US3786392A

US3786392A - Automatic retractable ground electrical connector

Info

Publication number: US3786392A
Application number: US00290506A
Authority: US
Inventors: Daniel J Mc
Original assignee: Individual
Current assignee: Individual
Priority date: 1972-09-20
Filing date: 1972-09-20
Publication date: 1974-01-15
Anticipated expiration: 1991-01-15

Abstract

A three prong electrical connector or plug having a spring biased grounding prong of sufficient strength to retain the ground prong extended for insertion into a three way electrical outlet and to allow the ground prong to retract when the plug is inserted into a two way electrical outlet. For plugs having a relatively short longitudinal dimension, the grounding prong is made of telescopic sections. A small conductive strip is provided to be secured to the face plate screw of a two way electrical outlet so that the ground prong is grounded even in the retracted position.

Description

ite States McDaniel Jan. 15, 1974 AUTOMATIC RETRACTABLE GROUND ELECTRICAL CONNECTOR [76] Inventor: Johnny B. McDaniel, 4210 Stanby Ct., Alexandria, Va. 22312 [22] Filed: Sept. 20, 1972 [21] App]. No.: 290,506

[52] US. Cl. 339/14 P, 339/31 R [51] Int. Cl ..1H01r 3/06 [58] Field of Search 339/14 R, 14 P, 14 RP, 339/31 R, 31 B, 31 L, 31 M, 31 T, 32 R, 32 M, 33

[56] References Cited UNITED STATES PATENTS 3,739,317 6/1973 Wise 339/14 R 3,308,415 3/1967 Cramer et a1. 339/14 R 3,685,000 8/1972 Robbins... 339/14 P 3,531,757 9/1970 Alden 339/14 P FOREIGN PATENTS OR APPLICATIONS 902,775 8/1962 Great Britain 339/31 R Primary Examiner-Marvin A. Champion Assistant Examiner-Robert A. I-lafer AtI0rneyMorris Fidelman et al.

[5 7] ABSTRACT A three prong electrical connector or plug having a spring biased grounding prong of sufficient strength to retain the ground prong extended for insertion into a three way electrical outlet and to allow the ground prong to retract when the plug is inserted into a two way electrical outlet. For plugs having a relatively short longitudinal dimension, the grounding prong is made of telescopic sections. A small conductive strip is provided to be secured to the face plate screw of a two way electrical outlet so that the ground prong is grounded even in the retracted position.

13 Claims, 7 Drawing Figures WENTEWM 15 m4 44 I Iii FIG/6 AUTOMATIC RETRACTABLE GROUND ELECTRICAL CONNECTOR FIELD OF THE INVENTION This invention relates generally to a three prong electrical connector and more specifically to a three prong electrical connector having an automatic retractable ground plug.

DESCRIPTION OF THE PRIOR ART The National Safety Council records annually hundreds of electrical shock incidents and many fatal home/industrial electrocution accidents caused in whole or part by non-grounded electrical power tools and appliances. Additionally, a severe shock hazard exists when power tools and appliances are in use during an electrical storm; where an over-voltage or power line short-circuit may inadvertently charge the frame of the appliance with a potential lethal voltage.

Most modern appliances now feature an internal ground for the motor to the frame and the convenience outlet by the use of a third grounding cable contained in the power cord set. In older homes, offices or industrial facilities where the convenience outlets lack a proper ground opening and lug, the use of an adapter plug socket connector provides electrical poer to the appliance but may not afford any degree of ground protection. Some of the adapter wire plugs feature a green coded ground with a connector lug that may be connected beneath the central threaded screw that attaches the receptacle over plate to the convenience outlet. The National Safety Council points out that most people neglect to make the required connection even if provided because of the following reasons: lack of an available screwdriven in a hurry;" didnt understand what the wire was for; etc., etc.

All adapter plug-sockets exhibit a common troublesome problem for the user, that being, when connected between the appliance connector and the convenience outlet, the resulting combination tends to sag and pull away from the convenience outlet due to the weight or movement of the appliance cord set. This often results in an electrical OPEN as the male sabre pulls free of the connector with the appliance losing power or arcing and pitting occurring within the convenience outlet terminals. These and other difficulties may be experienced with prior art devices but are now made obsolete by the novel design feature of this present invention.

The prior art is replete with examples of attempts to provide a three prong plug with a feature to allow the grounding plug to be removed for two wire outlets.

. Some have even provided locking mechanisms to manually move the prong into the body of the plug and lock it in either the retracted or the extended position. However, none of the plugs of the prior art provide a means to ground the three wire plug to a two wire terminal. Also without such additional means, the three wire plugs become essentially a two wire plug that is ungrounded, therefore the use of the appliance is unsafe.

SUMMARY OF THE INVENTION The present invention is a three wire plug having a spring loaded, automatically retractable ground. The grounding prong mechanically and electrically contacts a metal housing and slides therein. 'A positive spring action provides the required tension to allow the grounding prong'to be normally inserted into a three aperture outlet, and allows the prong to retract within the body for use in the older two aperture outlets. A piece of conductive metal is provided to establish a connection between the cover plate screw which is grounded and the face of the outlets so that the retracted electrical prong is grounded. For the low profile flatback or short plugs, the grounding prong may be composed of telescopic sections.

OBJECTS OF THE INVENTION An object of the present invention is to provide a foolproof electrical cord-set connector that automatically grounds, retracts and adapts to any convenient outlet without the troublesome burden of using a separate adapter plug-set and/or pigtailed ground wire extensions.

Another object of the invention is to provide an automatically retractable ground that is simple in construction, use and manufacturing techniques.

A further object of the invention is to provide an electrical ground prong which is redundantly connected to the ground wire.

Still another object is to provide an automatically retractable ground for the low profile flat-back or narrow plugs.

Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective sectional break-away side view of the male connector plug;

FIG. 2 is a sectional break away view of an alternate embodiment of the grounding prong and casing;

FIG. 3 is a cross-sectional view of a third embodiment of the grounding prong and casing;

FIG. 4 is a side view of the conductive strip for use in older two-hole receptacles;

FIG. 5 is a front view of the use of the conductive strip with the older two-hole receptacles;

FIG. 6 is a perspective sectional break-away side view of a telescopic retractable grounding prong in a low profile flatback male connector plug; and

FIG. 7 is a side view of a locking pin.

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1, which illustrates a preferred embodiment of the present automatic retractable ground electrical connector, shows a plug 10 and a three conductor electrical cord 12 attached thereto. Two of the electrical connectors of the cord 12 are electrically and mechanically connected to two male prongs l6 and 17. In the perspective cut away view, electrical connector 14 is shown connected to male prong 16 at point 18. The electrical cord, as well as the two male prongs and the retractable ground prong, are all housed in a body 20 made of suitable insulating material. The forming of the body 20 with the three male prongs electrically connected to the three electrical conductors of the cord 12 is well known in the art. For example, this may be done with mold injection machines or any similarly known device of the prior art.

The ground conductor 22 of electrical cord 12 is attached to ground prong casing 24 at the end thereof by soldering, for example. Inside casing 24 is the grounding prong 26. The grounding prong slides along the interior of casing 24 and makes mechanical and electrical contact thereto. The resilient spring 28 is attached to the rear of casing 24 and is electrically connected to ground conductor 22. The other end of spring 28 applies a force against the ground prong 26. Spring 28 may be attached to the enclosed end of prong 26. Thus a redundant electrical connection of the electrical conductor 22 to ground prong 26 is made through the easing 24 and the spring 28. Thus, if either one of the groundpaths should be broken, the other one will provide electrical continuity for an efficient and safe ground.

The grounding prong 26 of FIG. 1 is shown to be completely cylindrical with a tapered tip. Ground prong 26 in the fully extended position extends past the

other prongs

16 and 17 as required by the National Electrical Code. The length and strength of spring 28 is such that the grounding prong 26 will remain extended and will insert into a conventional three hole or apertured wall outlet. Upon the insertion of plug into the older two hole outlet, the grounding prong 26 will retract against the force of spring 28 back into the casing 24. The length of spring 28 is such that the rear end of grounding prong 26 at which the spring 28 is connected, will never leave the casing 24 and therefore the insulated body 20. The simplicity of the design of FIG. 1 and the minimum number of parts guarantees the versatility and high mechanical reliability of the retractable grounding plug. Also the use of minimum parts extends the useful life of the present plug. An aperture 27 is provided in grounding prong 26 to receive a locking pin 94. If spring 28 should break, grounding prong 26 can be locked in the fully extended position inserting tapered end 96 of locking pins 94 in aperture 27. The locking pin 94 is illustrated in FIG. 7, having a head portion 98 and a tapered end 96. The pin remains secured in the aperture 27 due to the tapered shape of end 96. The locking plug is made of nyon or plastic. As described above, the present invention insures grounding through the casing if the spring should break. If the shape of the connectors body does not have a major recess for the grounding prong as shown in FIG. 1, the head portion 98 of the locking pin 94 could be eliminated.

An alternate embodiment of the grounding plug and its casing is shown in FIG. 2. The casing 30 has two

longitudinal channels

32 and 34 diagonally across from each other. Within these channels slide

protrusions

36 and 38 of electrical ground prong 40. The ground prong 40 is prevented from leaving the casing 30 by a from shoulder 42. Simple manufacturing techniques are known for extruding the casing 30 with the two

channels

32 and 34 therein. Without the use of the shoulder 42, the ends of the channels may be crimped so as to prevent the

protrusions

36 and 38 from leaving the housing. As in the previous embodiment of FIG. 1, a spring 43 is provided which produces a positive resilient force against the grounding prong 40 for its use as described above. Also the spring provides a redundant electrical ground connection. The

channels

32 and 34 provide a guide for

protrusions

36 and 38 and prevent rotational movement of the grounding prong 40. As in the previous embodiment, an aperture 41 is provided in prong 40 to receive locking pin 94.

Another alternate embodiment of the ground prong and casing is shown in FIG. 3. Here the casing 44 is shown as having a from shoulder 46 extending radially therefrom. The grounding prong 48 has a rear retention shoulder 50 which slides along and makes electrical and mechanical contact with the casing 44. The retention collar 50 terminates or abuts in the fully extended position at the front shoulder 46 of casing 44. As in the other embodiments, a spring 52 exerts positive mechanical force against the rear retention shoulder 50 and provides redundant electrical contact.

As mentioned above, there is always a chance that the spring 52 may weaken from extended use before the rest of the plug, in which case, the electrical continuity between the ground electrical connector and the grounding prong is maintained through the casings. Thus a means must be provided to allow the prongs to be mechanically manipulated to stay in the extended position or be allowed to retract. FIG. 3 shows a hole or aperture 54 in the side of casing 44. If the spring 52 should break, the prong 48 could be mechanically pulled forward and held in that position while the nylon or plastic locking pin 94 could be inserted through slot 54 which would be located behind the rear retention shoulder 50 when the prong 48 is fully extended. Thus the shoulder 46 of casing 44 and the rear retention shoulder 50 of ground prong 48 would be abutting and held there by the locking pin 94 inserted into aperture 54.

The problem still remains of maintaining ground continuity between the plug 10 and the older two way wall outlet. To provide this continuity, the present invention includes an electrical conductor 56 as shown in FIG. 4. The conductor is shown as having a center section 58 and two raised

parallel sections

60 and 62. Center section 58 has a hole 59 for receiving an electrical outlet cover plate screw. The two raised

parallel sections

60 and 62 have

holes

61 and 63, respectively, for receiving the ends of the automatically retractable grounding prong of the present invention. The

holes

61 and 63 are smaller than the grounding prongs so as to assure maximum continuous electrical contact. Preferably, the diameter of

holes

61 and 63 should be approximately 2/3 of the diameter of the grounding prong.

Sections

58, 60 and 62 may all be in the same plane, depending on the contour of the electrical outlet and its face plate.

A conventional two socket electrical outlet is shown in FIG. 5 as having a face plate 64 retained to the outlet by screw 66. Theoutlet has two

sockets

68 and 70 having

female receiving apertures

72, 74 and 76 and 78, respectively. The electrical conductor 56 is retained by screw 66 through a hole or aperture 59. The two parallel raised

sections

60 and 62 of electrical conductor 56 rest on the face of

outlet

68 and 70 respectively. These two surfaces lie in the position at which the ground or third aperture would be on the newer conventional three apertured wall outlet or sockets. Since the electrical box itself is normally grounded and screw 66 is connected to the box, an electrical circuit is created to the ground through the screw and the electrical-conductor 56. Thus when an electrical plug or connector of the present invention, as illustrated in FIGS. 1-3, is applied to the older, two apertured electrical outlets, the grounding prong is retracted partially into its casing and maintains electrical contact to ground through the electrical conductor strip 56, screw 66 and the electrical outlet box. Thus even in the retracted position, the present invention provides an electrical circuit to ground and consequently the safe use of the appliance to the consumer.

Unlike the solution of grounding adapters of the prior art having an electrical wire which must be applied to the center screw each time a portable appliance or tool is used, the present invention provides a simple conductive strip which may be applied and left on all electrical outlets. Thus the consumer would not be faced with the bother of electrically connecting ground every time. As indicated above, it is this inconvenience which is the main cause of not grounding equipment which requires a ground and thus increases the liklihood of electrocution. Thus the present invention has provided a combination of a fully automatic, retractable ground and a conductive strip which may be permanently installed to all electrical outlets such that the retractable electrical connector of the present invention will provide and maintain ground for the portable equipment being used.

In many present day applications, the electrical plug or connector does not allow for the use of an extremely long body as shown in FIG. 1. Thus, for example, in electrical dryers and air conditioners, a flat or short plug is used as shown in FIG. 6. The three wire electrical conductor 82 is shown extending from the side of the low profile, short flat-back body 80. Besides the two normal male

electrical prongs

84 and 85, there is the automatically retractable grounding prong of the present invention. As before, the grounding wire is shown electrically connected to casing 86 and spring 88. Because of the size of the body 80, the grounding prong of the present invention must be made in at least two

telescopic sections

90 and 92. The ends of the telescopic sections are slightly enlarged so that the ends of section 90 are retained in section 92 and the end of section 92 is retained in casing 86. This allows for the extending and retracting of the sections to perform as described above. The resilient spring is connected to the smallest diameter telescopic section 90.

Upon insertion of the plug 80 into a normal three socket electrical outlet, the

telescopic sections

90 and 92 are inserted into the grounding aperture. Upon application of the plug 80 into a conventional two aperture outlet having the conductive grounding strip 56 attached thereto, telescopic section 90 retracts within telescopic section 92, which also retracts partially within the casing 86 while maintaining electrical continuity through the conductive strip 56. Thus the automatically retractable grounding prong as illustrated in FIGS. 1-3 is adapted for use in the shorter or flat-back plug of FIG. 6. As in the other embodiments, the grounding prong may have an aperture to receive the locking pin 94.

It should be noted that all of the embodiments of the present invention show the grounding prong snugly fitting within its casing. This feature prevents foreign matter, such as dirt or grease, from interfering with the motion of the ground prong as would be the case in many prior art devices. Thus the present invention provides an automatically retractable electrical connector with redundant ground connection which provides a guaranteed ground to a two or three aperture electrical outlet using the minimum number of moving mechanical parts and therefore providing a cheap and long-lasting electrical connector.

Although the invention has been described and illustrated in detail, it is to be clearly understood that the same is by way of illustration and example only and is not to be taken by way of limitation, the spirit and scope of this invention being limited only by the terms of the appended claims.

What is claimed:

1. A plug in combination with a three conductor electrical cord comprising:

a body;

two prongs securely embedded in said body and electrically connected to two of said conductors;

a conductive general cylindrical casing completely embedded in said body, electrically connected to the third conductor which is to be grounded, and having a longitudinal channel extending substantially the length of said casing;

a grounding prong having a protrusion extending radially from said grounding prong and adapted to slide within said channel, thereby preventing rotation of said grounding prong; a spring biasing means in said casing connected to one end of said ground prong and being of sufficient resilience to independently automatically maintain said grounding prong extended when said plug inserts into a three hole socket and automatically allowing said grounding prong to retract within said casing when said plug inserts into a two hole socket.

2. A plug as in claim 1 wherein said biasing means comprises a spring mechanically and electrically secured to the interior of said casing and the interior of said grounding prong so as to provide redundant electrical contact between said third conductor and said grounding prong.

3. A plug in combination with a three conductor electrical cord comprising:

a body;

a conductive general cylindrical casing completely embedded in said body, electrically connected to the third conductor which is to be grounded, and having one end exposed;

a grounding prong having a radial aperture and slidably engaging said casing and making electrical contact thereto;

a tapered locking pin adapted to be inserted and retained in said radial aperture to lock said grounding prong when extended; and

spring biasing means electrically and mechanically connecting the interior of said casing and said grounding prong so as to provide redundant electrical contact between said third conductor and said grounding prong and automatically maintaining said grounding prong extended when said plug inserts into a three hole socket and automatically allowing said grounding prong to retract within said casing when said plug inserts into a two hole socket said ground prong being freely slidable in said casing when said locking pin is not in use, said spring means exerting sufficient force to keep said ground prong extended upon entry into a three-hole electrical receptable.

4. A plug as in claim 3 wherein said casing and said body include superimposed radial apertures which are juxtapositioned to said grounding prongs radial aperture when said grounding prong is fully extended.

5. A plug as in claim 3 wherein said grounding prong comprises a plurality of cylindrical members of different diameters interconnected telescopically.

6. A plug as in claim 5 wherein the spring is electrically and mechanically connected to said cylindrical member of the smallest diameter.

7. An automatically retractable ground electrical connector system for connecting and grounding a three conductor cord to either a two or three female electrical receptacle, said system comprising:

a body of insulated material attached to said cord;

two fixed prongs secured in said body and electrically connected to two of said three conductors;

generally cylindrical conductive casing secured within said body and electrically connected to the remaining ground conductor of said three conductors;

a third prong slidably received in one end of said conductive casing and electrically connected to said conductive casing;

a spring secured mechanically and electrically to the other end of said conductive casing and to said third prong urging said third prong to extend from said body;

a generally rectangular conductive element, with an aperture which is adapted to receive a screw of the receptacles face plate, adapted to extend over part of the receptacle and abut said third prong when said prong is inserted in said receptacle thereby grounding said third prong;

said spring having sufficient resiliency to maintain said third prong extended when said prong is inserted in the ground aperture of a female electrical receptacle, said third prong being automatically retracted into said body when said third contact engages and remains in contact, by the urging of said spring, with said rectangular conductive element.

8. An automatically retractable ground electrical connector as in claim 7 wherein said casing includes a longitudinal channel extending substantially the length of said casing and said third prong includes a protrusion extending radially from said third prong and adapted to move within said channel, thereby preventing rotation of said third prong.

9. An automatically retractable ground electrical connector as in claim 7 wherein said third prong comprises a plurality of cylindrical members of different diameters inter-connected telescopically.

10. An automatically retractable ground electrical connector as in claim 9 wherein said spring is electrically and mechanically connected to said cylindrical member of the smallest diameter.

11. An automatically retractable ground electrical connector as in claim 7 wherein said rectangular conductive element includes a center portion and two end portions vertically displaced from said center portion.

12. An automatically retractable ground electrical connector as in claim 7 wherein said rectangular conductive element includes at least a second aperture adapted to receive said third prong.

13. An automatically retractable ground electrical connector as in claim 12 wherein said second apertures diameter is less than the diameter of said third prong.

Claims

1. A plug in combination with a three conductor electrical cord comprising: a body; two prongs securely embedded in said body and electrically connected to two of said conductors; a conductive general cylindrical casing completely embedded in said body, electrically connected to the third conductor which is to be grounded, and having a longitudinal channel extending substantially the length of said casing; a grounding prong having a protrusion extending radially from said grounding prong and adapted to slide within said channel, thereby preventing rotation of said grounding prong; a spring biasing means in said casing ''''connected to one end of said ground prong and being of sufficient resilience to independently'''' automatically maintain said grounding prong extended when said plug inserts into a three hole socket and automatically allowing said grounding prong to retract within said casing when said plug inserts into a two hole socket.

3. A plug in combination with a three conductor electrical cord comprising: a body; two prongs securely embedded in said body and electrically connected to two of said conductors; a conductive general cylindrical casing completely embedded in said body, electrically connected to the third conductor which is to be grounded, and having one end exposed; a grounding prong having a radial aperture and slidably engaging said casing and making electrIcal contact thereto; a tapered locking pin adapted to be inserted and retained in said radial aperture to lock said grounding prong when extended; and spring biasing means electrically and mechanically connecting the interior of said casing and said grounding prong so as to provide redundant electrical contact between said third conductor and said grounding prong and automatically maintaining said grounding prong extended when said plug inserts into a three hole socket and automatically allowing said grounding prong to retract within said casing when said plug inserts into a two hole socket said ground prong being freely slidable in said casing when said locking pin is not in use, said spring means exerting sufficient force to keep said ground prong extended upon entry into a three-hole electrical receptable.

4. A plug as in claim 3 wherein said casing and said body include superimposed radial apertures which are juxtapositioned to said grounding prong''s radial aperture when said grounding prong is fully extended.

7. An automatically retractable ground electrical connector system for connecting and grounding a three conductor cord to either a two or three female electrical receptacle, said system comprising: a body of insulated material attached to said cord; two fixed prongs secured in said body and electrically connected to two of said three conductors; a generally cylindrical conductive casing secured within said body and electrically connected to the remaining ground conductor of said three conductors; a third prong slidably received in one end of said conductive casing and electrically connected to said conductive casing; a spring secured mechanically and electrically to the other end of said conductive casing and to said third prong urging said third prong to extend from said body; a generally rectangular conductive element, with an aperture which is adapted to receive a screw of the receptacle''s face plate, adapted to extend over part of the receptacle and abut said third prong when said prong is inserted in said receptacle thereby grounding said third prong; said spring having sufficient resiliency to maintain said third prong extended when said prong is inserted in the ground aperture of a female electrical receptacle, said third prong being automatically retracted into said body when said third contact engages and remains in contact, by the urging of said spring, with said rectangular conductive element.

13. An automatically retractable ground electrical connector as in claim 12 wherein said second aperture''s diameter is less than the diameter of said third prong.