Dead-front high current female power contact

Abstract: A female power contact (9) which is energized only upon insertion of a male plug (5). The contact (9) includes a plunger (21) which is biased toward a position which blocks accidental finger insertion into the contact. The plunger (21) also contains sharp points on its outer edge to further prevent accidental finger insertion into the contact. However, insertion of the male plug (5) into the female power contact (9), against the spring (25) bias, causes the plunger (21) to depress the spring (25) in order to produce an electrical connection between the male plug (5) and female contact (9).

Description: FIELD OF THE INVENTION The invention relates in general to electrical connectors and more specifically to a female power contact with a safety feature which helps to prevent industry workers from electrocution. BACKGROUND OF THE INVENTION It is well-known that a high current electrical connection is very dangerous and may cause a person to be critically injured. Electrocution is a major concern for not only children and adults at home but also for many industrial workers. Due to the size of high current socket contacts in industrial plants, it is easy for a person to poke a finger or other objects into a socket opening and touch electrically-live metal components within the socket. There have been numerous efforts to overcome this problem as outlined in the following patents: U.S. Patent No. 5,113,045 Crofton U.S. Patent No. 5,069,632 Avitan U.S. Patent No. 5,147,988 Appleton U.S. Patent No. 5,256,076 Hamlin U.S. Patent No. 4,148,536 Petropoulos U.S. Patent No. 5,586,646 Bridgeman U.S. Patent No. 5,112,237 Yang U.S. Patent No. 5,095,182 Thompson U.S. Patent No. 4,652,067 Lutzenberg U.S. Patent No. 5,186,639 Comerci As discussed in greater detail below, the preponderance of prior art concentrates on enhancing safety at home and not at the workplace. Several prior art socket arrangements are disclosed which incorporate devices and structures for avoiding accidents at home but the prior art generally neglects the problem of protecting industrial workers from electrocution. US Patent No. 5,113,045, entitled Safety Outlet, describes a safety outlet which requires male prongs to force a pair of plungers into making contact with a pair of switches. The prongs are inserted into the outlet in order to depress the plungers which, in turn, closes the switches and initiates a supply of current to the prongs. The plungers are positioned in a manner by which the insertion of foreign objects will not exert enough pressure to depress the plungers. This is the safety feature of the outlet. US Patent No. 5,069,632, entitled Electrical Supply Safety Socket, describes a safety socket which is activated only when female socket outlets are forced into contact with energized components by insertion of a plug. Insertion of the plug activates a spring-biased switch which biases two armatures between open and closed positions. The armatures are articulated to a pivotally mounted support in order for them to be displaceable toward and away from each other. This prior art device also reduces the chance of electrocution by requiring two objects to be inserted in order to overcome both the spring-biased switch and the contact armatures. US Patent No. 5,147,988, entitled Switching Electrical Receptacle, describes a power receptacle having a housing with sliding contacts of cylindrical symmetry which can be manually engaged. The housing slides into and out of an electrical connection with female contacts in order to make or break a circuit. The female contacts are connected to load terminals. US Patent No. 5,256,076, entitled Safety Electrical Receptacle, describes a receptacle which does not allow current flow until switches are closed by an inserted plug. The plug depresses an operating lever which, in turn, creates a connection between movable and fixed contacts. According to one embodiment, the plugs contain special posts in order to activate the switches. In another embodiment, the grounding tine is used to close switches which help transmit electrical energy to output wiring. US Patent No. 4,148,536, entitled Safety Electrical Receptacle, describes a receptacle which only operates when its female contacts are energized after the insertion of prongs. The prongs push an insulative member in order to establish a connection between a contact arm and a power line connector. US Patent No. 5,586,646, entitled Vehicle Locking System, describes a sliding contact linear switch. A system is disclosed which uses an actuator plunger, shiftable between two positions to lock and unlock a vehicular door. US Patent No. 5,112,237, entitled Safety Plug Receptacle, describes a receptacle which requires the body of a male plug to depress its spring loaded pin in order to engage an internal switch. The switch turns on a LED to notify the user that a connection is made. This prior art device prevents the possibility of short circuiting wires. US Patent No. 5,095,182, entitled Shockproof Safety Outlet, describes a socket with two blade slots which prevents users from receiving shocks. The longer of the two blades is used to activate the supply current. US Patent No. 4,652,067, entitled Electrical Connector with an Internal Switch, describes an electrical connector whose plunger is operable by the body of a male contact during insertion. Depending on the presence or lack of presence of a plug, the internal switch moves the plunger to open and closed positions. US Patent No. 5,186,639, entitled Electrical Connector with Plug Detection Switch, describes the use of a switch mechanism to detect the presence of a fully inserted plug and then produces a supply current. CH 468 092 A, which is considered as the closest prior art, discloses a female contact for receiving and electrically connecting a male plug. The female contact is provided with an outer sleeve having an inner portion and an outer portion of a large diameter entry bore for receiving the male plug. A spring biased plunger is arranged within the sleeve, adapted to move in response to an inwardly directed force by the male plug from a first position for preventing an unauthorized access from the outer portion to the inner portion, to a second position for electrically connecting the male plug to the energized inner portion. It is the object of the invention to improve the safety of such a female contact. SUMMARY OF THE INVENTION The object is solved by the invention according to claim 1. Advantageous developments of the invention are defined in the dependent claims. The present invention is directed at a solution to the problem of protecting persons in industry who work with high current socket contacts from electrocution. As discussed above, due to the physical size of high current socket contacts, it is easy for a person to poke a finger into the front hole and touch electrically-live metal components. This is, of course, very dangerous and, according to the present invention, a socket contact is provided which significantly prevents this from happening. According to the invention, a female contact is provided for creating an electrical connection only upon insertion of a male plug. Insertion of a foreign object such as a finger will not produce a connection and thus there is no threat of electrocution. The female contact of the invention consists of two separate areas, one which is energized and one which is unenergized. Within the contact is a biased plunger. The plunger is biased to a first position for blocking fingers and other extraneous objects from entering the female contact. The plunger can be moved by the male plug, against the spring biasing, to a position which completes the electrical connection between the male plug and the female contact. BRIEF DESCRIPTION OF THE DRAWINGS Various embodiments of the invention are described below with reference to the accompanying drawings, in which Fig. 1 is a drawing of a male contact; Fig. 2 is a schematic illustration showing a first embodiment of the invention in which the thrust spring is uncompressed; Fig. 3 is a schematic illustration showing the embodiment of Fig. 2 in which the thrust spring is compressed; Fig. 4 is a schematic illustration showing a second embodiment of the invention in which the thrust spring is uncompressed; Fig. 5 is a schematic illustration showing the embodiment of Fig. 4 in which the thrust spring is compressed; and Fig. 6 is a drawing of an alternate male contact. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Figure 1 shows a male plug 1 which has a contact mating area, consisting of louver springs 3, a mating pin 5 and an insulated male contact tip 7 . Figure 2 shows a female socket 9 , according to a first embodiment of the invention, which contains a large diameter entry bore 11 , within an outer sleeve 13 , housing an electrically unenergized area 15 and an electrically energized area 17 , separated by an insulator 19 . The bore 11 houses a biased plunger 20 comprising a non-conductive plunger 21 which bars entry into the energized area 17 . The bore/spring area around the plunger 21 is sealed off by an O-ring 23 . The plunger 20 also contains a large thrust spring 25 to force the plunger 21 forward in the bore 11 thereby preventing accidental touching of the energized area 17 . The unenergized area 15 and the energized area 17 are electrically isolated and the spring 25 resists depression of the plunger 21 . Cable termination is achieved through a threaded bolt 27 although a crimp, solder barrel or flat blade may also be used. A dog leg lock 29 is used for retention of the male plug 1 via mating pin 5 . Upon insertion of the male plug 1 into the female socket 9 (Figure 3), physical contact is made between the male contact 7 and the insulated plunger 21 . The inward force applied by the male plug 1 depresses the thrust spring 25 which allows the insulated plunger 21 to recede into the bore 11 until the male plug 1 is fully mated and locked via a quarter-turn twist with the mating pin 5 fitting with the dog leg lock 29 . In this position, the conductive louver springs 3 of the contact mating area of plug 1 are connected with the energized area 17 and an electrical connection is produced. Figure 4 shows another embodiment of the female socket 9 . The second embodiment works in the same manner as the first embodiment with the following differences. Within the bore, a recessed conductive pin with a non-conductive tip 31 , connected to an insulated or uninsulated plunger cap 33 , is fitted with either single, double or multi-louver spring bands 35 , depending on the voltage applied. Use of louver spring bands 35 allows for a large current flow. The biased plunger 20 slides back and forth within the bore 11 in order to provide an electrical bridge between the energized area 17 and area 15 through the louver springs bands 35 and the conductive pin 31 . In use, the thrust spring 25 forces the conductive pin 31 away from the energized area 17 . With the spring 25 fully extended, the conductive pin 31 remains fully in the unenergized area 15, and is unenergized. Insertion of the male plug 1 so as to force the conductive pin 31 into the bore 11 produces an electrical bridge across the insulator 19 and creates an electrical circuit between the male plug 1 and the female socket 9. The electrical path goes from the energized area 17 to area 15 via the louver spring bands 35 and the conductive pin 31 , and then from the previously unenergized area 15 to the contact mating area 3 of the male plug 1 . Neither of the two embodiments discussed above should be connected or disconnected under load. Figure 6 shows an alternate male plug 1 which has a contact mating area 3 , a mating pin 5 and an insulated male contact tip 7 . It will be appreciated that, although two particular embodiments of the invention have been described and illustrated in detail, various changes and modifications may be made. One such modification is that the dog leg lock 29 may be omitted if the male plug 1 is not of a specific single-pole connector family produced by Litton.

Claims: A female contact (9) for receiving and electrically connecting a male plug (1), comprising: an outer sleeve (13) having a large diameter entry bore (11) for receiving and contacting said male plug (1), an inner portion (17) of said entry bore (11) being electrically energized, an outer portion (15) of said entry bore (11) being electrically unenergized, a biased plunger (20) within the sleeve (13), adapted to move in response to an inwardly directed force by said male plug (1) from a first position, for preventing unauthorized access from said outer portion (15) to said inner portion (17), to a second position, for electrically connecting said male plug (1) to said energized inner portion (17), and a spring (25) which, when uncompressed, biases said biased plunger (20) to said first position, characterized by conductive means (35) to connect said inner portion (17) and said outer portion (15) when said spring (25) is compressed. The female contact of claim 1, wherein said conductive means further includes: a pair of louver springs (35) surrounding a conductive pin (31) such that an outermost one of said louver springs (35) contacts said outer portion (15) and an innermost one of said louver springs (35) contacts said inner portion (17) when said biased plunger (20) is in said second position, thereby providing electrical contact between said inner portion (17) and said outer portion (15) for energizing said male plug (1). The female contact of claim 1, wherein said biased plunger (20) is recessed within the bore (11). The female contact of claim 1, wherein said biased plunger (20) contains sharp points at its outer edge to further prevent unauthorized access to the inner portion. The female contact of claim 1, wherein said inner portion is terminated by cable termination means (27). The female contact of claim 5, wherein said cable termination means comprises one of either a threaded bolt (27), a crimp, a solder barrel or a flat blade.

Inventors: BERNARDINI ALLEN J, BERNARDINI, ALLEN J.
Applicants: LITTON SYSTEMS INC, LITTON SYSTEMS, INC.
Application year: 1998
Main classification: H01R13
IPC codes: H01R13