Test protection circuit with overvoltage protection

Abstract

The present invention provides a test protection circuit with a ground fault circuit interrupter (GFCI) having end-of-life automatic monitoring and overvoltage monitoring. The present invention also provides a relay synchronization switch for isolating the GFCI during automatic monitoring. The test protection circuit also provides an end-of-life circuit that disables the test protection circuit if the automatic monitoring fails, and a cutoff circuit that disables the test protection circuit if an overvoltage condition is detected.

Description

Technical Field

[0001] The present invention relates generally to electrical safety devices and, more particularly, to an automatically resetting ground fault circuit interrupter (GFCI) having an automatically monitored end-of-life circuit and overvoltage monitoring. Background Art

[0002] Conventional electrical equipment generally receives alternating current (AC) from a power source such as an electrical outlet through a pair of conductive lines. This pair of conductive lines, usually called phase and neutral, enables the appliance or load to receive the current required for operation.

[0003] Connecting electrical equipment to the power supply via a pair of conductive lines creates a number of potentially hazardous conditions. In particular, there is the risk of ground faults and grounded neutral conditions in the conductive lines. A ground fault condition occurs when there is an imbalance between the currents flowing in the phase and neutral conductors. A grounded neutral condition occurs when the neutral conductor is grounded at the load. Ground fault conditions are extremely dangerous and can result in serious injury.

[0004] Ground fault interrupters include ground fault circuit interrupters, ground fault receptacles, and even ground fault protection devices for cable installations. Even if ground fault interrupters pass all current industry standards, they can cause trouble due to nuisance tripping. One reason for nuisance tripping is the disconnection of power to inductive equipment, especially by unplugging the equipment.

[0005] Examples of these devices include electric shavers, high intensity lamps, and small cooling fans, such as those used to cool electronic equipment. Unplugging these devices can cause arcing between the plug and the receptacle, resulting in several volts of broadband noise being superimposed on the power line. Due to the broadband nature of the noise, even very small stray coupling capacitances can couple noise from the power line conductors into the ground fault circuit, causing nuisance tripping.

[0006] A typical ground fault interrupter includes an operational amplifier that amplifies the sensed ground fault signal and applies the amplified signal to a window comparator, which compares the signal to positive and negative reference signals. If either reference value is exceeded, a trip signal is generated. A common type of ground fault detection circuit is a dormant oscillator type detector. This detector includes a first sensor coil through which the phase and neutral conductors of the protected circuit pass. The output of the first sensor coil is applied to the above-mentioned operational amplifier via a coupling capacitor, which is followed by a window comparator. A phase-to-ground fault causes the amplified signal to exceed the reference value and generate a trip signal.

[0007] The dormant oscillator type ground fault detector includes a second sensor coil through which only the neutral conductor passes. A neutral-to-ground fault couples the two detector coils together, causing the amplifier to oscillate, which oscillation results in the generation of a trip signal.

[0008] It has been discovered that broadband noise caused by load-related switching events, such as that caused by unplugging an inductive device, can cause nuisance tripping of ground fault interrupters.

[0009] Ground fault circuit interrupters are well known in the art and are commonly used to protect against ground fault and grounded neutral conditions. Generally speaking, a GFCI device senses the presence of a ground fault and grounded neutral condition in a conductive line and, in response, disconnects at least one of the conductive lines between a power source and a load to eliminate the hazardous condition.

[0010] In U.S. Pat. No. 5,177,657, inventors M. Baer et al., a ground fault interrupter circuit is disclosed that interrupts the flow of current to a pair of lines extending between a power source and a load. The ground fault interrupter circuit includes: a circuit breaker including a normally open switch disposed on one or both of the two lines, a relay circuit for selectively closing the normally open switch, an electronic latch circuit capable of operating in a first bistable state and a second bistable state, and a fault sensing circuit for sensing the presence of a fault condition in at least one of the lines. When the electronic latch circuit is in the first bistable state, the electronic latch circuit causes the relay circuit to close the normally open switch and maintain the normally open switch in its closed position. When the latch circuit is in its second bistable state, the electronic latch circuit also causes the relay circuit to allow the normally open switch to return to its normally open state. The fault sensing circuit senses the presence of a fault condition in at least one of the lines and causes the electronic latch circuit to latch in its second state when the fault condition is detected.

[0011] In U.S. Pat. No. 5,418,678, inventor T.M. McDonald, an improved ground fault circuit interrupter (GFCI) device is disclosed that requires manual setup upon initial connection to an AC power source or after a power interruption. The improved GFCI device utilizes a controlled switching device that is responsive to a load power signal to allow the relay contact set of the GFCI device to close only when power is available at the output or load terminals. The controlled switching device preferably includes an optoisolator or other type of switching device that provides isolation between the GFCI input and output terminals when the relay contact set is open. The improved GFCI device can be incorporated into a portable unit, such as a plug-in or line-cable unit, for use with an unprotected AC outlet.

[0012] In U.S. Pat. No. 4,816,957, inventor LFIrwin, an adapter unit is disclosed that includes a moisture-proof housing in which an improved, self-testing ground fault interrupter device is mounted. This improved device is electrically interconnected with a connector mounted on the outside of the adapter housing so that the unit can be directly plugged into a standard duplex outlet of an existing circuit. The device includes circuitry that automatically tests the operability of the device when it is plugged into the duplex outlet without requiring manual operation of a test button or other overt action by the user.

[0013] In U.S. Pat. No. 4,578,732, inventors C. W. Drapper et al., a wall socket type ground fault circuit interrupter is disclosed, which has a pair of sockets accessible from the front of the interrupter, a reset button and a test button. The interrupter has a latched snap-action contact and a novel latching relay structure for holding the snap-action contact in the circuit-on position. The snap-action contact allows all components including the monitoring toroidal coil (sensing transformer) and the power supply to be positioned and connected separately on the load side of the snap-action contact so that when the contact moves quickly to the circuit-off position, all circuits of the interrupter are de-energized. The snap-action contact mechanism and relay are provided with several structures that provide a non-trip mode contact actuation for the interrupter and thus provide a snap-action contact operation that prevents tampering.

[0014] One disadvantage of the above-described type of GFCI device is that the GFCI device typically includes a large solenoid for selectively opening and closing the switching device. Specifically, the solenoid typically requires a constant supply line voltage (approximately 120 volts) in order to switch and maintain the solenoid in its energized state. As a result, the solenoid becomes a significant source of power consumption.

[0015] UL943 now requires panel-mount and receptacle-based GFCIs to indicate "end of life" if the device fails to trip when the test button is manually operated. However, even if the end user tests their devices regularly, a GFCI device that has not been properly tested may reset and continue to provide power but not provide ground fault protection. Without a built-in power rejection feature, consumers may mistakenly and tragically believe that if there is power, there is protection. Despite manufacturers' warnings, many end users were (and continue to be) unaware of the need for regular testing; others are aware of regular testing, but do not always test diligently. UL will also introduce a requirement for automatically monitoring GFCIs, whereby the GFCI will test itself at regular intervals and provide an "end of life" indication to the user.

[0016] Generally speaking, the end-of-life events are an open or shorted ground fault sensing component (toroid and integrated circuit); a fault in the trip solenoid and / or its control circuit, or an open or shorted switching semiconductor (SCR) controlling the trip solenoid control circuit.

[0017] Therefore, there is a need for a sufficiently rated solenoid for a line voltage GFCI device that has a reduced tendency to fail due to the high voltages and currents associated with typical line voltages. There is also a need for a ground fault interrupter that does not nuisance trip in response to broadband noise in the protected circuit. There is also a need for such a ground fault circuit that has improved immunity to broadband noise also generated in response to sputtering arc faults.

[0018] There is also a need for a GFCI that can manually and automatically test commonly failed components in the GFCI and deny power if the test fails. Summary of the invention

[0019] A GFCI constructed according to the present invention is used to interrupt the current flowing through a pair of lines extending between a power source and a load, and the GFCI includes: a circuit breaker having a switch arranged on one of the lines, the switch having a first position and a second position, in which the power source in its associated line is not connected to the load in the first position and the power source in its associated line is connected to the load in the second position; a relay circuit for selectively moving the switch and maintaining the switch in the first position or the second position.

[0020] The GFCI includes a latch circuit capable of operating in a first bistable state and a second bistable state (on / off), the latch circuit allowing the solenoid to switch from its de-energized state to its energized state and remain in its energized state when in the first bistable state, and allowing the solenoid to switch from its energized state to its de-energized state and remain in its de-energized state when in the second bistable state.

[0021] The GFCI includes a fault detection circuit for detecting the presence of a fault condition in at least one of the lines extending between the power source and the load and causing the latch circuit to latch in its second bistable state upon detection of the fault condition. The fault detection circuit includes: a low power ground fault interrupter integrated circuit and an SCR driver; and at least one passive RF noise suppressor for preventing RF noise from being amplified by the integrated circuit and accidentally triggering the SCR driver. The GFCI also includes a light emitting diode circuit for indicating that the GFCI is operating normally.

[0022] Other objects, features and advantages of the present invention will be described in part in the following detailed description, and in part will become clear from the detailed description or may be learned by practicing the present invention. In the detailed description, reference is made to the accompanying drawings, which form a part of the detailed description, and in which specific embodiments for practicing the present invention are illustrated by way of illustration. These embodiments will be described in sufficient detail to enable those skilled in the art to practice the present invention, and it should be understood that other embodiments may be utilized and structural changes may be made without departing from the scope of the present invention. Therefore, the following detailed description should not be interpreted in a limiting manner, and the scope of the present invention is most appropriately defined by the appended claims. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] The accompanying drawings are incorporated herein and constitute a part of this specification, and these drawings illustrate various embodiments of the present invention and are used to explain the principles of the present invention together with the detailed description. In the accompanying drawings, the same reference numerals represent the same parts:

[0024] Figure 1 is a schematic circuit diagram of an automatically resetting ground fault circuit interrupter (GFCI) having the monitoring features and overvoltage features of the present invention; and

[0025] Figure 2 yes Figure 1 Graphical representation of the timing relationships of the monitoring features shown. DETAILED DESCRIPTION

[0026] The following brief definitions of terms should be used throughout this application:

[0027] The term "including" means including but not limited to, and should be interpreted in the same manner as it is generally used in a patent context;

[0028] The phrases "in one embodiment", "according to one embodiment", etc., generally mean that the particular feature, structure, or characteristic following the phrase may be included in at least one embodiment of the present invention, and may be included in more than one embodiment of the present invention (importantly, these phrases are not necessarily referring to the same embodiment);

[0029] If the specification describes something as "exemplary" or an "example," it should be understood to mean a non-exclusive example;

[0030] If the specification states that a component or feature "may", "could", "would", "should", "preferably", "likely", "generally", "optionally", "for example" or "might" (or other such language) be included or have a certain property, that particular component or feature is not necessarily included or has that property.

[0031] Referring now to the drawings, in particular Figure 1 , there is shown a ground fault circuit interrupter (hereinafter referred to as "GFCI") circuit constructed in accordance with the teachings of the present invention, the GFCI being generally indicated by the reference numeral 11.

[0032] As will be discussed in detail below, the GFCI 11 protects the load from a ground fault condition after initially connecting the input terminal L to the load terminal L and connecting the input terminal N to the load terminal N. Furthermore, once the GFCI 11 has protected the load from a ground fault condition, the GFCI 11 can be reset to protect against additional ground fault conditions.

[0033] GFCI 11 includes circuit breaker 13, relay circuit 15, power circuit 17, fault detection circuit 21, bistable electronic latch circuit 23, and test circuit 27. GFCI 11 also includes an automatic monitoring end-of-life module, which includes a relay synchronization switch 31, a simulated ground fault generator 33, automatic monitoring and end-of-life logic circuit, and an end-of-life switch 35A.

[0034] The circuit breaker 13 includes a pair of single-pole double-throw switches SW1 and SW2, which are respectively arranged in the phase line and the neutral line between the power supply and the load. The function of the circuit breaker 13 is to selectively open and close the pair of conductive lines. The switches SW1 and SW2 can be placed in either of two connection positions. In the first connection position or the disconnection position, i.e. Figure 1 In the position shown, switches SW1 and SW2 are positioned so that the input power is not connected to the load. Figure 1 In the relative positions shown, switches SW1 and SW2 are positioned so that the input power is connected to the load. In both positions, the input power is connected to the power circuit 17.

[0035] The relay circuit 15 is used to selectively place the circuit breaker 13 in its first connection position or the second connection position. The relay circuit 15 includes a solenoid RL1a, a transistor Q2 15A, and a bias circuit including a resistor R21 and a Zener diode ZD2.

[0036] Solenoid RL1a is linked with the circuit breaker 13 contacts of switches SW1 and SW2 and is responsible for selectively controlling the connection position of switches SW1 and SW2. Before power is supplied to GFCI 11, solenoid RL1a places switches SW1 and SW2 in the first connection position as shown. When switches SW1 and SW2 are engaged and solenoid RL1a is energized, solenoid RL1a maintains switches SW1 and SW2 in the second connection position.

[0037] Transistor Q2 is a high voltage transistor that controls the flow of current through the energized solenoid RL1a. When transistor Q2 is "off", the flow of current through the solenoid RL1a is disabled and RL1a is de-energized. When transistor Q2 is "on", current flows through the solenoid RL1a, energizing RL1a.

[0038] The power circuit 17 provides power to the GFCI circuit 11. The power circuit 17 includes a rectifier diode D17 and a capacitor C12. Figure 1 Also shown is a varistor MOV1 with a value of 150 volts for protection against surges from the AC power supply. Silicon rectifier D17 and capacitor C12 convert the line AC current from the power supply to DC current.

[0039] When switches SW1 and SW2 are in their second connection positions, the fault detection circuit 21 detects both ground faults in the conductive line and neutral ground conditions. The fault detection circuit 21 includes a sensing transformer T1, a grounded neutral transformer T2, a coupling capacitor C7, a feedback resistor R3, and a ground fault interrupter integrated circuit (IC) (GFCIIC).

[0040] Sense transformer T1 senses the current difference between the phase and neutral conductors and, in the event of a ground fault condition, transformer T1 induces an associated output from its secondary winding. Grounded neutral transformer T2 works in conjunction with transformer T1 to sense the presence of a grounded neutral condition and, in turn, induces an associated output. Coupling capacitor C7 couples the AC signal from the secondary winding of transformer T1 to the GFCIIC.

[0041] After detecting a ground fault or grounded neutral condition, the GFCIIC generates an output pulse on pin 5 to activate latch circuit 23. The activated latch circuit 23 deactivates or de-energizes solenoid RL1a via relay sync switch 31. Latch circuit 23 includes a silicon controlled rectifier SCR1 that can operate in a conducting or non-conducting state.

[0042] Rectifier SCR1 selectively turns transistor Q2 on and off in relay circuit 15 via relay synchronizing switch 31, as will be discussed in greater detail herein. Reset switch SW4 is a conventional push-in switch that, when depressed, removes the holding current from the anode of rectifier SCR1, thereby turning rectifier SCR1 off if rectifier SCR1 is in its conducting state.

[0043] Resistor R2 and capacitor C4 act as a filtering circuit to smooth the varying DC voltage provided by the power supply and provide the filtered DC voltage to the power input of IC U1. As discussed in more detail herein, C4 also provides a temporary GFCIIC VCC when GFCI 11 is in the automatic, auto-monitoring mode.

[0044] The test circuit 27 provides a means of testing whether the circuit 11 is functioning properly. The test circuit 27 includes a current limiting resistor R12 and a test switch SW3 having a conventional push-in design. When the test switch SW3 is pressed to energize the test circuit 27, the resistor R12 provides a simulated fault current similar to a ground fault condition to the transformer T1.

[0045] In use, the GFCI 11 functions in the following manner. Prior to initial connection, switches SW1 and SW2 are normally in Figure 1 The first connection position is shown.

[0046] After one end of the GFCI 11 is initially connected to the power source, a line voltage of approximately 120 volts RMS is applied to the solenoid RL1a through the power circuit 17. The switches SW1 and SW2 are engaged (with Figure 1 The power from the power supply circuit 17 maintains the switches SW1 and SW2 in their connected positions via the solenoid RL1a.

[0047] While the solenoid RL1a is maintained in its energized state, the rectifier SCR1 is in a non-conductive state and the transistor Q2 is turned on, which allows current to flow through the solenoid RL1a through Q2 to the neutral line. Once a ground fault or a grounded neutral condition is detected, the fault detection circuit 21 sends a gate signal to the rectifier SCR1, causing the rectifier SCR1 to be in a conductive state, which in turn turns off the transistor Q2 via the relay synchronous switch. With the transistor Q2 turned off, current does not flow through the solenoid RL1a, and therefore, the solenoid RL1a becomes de-energized. Once de-energized, the solenoid RL1a returns the switches SW1 and SW2 to their first non-connected position, thereby interrupting power from the power source to the load.

[0048] Once the fault condition is removed, the circuit 11 can be reset by pressing switch SW4. Pressing switch SW4 causes the SCR1 holding current to be removed, which causes rectifier SCR1 to turn off. This in turn causes transistor Q2 to turn back on when switch SW4 is released, causing solenoid RL1a to be re-energized. It should be understood that the power supply to the load requires the engagement of switches SW1 and SW2.

[0049] 120 / 240 switch

[0050] The 120 / 240 switch 201 monitors power from the power circuit 17. During normal operation, i.e., when the input power is 120V AC, the 120 / 240 switch 201 provides a ground or neutral path for the solenoid current to flow through solenoid RL1a through Q2 to neutral. If the 120 / 240 switch 201 senses an overvoltage condition, such as 240V AC, the 120 / 240 switch 201 removes the neutral path provided for the solenoid current to flow through solenoid RL1a, thereby de-energizing RL1a and opening switches SW1 and SW2.

[0051] Automatic monitoring and end of life

[0052] The monitoring module 101 includes a relay synchronization switch 31, a simulated ground fault generator 33, an automatic monitoring and end-of-life circuit 35, and an end-of-life switch 35A.

[0053] The simulated ground fault generator (SGFG) 33 contains the logic and devices required to simulate a periodic ground fault. Figure 2 During normal GFCI operation, the SGFG 33 is off. During the automatic monitoring window, the SGFG generates a short circuit on pulse, setting the basic timing of the automatic monitoring end of life (EOL) window. The SGFG pulse is sensed as a ground fault by the GFCI circuit 21. Upon detecting this simulated ground fault, the GFCI IC generates an output pulse at pin 5 to activate the latch circuit 23 (SCR1).

[0054] When the SGFG 33 generates a short circuit open pulse for the purpose of automatically monitoring the ground fault detection circuit 21, the SGFG pulse is also sensed by the GFCI relay sync switch 31, which includes the logic and devices required to temporarily isolate the normal GFCI fault detection described above. The GFCI components under test include the sensing transformer T1, the grounding transformer T2, the GFCI IC, and the bistable electronic latch circuit 23.

[0055] It will be appreciated that the timing window or pulse period set by the SGFG is of sufficiently short duration that when K1 15 is temporarily isolated by the relay sync switch 31 during the automatic monitoring EOL window, the charge on capacitor C4 is sufficient to maintain power to the GFCI IC for the duration of the automatic monitoring EOL window.

[0056] The auto-monitor and EOL logic (monitoring) circuit 35 determines the number of times SCR1 does not turn on during consecutive auto-monitor EOL windows. Figure 2As shown, if the test question "SCR1 is on?" is "off", then SCR1 is not turned on. If SCR1 is not turned on for a predetermined number of times, the GFCI fault detection circuit is faulty and the EOL switch 35A is activated, thereby de-energizing the solenoid K1.

[0057] The invention described above is intended to be exemplary only, and those skilled in the art should be able to make various modifications and variations without departing from the spirit of the invention. All these modifications and variations are intended to fall within the scope of the invention defined by the appended claims.

Claims

1. A test protection circuit for interrupting a current flowing through a pair of lines, wherein: One of the pair of lines extends between a phase line input terminal and a phase line output terminal, and the other line extends between a neutral line input terminal and a neutral line output terminal. The test protection circuit comprises a GFCI (11), a monitoring module (101) integrated with the GFCI (11), and a 120 / 240 overvoltage monitoring circuit (201), wherein the GFCI (11) comprises: A power circuit (17) for providing current to the GFCI (11); A first switch (SW1), connected between the phase line input terminal and the phase line output terminal, having a first input terminal and a first contact terminal, and including a first position in which power is not supplied and a second position in which power is supplied; a second switch (SW2), connected between the neutral line input terminal and the neutral line output terminal, having a second input terminal and a second contact terminal, including a first position where power is not supplied and a second position where power is supplied, wherein the first switch (SW1) is linked to the second switch (SW2); a relay circuit (15) for controlling the first switch (SW1) and the second switch (SW2), the relay circuit (15) comprising a solenoid (RL1a), a transistor (Q2) and a bias circuit comprising a resistor (R21) and a Zener diode (ZD2), and after one end of the GFCI (11) is initially connected to an electric power source, a line voltage is applied to the solenoid (RL1a) through the power circuit (17), so that the solenoid (RL1a) is energized, thereby maintaining the first switch (SW1) and the second switch (SW2) in a second energized position; a fault detection circuit (21) for detecting a ground fault in the pair of lines, comprising a sensing transformer (T1), a grounded neutral transformer (T2), a coupling capacitor (C7) and a GFCI integrated circuit, wherein the sensing transformer (T1) is used to sense the current difference between the phase line and the neutral line and induce an associated output from its secondary winding when a ground fault condition occurs, the grounded neutral transformer (T2) works together with the sensing transformer (T1) to sense the presence of a neutral ground condition and thereby induce an associated output, and the coupling capacitor (C7) couples an AC signal from the secondary winding of the sensing transformer (T1) to the GFCI integrated circuit; and a first bistable electronic latch circuit (23) for de-energizing the relay circuit (15) when a fault is detected, comprising a rectifier (SCR1) operable in a conductive or non-conductive state; and the monitoring module (101) comprising: a simulated ground fault generator (33) which is turned off during normal GFCI (11) operation and generates a ground fault start pulse during an automatic monitoring window that can be sensed by the fault detection circuit (21) as a simulated ground fault, testing the fault detection circuit (21) and a first bistable electronic latch circuit (23), the first bistable electronic latch circuit (23) being turned on during the ground fault start pulse; a relay synchronous switch (31) which can sense the ground fault start pulse generated by the simulated ground fault generator (33) and isolate the GFCI (11) and the relay circuit (15) for the duration of the ground fault start pulse during the ground fault start pulse, and once a ground fault or neutral grounding condition is detected, the fault detection circuit (21) sends a gate signal to the rectifier (SCR1) to put the rectifier (SCR1) in a conductive state, and then turns off the transistor (Q2) in the relay circuit (15) via the relay synchronous switch (31), thereby de-energizing the solenoid (RL1a); an auto-monitoring logic module (35) for monitoring the first bistable electronic latch circuit (23) during a ground fault turn-on pulse and determining a number of times the rectifier (SCR1) of the first bistable electronic latch circuit (23) does not turn on during a continuous auto-monitoring end-of-life window; and an end-of-life switch (35A) which is activated if the automatic monitoring logic module (35) determines that the rectifier (SCR1) of the first bistable electronic latch circuit (23) has not been turned on for a predetermined number of times, thereby de-energizing the solenoid (RL1a) in the relay circuit (15); The 120 / 240 overvoltage monitoring circuit (201) is used to monitor the power from the power supply circuit (17). It has the function of an on-off switch. During normal operation, the 120 / 240 overvoltage monitoring circuit (201) provides a path for the solenoid current to reach the neutral line through the solenoid (RL1a) via the transistor (Q2). If an overvoltage condition is detected, the 120 / 240 overvoltage monitoring circuit (201) disconnects the solenoid (RL1a) from the neutral line path via the transistor (Q2), thereby de-energizing the solenoid (RL1a) and disconnecting the first switch (SW1) and the second switch (SW2).

2. The test protection circuit according to claim 1, wherein: The fault detection circuit (21) includes a power capacitor (C4) for providing power to the GFCI integrated circuit when the GFCI (11) is isolated by the relay sync switch (31) during a ground fault opening pulse.

3. The test protection circuit as claimed in claim 2, wherein: The ground fault opening pulse period has a sufficiently short duration so that when the relay circuit (15) is isolated by the relay synchronization switch (31), the charge on the power capacitor (C4) is sufficient to maintain the power supplied to the GFCI integrated circuit for the duration of the ground fault opening pulse period.

4. The test protection circuit according to claim 1, wherein: The automatic monitoring logic module (35) includes a predetermined number of failures of the GFCI circuit in response to a simulated ground fault opening pulse to test the GFCI circuit, wherein the GFCI circuit under test includes: Sensing transformer (T1); Grounded neutral transformer (T2); GFCI integrated circuits; and A first bistable electronic latch circuit (23).

5. The test protection circuit according to claim 1, wherein: One end of the 120 / 240 overvoltage monitoring circuit (201) is connected to the power neutral line of the power supply circuit (17), and the other end is connected to the solenoid (RL1a) through the transistor (Q2) to reach the neutral line path. During normal operation, the 120 / 240 overvoltage monitoring circuit (201) connects the power neutral line of the power supply circuit (17) and the path provided by the solenoid (RL1a) through the transistor (Q2) to reach the neutral line to form a loop. If an overvoltage condition is detected, the 120 / 240 overvoltage monitoring circuit (201) will disconnect the solenoid (RL1a) from the neutral line path through the transistor (Q2), thereby releasing the neutral line path provided for the solenoid current to flow through the solenoid (RL1a), de-energizing the solenoid (RL1a) and disconnecting the first switch (SW1) and the second switch (SW2).

6. A method for intermittently testing a component of a GFCI (11) for interrupting power between a phase input terminal and a phase output terminal, the method comprising: Providing a power circuit (17) for providing current to the GFCI (11); A relay circuit (15) is provided for controlling the switch, the relay circuit (15) comprising a solenoid (RL1a), a transistor (Q2) and a bias circuit comprising a resistor (R21) and a Zener diode (ZD2), and after one end of the GFCI (11) is initially connected to an electric power source, a line voltage is applied to the solenoid (RL1a) through the power circuit (17), so that the solenoid (RL1a) is energized, thereby maintaining the first switch (SW1) and the second switch (SW2) in a second energized position; A fault detection circuit (21) is provided for detecting a ground fault in a line, the fault detection circuit (21) comprising a sensing transformer (T1), a grounded neutral transformer (T2), a coupling capacitor (C7) and a GFCI integrated circuit, wherein the sensing transformer (T1) is used to sense the current difference between the phase line and the neutral line and induce an associated output from its secondary winding when a ground fault condition occurs, the grounded neutral transformer (T2) works together with the sensing transformer (T1) to sense the presence of a neutral ground condition and thereby induce an associated output, and the coupling capacitor (C7) couples an AC signal from the secondary winding of the sensing transformer (T1) to the GFCI integrated circuit; providing a first bistable electronic latch circuit (23) for de-energizing the relay circuit (15) upon detection of a fault, comprising a rectifier (SCR1) operable in a conducting or non-conducting state; providing a simulated ground fault generator (33) which is off during normal GFCI (11) operation and used to generate a ground fault test start pulse which can be sensed as a simulated ground fault by the fault detection circuit (21) during the automatic monitoring window to test the fault detection circuit (21) and the first bistable electronic latch circuit (23); A relay synchronization switch (31) is provided, which is capable of sensing the ground fault start pulse generated by the simulated ground fault generator (33), and isolating the GFCI (11) and isolating the relay circuit (15) for the duration of the ground fault test start pulse during the ground fault start pulse, and once a ground fault or neutral grounding condition is detected, the fault detection circuit (21) sends a gate signal to the rectifier (SCR1), so that the rectifier (SCR1) is in a conductive state, and then the transistor (Q2) in the relay circuit (15) is turned off via the relay synchronization switch (31), thereby de-energizing the solenoid (RL1a); turning on a first bistable electronic latch circuit (23) during a ground fault test enable pulse; and providing an automatic monitoring logic module (35) for monitoring the number of times the rectifier (SCR1) of the first bistable electronic latch circuit does not turn on during a ground fault start pulse; providing an end-of-life switch (35A) for de-energizing the relay circuit (15) if the automatic monitoring logic module (35) determines that the rectifier (SCR1) of the first bistable electronic latch circuit (23) has not been turned on for a predetermined number of times; A 120 / 240 overvoltage monitoring circuit (201) is provided for monitoring the power from the power supply circuit (17), and it has the function of an on-off switch. During normal operation, the 120 / 240 overvoltage monitoring circuit (201) provides a path for the solenoid current to reach the neutral line through the solenoid (RL1a) through the transistor (Q2), and if an overvoltage condition is detected, the 120 / 240 overvoltage monitoring circuit (201) disconnects the connection between the solenoid (RL1a) and the neutral line path through the transistor (Q2), thereby de-energizing the solenoid (RL1a) and disconnecting the first switch (SW1) and the second switch (SW2).

7. The method of claim 6, wherein: The fault detection circuit (21) includes a power capacitor (C4) for providing power to the GFCI integrated circuit when the GFCI (11) is isolated by the relay sync switch (31) during a ground fault opening pulse.

8. The method of claim 7, wherein: The ground fault opening pulse period has a sufficiently short duration so that when the relay circuit (15) is isolated by the relay synchronization switch (31), the charge on the power capacitor (C4) is sufficient to maintain the power supplied to the GFCI integrated circuit for the duration of the ground fault opening pulse period.

9. The method of claim 6, wherein: The automatic monitoring logic module (35) includes a predetermined number of failures of the GFCI circuit in response to a simulated ground fault opening pulse to test the GFCI circuit, wherein the GFCI circuit under test includes: Sensing transformer (T1); Grounded neutral transformer (T2); GFCI integrated circuits; and A first bistable electronic latch circuit (23).

10. The method of claim 6, wherein: One end of the 120 / 240 overvoltage monitoring circuit (201) is connected to the power neutral line of the power supply circuit (17), and the other end is connected to the solenoid (RL1a) through the transistor (Q2) to reach the neutral line path. During normal operation, the 120 / 240 overvoltage monitoring circuit (201) connects the power neutral line of the power supply circuit (17) and the path provided by the solenoid (RL1a) through the transistor (Q2) to reach the neutral line to form a loop. If an overvoltage condition is detected, the 120 / 240 overvoltage monitoring circuit (201) will disconnect the solenoid (RL1a) from the neutral line path through the transistor (Q2), thereby releasing the neutral line path provided for the solenoid current to flow through the solenoid (RL1a), de-energizing the solenoid (RL1a) and disconnecting the first switch (SW1) and the second switch (SW2).

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