Three prong plug with ground safety cutout

A three-prong electrical plug includes a replaceable ground prong and circuitry inside the plug to preclude its functioning without the ground prong.

This invention relates to electric three-prong connectors, and more specifically, to a three-prong connector that will not transmit electricity if the ground prong is removed or damaged.

BACKGROUND OF THE INVENTION

The use of three-prong plug electrical connectors for appliances, extension cords, electric tools, etc. has become widespread. The use of three prongs, hot, neutral and ground, makes the operation of any electric appliance, tool, etc. safer. If there is a short, the ground wire provides a safe path for current.

The standards for a three-prong plug include, hot and common or neutral prongs that are elongate and flat (usually sheet metal, backfolded at the distal end of the prong). In contrast, the ground prong is cylindrical in shape, i.e., usually a piece of sheet metal bent to form a hollow cylindrical shape or “U” shape with a rounded distal end. In a typical three-prong plug, the hot and neutral prongs are somewhat ductile being flat and may be bent from side to side when being pulled from a socket and then manually straightened again. However, the hollow cylindrical or U shape ground prong has normally been heavily worked by being bent into its hollow shape and has become work hardened or brittle, even before it is put in use. Also, it is not ductile from side to side as are the hot and common prongs. Further, the ground prong being made from sheet stock, a tongue or unbent central portion that extends from the hollow cylinder into the plug housing becomes a weak point in the ground prong design, if it is repeatedly bent (as are the hot and common prongs) when being pulled from an electrical socket.

The differences in ductility and brittleness between the hot and neutral prongs and the ground prong, results in differences in their fracture rates on the same three prong plug. In use, the brittle stiff ground prong often severely bends or fractures at its base with the rubber insulation cover of the plug. If thus deformed, an operator may then break off the ground prong. The problem with conventional three-prong plugs is that the plug will continue to work as a two-prong plug, although it will not provide the safety of a ground connection in case of a short.

Many municipal codes require or mandate discarding or non-use of electrical plugs or extension cords lacking a useable ground prong. However, in use, especially at construction sites, workmen encountering a damaged ground prong on such a connector will break off the ground prong and use the connector in an ungrounded condition, in violation of such codes.

In an effort to overcome the deficiencies of a standard three-prong plug, U.S. Pat. No. 5,622,509 provides a three-prong electrical connector having a flexible resilient grounding prong. However, the spiral wound grounding prong may be too resilient for its application as disclosed in the patent.

U.S. Pat. No. 3,914,565 discloses a three-prong plug invented in the 1970's when three-prong sockets were new in use. The solid ground prong is biased in a non-working position and must be moved into the body to close a pair of switches to provide a usable plug. The device is more complex than necessary and the added components provide more chance for failure in use. This patent depends upon the ground prong bottoming out in the socket which is not possible in all socket designs.

A need has developed for a simple three-prong electrical connector (plug) that provides the added safety feature of not functioning when the ground prong is disabled. Additionally, a need has developed for a three-prong male connector or plug that has the provision of easy repairability or replacement of the ground prong should the same become disabled.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention, generally stated, to provide a new and improved three-prong male electrical connection plug. Another object of the present invention is the provision of a three-prong male electrical connector plug that ceases to function if the ground prong should become disabled.

Further, the ground prong is designed to break away or dislocate from its socket, prior to the breaking point of the prong itself simultaneously rendering the plug usable in an unsafe condition.

A further object of the present invention is the provision of an easily replaceable ground prong in a three-prong male electrical connector.

The invention is directed to a three-prong grounded electrical connector for operatively engaging a three-conductor electrical cord. The connector comprises a body of electrically-insulated materials including a first electrically-conductive lead secured in the body and extending therefrom, a second electrically-conductive lead secured in the body and extending therefrom, and an electrically conductive grounding prong selectively releasably secured in the body and extending therefrom. A switch in the body is operatively connectable to a hot conductor of the three conductor cord. A spring between the grounding prong in its operative position and the switch maintain the switch in a closed position. The switch is biased in an open position when the prong is released from securement in the housing.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring toFIG. 1, a three-prong male electrical connector or plug, generally indicated at10, and constructed in accordance with the present invention, includes an insulated housing, generally indicated at11, preferably made of molded rubber, plastic or other non-conductive material, and further includes sticking outwardly therefrom on the distal end16thereof, a hot electrical prong12, a neutral or common prong13, and a ground prong14. At the rear of the housing11, a three wire electrical cord, generally indicated at15, extends therefrom.

Referring toFIG. 2, the ground prong14is shown exploded outwardly from its socket type receptacle, generally indicated at20, to be described in more detail below. Ground prong14is selectably releasably retained in its socket receptacle20for two purposes. The first is so that it may be replaced if it becomes damaged, as often happens with electrical connectors or plugs. The second is that the rear of the ground prong14includes a spring31for biasing a contact or switch (26,27) in the preferred embodiment, in the wiring of the hot prong12, such that the entire plug will not conduct electricity if the ground prong is disabled.

Referring toFIGS. 3,4and5, diagrams of the internal parts of the male three-prong connector or plug10are shown. The inside of the housing11receives at its back end, the hot, common and ground conductors22,23and24, respectively, that extend from the three conductor cable15. While hot prong12is fixedly embedded in the molded housing11, a pair of electrical contacts,26,27are retained on the ends of prong12and conductor22, respectively, so as to provide current from the hot conductor22to the hot prong12when the contacts26,27are closed. In this embodiment, contact27is stationary in the housing11while the other of the contacts26is mounted on an arm28connected at a bendable bight portion29to the interior end of positive prong12. With the arm28biased in an open direction (shown by the arrow inFIGS. 3 and 4) the contacts26and27would tend to be open if not for a spring31, made of insulative material or at least insulated from contact26. While an internal end of spring31is in biased contact with the back end of contact26, an outward end of spring31is received on the inner end of ground prong14where, if not made of insulative material, spring31is insulated from the remainder of ground prong14. The spring may also be affixed at its end with contact26and be loosely insulatively received in a pocket at the ball end14aof ground prong14.

In one aspect of the present invention, the preferably solid ground prong14, at its internal expanded or ball end14ais received, in this preferred embodiment, in a ball shape socket32in housing11that is conductively connected to the ground lead24. Outwardly adjacent the ball shape socket32is a conical hollow area, generally indicated at33which has an annular shaped resilient retaining ring34mounted thereacross. While the preferred embodiment is ball shaped at its inner end14a, it will be understood that other shapes that provide a known resistance to their removal may be utilized within the scope of the invention. The inner end of ball shaped socket32where it joins conical area33is of a constricted diameter that retains the ball end14aof prong14in its mounted position, up to a point. The size of the constriction may be varied to assure that a predetermined minimum force is necessary to remove the prong from the socket.

Referring toFIG. 5, the purpose of the resilient annular retaining ring33in the preferred embodiment is shown in more detail. When the ground prong14is dislodged from the connective conducting socket32, either purposefully or by accident, it extends outwardly from the socket to the conical area33adjacent the front wall11aof the housing11.

The resilient annular retaining ring33deforms outwardly a sufficient amount to restrain the ball end14aof ground prong14from fully exiting the front end of the plug housing11. With the ground prong14pulled out of its socket32, the spring31releases its bias against contact26. The bias built in the bight portion29and arm28of contact26opens the contacts26and27stopping current flow from hot lead22into hot prong12, thus rendering the connector temporarily inoperable. With the ground prong being solid, it is difficult for a user to cut the prong in two in an attempt to provide operability to the connector. Generally less force is necessary to pull the ground prong out through the retaining ring34than through the socket constricted area.

However, spare or replacement ground prongs14are available to replace the damaged ground prong and may be inserted through the resilient annular ring and conical section33into the socket32at which time the spring31positioned in the inner end of the ball portion14aagain biases contact26against contact27to provide a workable three prong plug.

When the ground prong14is deformed such that it cannot be inserted into a conventional three-prong socket, the connector of the invention will not operate as a two prong connector, if the ground prong14is pulled out of its socket. However, identical spare ground prongs may be utilized similarly to bits in a drill. They may be stored away from the connector or, if consistent with UL policies and CPSC rules, a spare prong may be stored by removably embedding same in a slot11bin the top of the insulative housing11. When the ball end14aof the spare ground prong14is inserted in the socket32, the connector will again function properly and safely.

While one embodiment of the present invention has been shown and described, it will be apparent to those skilled in the art that many changes and modifications may be made without departing from the true spirit and scope of the present invention. It is the intent of the appended claims to cover all such changes and modifications which fall within the true spirit and scope of the invention.