Abstract:
An improved surge suppressor which combines a ground fault circuit interrupter with overvoltage protection for AC power lines. The surge suppressor includes a switchable device for disconnecting power from the ground fault circuit interrupter in the event the AC neutral is lost.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an improved surge suppressor which combines a ground fault circuit interrupter with overvoltage protection for AC power lines. The surge suppressor includes a switchable device for disconnecting power from the ground fault circuit interrupter in the event the AC neutral is lost. 
     2. Discussion Of The Related Art 
     Apparatus which combine a ground fault circuit interrupter (“GFCI”) with AC overvoltage protection are known. One such apparatus is shown in U.S. Pat. No. 5,654,857 and U.S. Pat. No. 5,841,615, both issued to Bernard Gershen. These patents disclose a GFCI in combination with MOVs connected between the AC line and the AC neutral, between the AC line and ground and between the AC neutral and ground. Another such apparatus is shown in U.S. Pat. No. 6,212,048 B1 issued to Nisar A. Chaudhry, which discloses a GFCI in combination with overvoltage protection between the AC line and the AC neutral and which provides overvoltage protection for electrical equipment without using a separate ground conductor. Instead, a “virtual ground” circuit is employed which simulates the ground conductor. None of the apparatus disclosed in these patents deals with the loss of the AC neutral, which can occur if the neutral bar at the service entrance corrodes, something which occurs not infrequently in salt air environments. 
     SUMMARY OF THE INVENTION 
     The present invention combines a GFCI with AC overvoltage protection and also uses a switchable device to disconnect the power from the GFCI in the event the AC neutral is lost. The preferred embodiments employ a relay with the coil connected between the AC line and the AC neutral. The AC line and the AC neutral are connected to a set of input relay contacts. The GFCI is connected to the AC line and the AC neutral through a set of output relay contacts. Under normal operating conditions the relay is energized and power flows through the relay to the GFCI via the relay contacts. If the AC neutral is lost, the relay is deenergized and the contacts open, thereby disconnecting power from the GFCI. The GFCI preferably has one or more AC outlets for receiving three-prong AC plugs. 
     The subject matter which I regard as my invention is more particularly pointed out in the claims at the end of the specification. The invention, including its method of operation and its numerous advantages, may best be understood by reference to the following description taken in conjunction with the accompanying drawings wherein like numerals refer to like components. 
    
    
     DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic diagram of a first embodiment of the invention; 
     FIG. 2 is a schematic diagram of a second embodiment of the invention; 
     FIG. 3 is a schematic diagram of a third embodiment of the invention; 
     FIG. 4 is a schematic diagram of a fourth embodiment of the invention; and 
     FIG. 5 is a schematic diagram of a fifth embodiment of the invention. 
    
    
     DETAILED DESCRIPTION 
     FIG. 1 is a schematic diagram of a first embodiment of the invention. The surge suppressor  10  has conductors  12 ,  14  and  16  adapted to be connected, respectively, to the AC line, the AC neutral and ground. The surge suppressor preferably has overvoltage protection connected between the AC line and the AC neutral, between the AC line and ground and between the AC neutral and ground. The overvoltage protection between the AC line and the AC neutral comprises thermal sensing fuse  18  and MOV  20 . The overvoltage protection between the AC line and ground comprises thermal sensing fuse  22  and MOV  24 . The overvoltage protection between the AC neutral and ground comprises thermal sensing fuse  26  and MOV  28 . Thermal sensing fuses  18 ,  22  and  26  may all be G4A01084C made by Thermodisc Incorporated, 1320 South Main Street, Mansfield, Ohio. MOVs  20 ,  24  and  28  may all have a breakdown voltage of 130 volts. 
     Connected to the AC line and the AC neutral is a switchable device in the form of a single pole, double throw relay  30 . The coil of relay  30  is connected between the AC line and the AC neutral so that, when the surge suppressor is connected to a source of AC power, the relay is energized. Contacts  32  and  34  of relay  30  are also connected to the AC line and the AC neutral, respectively. Connected to contacts  36  and  38  of relay  30  is a GFCI device  40  which has two receptacles  42 ,  44  for receiving three-prong AC plugs. GFCI  40  is also connected to ground. Under normal operating conditions, AC power is provided to GFCI  40  through contacts  32 ,  36  and  34 ,  38  of relay  30 . If the AC neutral is lost, however, relay  30  becomes deenergized and contacts  32 ,  36  and  34 ,  38  open, thereby removing power from GFCI  40 . Relay  30  may be K10P-11A15-120 made by Tyco Electronics, Menlo Park, Calif. GFCI  40  may be a GF15B-K made by Eagle Electric Manufacturing Co., Long Island City, N.Y. While surge suppressor  10  in FIG. 1 uses a switchable device in the form of an electromechanical relay to sense the loss of the AC neutral and disconnect power from the GFCI, other equivalent apparatus may also be employed. For example, a solid state switchable device may be used and would be equally effective. 
     FIG. 2 is a schematic diagram of a second embodiment of the invention. Surge suppressor  50  comprises resistor  52 , diode  54  and light emitting diode (LED)  56  which provides a visual indication of normal operation. When the surge suppressor  50  is connected to a source of AC power LED  56  will be lighted if both the AC line and the AC neutral are present. 
     FIG. 3 is a schematic diagram of a third embodiment of the invention. The embodiment of FIG. 3 differs from the embodiments of FIGS. 1 and 2 in the nature of the AC overvoltage protection and in that some filtering is provided. In surge suppressor  60  the overvoltage protection between the AC line and the AC neutral, between the AC line and ground and between the AC neutral and ground comprises, in each instance, the series combination of a thermal sensing fuse, an MOV and a gas discharge tube (GDT). MOVs  62 ,  66  and  70  may have a breakdown voltage of 95 volts. GDTs  64 ,  68  and  72  may have a breakdown voltage of 425 volts. Filtering is provided by inductor  74  and capacitor  76 . Inductor  74  may be 3.4 microhenries and capacitor  76  may be 0.22 microfarads. The series connection of the MOV and GDT eliminates leakage current through the MOV and prolongs the life of the MOV. 
     FIG. 4 is a schematic diagram of a fourth embodiment of the invention. The embodiment of FIG. 4 is similar to the embodiment of FIG. 3 except that the embodiment of FIG. 4 has additional overvoltage protection between the AC line and the AC neutral comprising thermal sensing fuse  82 , MOV  84  and GDT  86 . In the embodiment of FIG. 4, MOV  84  may have a breakdown voltage of 95 volts while MOV  62  may have a breakdown voltage of 120 volts. 
     FIG. 5 is a schematic diagram of a fifth embodiment of the present invention. Relay  30  and GFCI  40  are the same as in the other embodiments. The AC overvoltage protection is different in that it employs MOVs  92 ,  94  and  96  with integral fusing elements. MOVs  92 ,  94  and  96  may be obtained from Maida Development Company, 20 Libby Street, Hampton, Va. as part number D6521ZOV131 RA20. MOVs  92 ,  94  and  96  may have a breakdown voltage of 130 volts. 
     While the present invention has been described by reference to various preferred embodiments, it will be understood by persons skilled in the art that many modifications and variations may be made in those preferred embodiments without departing from the spirit and scope of the present invention.