of contact 32 opposite fixed contact 36 to shield movable contact 32 and leaf spring 33, preventing accidental current flow even if a foreign object be inserted into grounding slot 18 and manipulated to close

contacts

32 and 36.

The mechanical safety features of the other side of receptacle 10 are identical to the aforedescribed elements, and therefore no further description of the interior of base 28 is deemed necessary for an understanding of the invention.

An attachment plug 11 adapted for use with the receptacle illustrated in FIGS. 1-7 is shown in FIG. 8. A pair of electrical blades 25, depending from the plug cap 11a, is insertable into

slots

23 and 24 of one of the

receptacles

22a, 22b and engage the electrical contacts 30 therein. A grounding prong 15 also depends from cap 11a and comprises a cylindrical core 15a surrounded by a tapered insulating jacket 27 (FIG. 7) and terminating in an exposed bead 12 at the free end thereof. With the exception of the configuration of grounding prong 15, attachment plug 11 is of a type in common use and, therefore, requires no additional description. The connection between grounding prong l5 and mounting (grounding) bridge 14 is effected when attachment plug 11 is fully seated within one of the mating receptacles, thereby snapping exposed bead 12 into engagement with the walls of aperture 19 in ground strip 14.

In the operation of the above described receptacle, the current conducting means forming the circuit between terminals 17 and electrical contact 30 is normally held open by the switch means comprising

contacts

32 and 36, and the safety features are enhanced by the use of a specially shaped ground prong to close the circuit. See FIGS. 4 and 6. Foreign objects inserted into

slot

23 or 24 of the receptacle or into both slots simultaneously do not close the circuit and therefore minimize the risk of producing an electrical shock. In order to complete the circuit from the power supply to electrical contact elements 30, grounding prong 15, provided with a tapered insulated jacket 27, must be fully seated within grounding slot 18, whereupon mova ble contacts 32 are urged outwardly and into engagement with their respective fixed contacts 36, as illustrated in FIGS. 5 and 7, closing the circuit to contact elements 30. With plug 11 partially inserted, the electrical blades 25 would engage contacts 30, however, would not present a danger of shock, because the circuit is not completed until ground prong 15 is fully seated. Furthermore, a plug without a suitable adapted grounding prong will not engage the movable and fixed contacts, and therefore, will not complete the electrical circuit to electrical contact elements 30.

It is possible to adapt existing plugs to operate with receptacles of the type herein described by providing the ground prong thereof with an insulating jacket and exposed bead, manufactured in a manner which, when slipped over the existing prong, would fit tightly thereover and be extremely difficult to remove.

However, a conventional plug may be used in the practice of this invention by adjusting the thickness of the insulative coating 38 on movable contacts 32 (not shown) such that insertion of an existing grounding prong will cause the movable contact 32 to engage fixed contact 36, thereby completing the electrical circuit between the power supply terminal 17 and electrical contacts 30. To prevent activation of the electrical circuit prematurely, the position of the movable contacts relative to that of the grounding prong, when the latter is inserted into the body of receptacle 10, can be regulated so that the circuit will not be closed until the grounding prong is fully seated therein. When a conventional plug is used, the grounding connection between the grounding prong and grounding terminal 16 (FIG. 7) is accomplished in a conventional manner such as by running the grounding strip 19 through the upper regions of the receptacle, thereby eliminating the requirement of the exposed bead 12 illustrated in the drawings and discussed hereinbefore.

In the drawings and specification, there have been set forth preferred embodiments of the invention, and although specific terms are employed, they are used in a generic and descriptive sense only and not for purposes of limitation, the scope of the invention being defined in the following claims.

Iclaim:

1. A safety electrical receptacle comprising:

a. a housing having exterior walls defining a cavity therein, and a grounding strip along the lower surface thereof, said grounding strip including an opening therein;

b. a current supplying terminal extending through the wall of said housing and adapted to be connected to an external power source;

c. a first electrical contact spatially positioned from said-terminal within said cavity, said first contact adapted to receive one of the blades of a connector plug;

d. a switch means interconnecting said terminal and said first contact and normally maintaining an open circuit therebetween, said switch means being actuable to close the circuit therebetween; and

e. a ground prong receiving passageway extending through said cavity, spaced from said first electrical contact and adapted to receive the ground prong of said connector plug, said ground prong comprising a metallic core having an enlarged bead on the lower end thereof and an insulating, tapered acket around the remainder of the core,

said insulating jacket in its seated position engaging said switch means to close the circuit between said terminal and said first contact, the opening in said grounding strip being in the path of said ground prong on said connector plug, said enlarged bead in its seated position snapping into the opening in said grounding strip and making electrical connection therewith.

2. The receptacle according to claim 1 wherein each of said movable contacts is normally positioned adjacent the path of said ground prong through said receptacle.

3. The receptacle according to claim 2 wherein said movable contact is insulated on the side facing the path of said ground prong.

4. The receptacle according to claim 2 wherein said movable contact comprises a resilient conductive strip attached at one end to said first electrical contact.

5. The receptacle according to claim 2 and further including a leaf spring connected at one end to said first electrical contact, the other end being connected with the free end of said movable contact and normally biasing said free end away from said fixed contact.

Claims

1. A safety electrical receptacle comprising: a. a housing having exterior walls defining a cavity therein, and a grounding strip along the lower surface thereof, said grounding strip including an opening therein; b. a current supplying terminal extending through the wall of said housing and adapted to be connected to an external power source; c. a first electrical contact spatially positioned from said terminal within said cavity, said first contact adapted to receive one of the blades of a connector plug; d. a switch means interconnecting said terminal and said first contact and normally maintaining an open circuit therebetween, said switch means being actuable to close the circuit therebetween; and e. a ground prong receiving passageway extending through said cavity, spaced from said first electrical contact and adapted to receive the ground prong of said connector plug, said ground prong comprising a metallic core having an enlarged bead on the lower end thereof and an insulating, tapered jacket around the remainder of the core, said insulating jacket in its seated position engaging said switch means to close the circuit between said terminal and said first contact, the opening in said grounding strip being in the path of said ground prong on said connector plug, said enlarged bead in its seated position snapping into the opening in said grounding strip and making electrical connection therewith.