US3531757A - Grounded plug - Google Patents

Description

M. ALDEN Sept. 29, 1970 GROUNDED PLUG Filed May 15. 1968 M /LTON ALDEN INVENTOR.

United States Patent O trust Filed May 15, 1968, Ser. No. 729,365 Int. Cl. H01r 13/08, 13/42 U.S. Cl. 339-14 2 Claims ABSTRACT F THE DISCLOSURE In general, this invention relates to an electrical plug adapted to be used with a convenience outlet and having, in addition to the usual two prongs, a third prong for connection to a grounding outlet. More specifically, the third prong is removable in those instances where it is not needed or desirable.

BACKGROUND OF THE INVENTION It has long been recognized that it is desirable to provide a means for grounding certain electrical appliances during use. An ungrounded motor driven hand drill, for instance, could electrocute the user, if a high voltage were to appear on one of the electrical conduits, as sometimes happens if a power line transformer is short-circuited during a storm. For that reason, it has been common practice to connect the frame of the appliance to a third wire in the power cord and to connect that third wire to a third prong on the plug at the end of the cord. Unfortunately, many electrical convenience outlets are not provided with a third opening to fit the grounding prong, yet the user of the appliance may wish to connect the appliance despite the recognized danger in doing so. An adapter plug may be inserted between the three-pronged plug and the twoopening convenience outlet in order to permit such use. Another popular method of solving the problem is to mount the grounding plug on a hinge on the plug so that, if it is not to be used, it may be swung to an inoperative position; this method is not entirely satisfactory because of the poor electrical conducting properties of a mechanical hinge. This inadequacy will be appreciated still more when it is recognized that the grounding prong could be entirely inoperative for years (because of wear or corrosion in the hinge) without the owner of the appliance realizing it, yet not be available to save him when an electrical emergency occurs. These and other difficulties experienced with the prior art devices have been obviated in a novel manner by the present invention.

It is, therefore, an outstanding object of the invention to provide an electrical plug which has a grounding prong which may be easily removed.

Another object of this invention is the provision of an electrical plug which can be easily and quickly converted from two-prong to three-prong and vice versa.

A further object of the present invention is the provision of a convertible grounding plug which is simple in construction, inexpensive to manufacture, and which is capable of a long life of useful service with a minimum of maintenance.

It is another object of the instant invention to provide an electrical plug with a grounding prong which can be deactivated, yet which is not subject to becoming electrically inoperative for grounding purposes because of mechanical wear or chemical attack.

A still further object of the invention is the provision of an electrical plug having a grounding prong which can be easily replaced with a pig-tail type grounding device.

3,53l,757 Patented Sept. 29, 1970 ICC With these and other objects in view, as will be apparent to those skilled in the art, the invention resides in the combination of parts set forth in the specification and covered by the claims appended hereto.

SUMMARY OF THE INVENTION In general, the present invention consists of an electrical plug having a body formed of insulating material, a grounding pin, a passage in the body adapted to receive the pin on occasion, and means located in the passage providing excellent electrical conductivity with the pin when it is inserted in the passage.

BRIEF DESCRIPTION OF THE DRAWINGS The character of the invention, however, may be best understood by reference to one of its structural forms, as illustrated by the accompanying drawings, in which:

FIG. 1 is a perspective view with portions broken away of an electrical plug embodying the principles of the present invention,

PIG. 2 is a sectional view of the plug taken on the line II-II of FIG. 1,

FIG. 3 is a sectional view of the plug taken on the line Ill-III of FIG. 2,

FIG. 4 is a sectional view of the plug taken on the line IV--IV of FIG. 2, and

FIG. 5 is a perspective view of a grounding attachment for use with the plug.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring first to FIG. l, wherein are best shown the general features of the invention, the electrical plug, indicated generally by thereference numeral 10, is shown as having a main body 11 from one side of which extends a neck 12. Into the neck extends three strands or wires, including two normal electrical wires 13 and 14 and a ground wire 15. These wires are adapted to be connected at their other ends to the electrical binding posts in an electrical appliance (not shown) and, in the case of the wire 15, to the frame of the appliance.

From the other side of the body 11 extend two conventional prongs 16 and 17 connected, respectively, to the wires 13 and 14. Also extending from the said other side of the body is a grounding pin or prong 18 which is connected, in a manner which will be described hereinafter, to the wire 15. This prong is of ogive form at its outer end and at its inner end is provided with a generous groove 19.

lntegrally -molded into the main body 11 is a clip 21 preferably formed of copper. As is evident in FIG. 1, the clip is formed from a strip of metal stock into a generally figure-8 shaped element. The free ends of the strip fail to me'et by an appreciable amount to leave a gap 22. Referring to FIG. 3, the bight loop 23 is provided at its upper portion with two opposed inwardly-directed indentations 24 and 25 which engage and clamp the wire 15 whose insulation 26 has been stripped back for that purpose; solder, not shown, may be used between the clip and the wire to assure a complete electrical connection.

As shown in FIG. 4, the loop 27 defined by the free ends of the clip 21 is provided at its lower portion with two opposed, inwardly-directed indentations 28 and 29 which snap into the groove 19 of the grounding prong 18.

As can be seen in FIG. 2, the material of the main body 11 overlies the upper end of the clip 21, but an access opening 31 extends from the interior of the loop 27 through the body. The prong 18 passes through this opening.

The use and operation of the invention will now be readily understood in view of the above description. As has been stated, the wires 13 and 14 are normally connected to the electrical elements of the electrical appliance,

while the wire 15 is connected to its frame. The prongs 16 and 17 are normally inserted in a convenience outlet. The prong 18 is inserted into a third opening of the convenience outlet and lprovides, therefore, suitable grounding for the appliance. The electrical connection between the prong 18 and the clip 21 is excellent because the indentations 28 and 29 press tightly into the groove 19 in the prong. Also, there is broad electrical contact between the cylindrical surface of the prong and the inner surfaces of the clip. This inward pressure is brought about not only because of the natural resilience of the clip, but also because the clip is almost entirely surrounded by the elastomer material from which the main body is formed. The electrical transmission characteristics of the engagement between the indentations 28 and 29 and the surface of the groove 19 are enhanced by the tendency of the prong 18 to rotate somewhat during use; this polishes the surfaces and removes any accumulation of dirt, oxide, or chemical, which substances would otherwise remain between the contacting surfaces and tend to insulate them from one another. The only access to these contacting surfaces is through the small opening 31 in the main body and this is normally occupied by the prong 18. It is interesting to note, particularly referring to FIGS. 2 and 4, that a substantial space exists below the lower end of the prong 18; this provides a place for dirt and the like to fall after being freed from the contacting surfaces of the clip and plug.

Now, on those occasions when the convenience outlet is not provided with the special grounding opening to receive the prong 18, it is a simple matter to grasp the prong 18 and remove it from the plug. In the same way, the prong can be returned to the plug quickly and without diiculty.

If the convenience outlet is not provided with a grounding opening and yet the user feels that grounding is necessary, the element 32 shown in FIG. 5 may be used. This element is provided with a pin 33 having a groove 34 adapted to be inserted into the plug through the opening 31 for engagement Iby the clip 21, particularly for engagement of the indentations 28 and 29 with the groove 34. In addiv tion, the element has a connector strip 35 which is mechanically and electrically connected at one end to the upper end of the pin 33, while at the other end it is provided with a slot 36. The slot engages the center fastening screw of the convenience outlet to provide good grounding through the outlet box. The intermediate portion of the strip 35 is formed into a loop to provide compensation for the distance between the plug and the fastening screw for the convenience outlet and to provide resilience to bias 4. the slot constantly into electrical engagement with the screw, even if the screw is loose.

It is obvious that minor changes may be made in the form and construction of the invention without departing from the material spirit thereof. It is not, however, desired to confine the invention to the exact form herein shown and described, but it is desired to include all such as properly come within the scope claimed.

The invention having been thus described, what is claimed as new and desired to secure by Letters Patent is: 1. A plug having an electrical ground, comprising:

(a) a main body molded of elastomeric material;

(b) a three wire electric cab-le xedly secured within said main body;

(c) two prongs fxedly embedded within said main body one wire of said electric cable being connected to each of said prongs;

(d) a U-shaped resilient metal clip connected to the third wire of said electric cable and resiliently mounted within said main body in such a manner that the ends of said U-shaped metal clip are capable of lateral displacement within said main body; and

(e) an elongated unitary grounding prong which is removably connected to said clip in such a manner that the ends of said clip are laterally displaced within said main body and resiliently and frictionally engage said grounding prong.

2. A plug having an electrical ground as recited in claim 1, wherein the grounding prong includes a pin for insertion in the clip and a resilient strip adapted to connect the pin to a fastening screw of a convenience outlet.

References Cited UNITED STATES PATENTS 1,808,335 6/1931 Auero 339-258 2,266,530 12/1941 Andren 339-258 XR 3,034,083 5/ 1962 Traher 339--14 FOREIGN PATENTS 1,228,931 3/1960 France.

117,771 12/ 1946 Sweden.

MARVIN A. CHAMPION, Primary Examiner P. A. CLIFFORD, Assistant Examiner U.S. Cl. X.R. 339--31

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