Abstract:
A power transfer device plugs into a standard power meter box and a power meter plugs into the transfer device. Power transfer is accomplished by a lever operated plate which operates two circuit breakers in unison. The conductors in the transfer device are primarily bus bars. The circuit breakers may be replaced by switches and overload protection devices and a power meter may be built into the power transfer device.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the benefit of U.S. Provisional Patent Application No. 60/156,623, filed Sep. 27, 1999. 
    
    
     FIELD OF THE INVENTION 
     The subject invention is in the field of electrical switches, switching systems and overload protection devices. In particular, it is in the field of apparatus for disconnecting an electrical system from one source of power and connecting it to another and vice versa, a primary example being disconnecting the electrical system of a building from the electrical utility power supply and connecting to an auxiliary generator power supply. 
     BACKGROUND OF THE INVENTION 
     Apparatus for disconnecting an electrical system from one source of power and connecting it to another, and vice versa, is widely used in boats, home, factories, hospitals and the like. In the majority of installations of such switching, the switching is implemented by adding wiring and switches to the electrical power system. However, installations which incorporate an electrical utility meter which is plugged into a receptacle offer the possibility of implementing the power supply switching with a minimum of wiring. The control apparatus disclosed in U.S. Pat. No. 3,654,484, issued Apr. 4, 1972 to Jorgensen et al., is an example of power supply switching which takes advantage of the possibility. The Jorgensen et al. apparatus plugs into the utility meter plug and the utility meter is plugged into the apparatus. The apparatus comprises a receptacle for plugging in a connector from an auxiliary power supply and a switch which connects the electrical system to either the utility power supply or the auxiliary power supply. The Jorgensen et al. apparatus was marketed by the Onan Corporation under size and costs constraints which rendered the apparatus economically and practically feasible. However, because of these restraints, the switching in the Onan product did not meet utility standards in terms of safety, reliability, longevity and overload protection. 
     The present invention is directed to an apparatus that meets these needs and other shortcomings in the prior art. 
     SUMMARY OF THE INVENTION 
     The subject invention is a power transfer device that plugs into a power meter receptacle. The device may further comprise a power meter or a receptacle for a power meter. Utility system power flows into the device from the power meter receptacle (box). It also comprises a receptacle for plugging in an alternate or auxiliary power supply. Electrical conductors, preferably bus bars, conduct power from the utility systems through the meter and into the served system or from the auxiliary power socket into the served system. The device also comprises switches for connecting one or the other power supply to the served electrical system. In a preferred embodiment, the switches are commercially available circuit breakers. The invention can also be implemented using switches and overload protection devices, such as fuses. 
     A mechanism is provided for operating both switches in unison and may allow an off position in which neither switch is on. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The foregoing aspects and many of the attendant advantages of this invention will become more readily appreciated as the same become better understood by reference to the following detailed description, when taken in conjunction with the accompanying drawings, wherein: 
     FIG. 1 is a general view of one embodiment of the subject invention installed on a standard power meter box; 
     FIG. 2 is an exploded view of the components of the FIG. 1 embodiment with the housing of the standard power meter box transparent to show details; 
     FIG. 3 is an exploded view of a preferred embodiment of the subject transfer switch; and 
     FIG. 3A is an enlarged view showing installation of circuit breaker stabs in detail. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The subject invention is a power transfer device that, in one embodiment, plugs into a power meter receptacle. The device may further comprise a receptacle for a power meter. FIG. 1 is a general view of one embodiment  42  of the subject invention installed on a standard power meter box  34 . Socket  34 A in fitting  34 B receives power from a utility system. Socket  28  is an auxiliary power inlet. Lever  24  is used to operate the transfer switch. Power meter  35  is plugged into meter socket  35 A in the transfer device. 
     FIG. 2 is an exploded view of the components of the FIG. 1 embodiment with the housing  34 C of meter box  34  transparent to show details. Conductors L 1  and L 2  feed power to meter jaws  36  and  36 A. Conductor L 3  is the neutral wire and is connected to neutral/ground bus  5 . Conductor L 3 A is connected to the ground bus and extends into the served electrical system. 
     Set screw  44  serves to retain conductor L 3 A in the neutral bus and has a threaded hole in the bottom of its hex socket to enable use of screw  45  to connect ground wire  41  of the transfer switch to the neutral/ground system of the served system. Conductors L 1 A and L 2 A are connected to jaws  37  and  37 A and carry power into the served system. 
     Meter ring  39  is used to retain the power meter on the transfer device and is locked in place by seal  40 . 
     FIG. 3 is an exploded view of a preferred embodiment of the transfer switch with some parts numbered as in FIG.  2 . Blade  6 A on utility input bus bar  6  and blade  7 A on utility input bus bar  7  engage jaws  36 A and  36 , respectively. Blade  8 A on output bus bar  8  and blade  9 A on output bus bar  9  engage jaws  37 A and  37 , respectively. 
     Breaker stabs  11 ,  11 A,  12 , and  12 A are electrical connectors which are provided with circuit breakers. Stabs  11  and  12  connect bus bars  8  and  9 , respectively, to circuit breaker  18  and stabs  11 A and  12 A connect bus bars  8  and  9 , respectively, to circuit breaker  17 . Specifically, stabs  11  and l A are connected to bus bar  8  and stabs  12  and  12 A are connected to bus bar  9 . The installation of these stabs is shown in detail in FIG. 3A with parts numbered as in FIG.  3 . Each circuit breaker has an off state and an on state. 
     Slot  20 A in part  20  engages lever  17 A of circuit breaker  17 . Slot  20 B in part  20  engages lever  18 A of circuit breaker  18 . Part  20  is moved laterally by lever  24  and is connected to the lever by screw  22 . The lever is pivoted on screw  23  which fits through hole  27 A in face plate  27  and is retained by nut  26 . The motion of part  20 , called the interlock plate, is arcuate. Slots  20 A and  20 B are long enough to allow for the radial component and the circumferential motion of the interlock plate provides the lateral motion which actuates the circuit breakers. 
     Conductors  30  and  31  connect power terminals in socket  28  to circuit breaker  18 . Conductors  32  and  33  connect the neutral/ground terminal in socket  28  to neutral/ground bus  5 . 
     In normal (non-emergency) use, circuit breaker  17  is on (conducting), circuit breaker  18  is off (non-conducting) and power from the utility flows via the jaws, blades and bus bars described above through the transfer device, through the meter and back through the transfer device and circuit breakers  17 , through the meter base into the served system. 
     In emergency use, circuit breaker  17  is off and circuit breaker  18  is on. Power flows from socket  28  through conductors  30  and  31  to circuit breaker  18  and then through bus bars, blade and jaws to conductors L 1 A and L 2 A and thereby into the served system. The ground/neutral terminal is connected to conductor L 3 A via conductors  32  and  33  and neutral bus  5 . Auxiliary power is not metered by the meter. 
     In alternate embodiments of the subject invention, a power meter may be incorporated in the device rather than being plugged into it and/or the circuit breakers may be replaced with non circuit breaker switches, in combination with overload protection devices, such as fuses. 
     The present invention provides a power transfer device that accommodates a power meter and meets marketing constraints in terms of size, cost, safety, reliability, and longevity and also provides overload protection. Meeting the constraints is enabled by the use of proven, commercially available circuit breakers as the switching means and the use of bus bars instead of wiring to optimize power carrying capability relative to the space required. 
     It is also considered to be understood that while one embodiment of the invention is disclosed herein, other embodiments and modifications of the one described may fall within the scope of the invention which is limited only by the attached claims.