Abstract:
A new type of ground fault circuit interrupter (GFCI) with reverse wiring protection preferably includes a pair of fixed contact holders, each having a contact at one end; a pair of movable contact holders, each having a fixed end and a movable end, each of the movable ends having a contact; a movable assembly that moves between first and second positions, wherein the first position is a position in which each of the contacts of the fixed contact holders makes contact with one of the contacts of the movable end of one of the movable contact holders, and wherein the second position is a position in which the contacts of the fixed contact holders are separated from the contacts of the movable contact holders; an electromagnetic resetting component, which, when energized, causes the movable assembly to be in the first position; an electromagnetic tripping component, different from the electromagnetic resetting component, which, when energized, causes the movable assembly to be in the second position; and a control circuit, which, upon detection of a fault condition, energizes the electromagnetic tripping component, and which, upon detection of a reset condition, energizes the electromagnetic resetting component.

Description:
CROSS-REFERENCE TO RELATED APPLICATION  
         [0001]    This application claims priority of Chinese Patent Application No. 02131108.0, filed on Oct. 9, 2002, and incorporated herein by reference in its entirety.  
         BACKGROUND OF THE INVENTION  
         [0002]    1. Field of the Invention  
           [0003]    The present invention relates to a ground fault circuit interrupter (GFCI) for load ground-fault protection. More specifically, the invention relates to a GFCI receptacle adopting an electromagnetic tripper and providing reverse wiring protection.  
           [0004]    2. Discussion of Related Art  
           [0005]    Ground fault circuit interrupter (GFCI) devices are designed to trip in response to the detection of a ground fault condition at an AC load. For example, the ground fault condition may result when a person comes into contact with the line side of the AC load and an earth ground at the same time, a situation that can result in serious injury. The GFCI device detects this condition by using a sensing transformer to detect an imbalance between the currents flowing in the line and neutral conductors of the AC supply, as will occur when some of the current on the line side is being diverted to ground. When such an imbalance is detected, a circuit breaker within the GFCI device is immediately tripped to an open condition, thereby opening both sides of the AC line and removing all power from the load.  
           [0006]    A GFCI generally includes a housing, a tripper, a reset button, a test button, a mounting strap with grounding strap and banding screw, a pair of movable contact holders with contacts, a pair of fixed contact holders with contacts, and control circuit. Currently, GFCI is widely used to prevent electric shock and fire caused by ground fault.  
           [0007]    In the past, a GFCI receptacle generally adopted a mechanical actuator. It limited the performance of such products, especially in that these GFCIs did not provide reverse wiring protection. In addition, these mechanical GFCIs required high standards in the quality of the parts and assembling work. Examples of mechanical GFCIs include those disclosed in U.S. Pat. No. 5,933,063 and U.S. Pat. No. 4,802,052.  
           [0008]    The GFCI shown in U.S. Pat. No. 6,252,407 B1 has reverse wiring protection, but it is a visual alarm indicator signaling a miswiring condition to the installer, and if miswired (despite the visual alarm indicator) by connecting the line to the load, the GFCI can still be reset. Under such circumstances, an unknowing user, faced with a GFCI that has been miswired, may press the reset button, which, in turn, will cause the GFCI to be reset without reverse wiring protection available. And, such a GFCI that has been reset is very easy to trip again in events like lightning strikes.  
           [0009]    The design of these GFCIs allows two ways of connection: the load can pass through the entry ports of the face portion or can alternatively connect through the load binding screws. Consequently, an installer or user can still mistakenly connect the line and the load in a reverse direction. When this occurs, without reverse wiring protection, the GFCI will function just as a common receptacle.  
           [0010]    There is still a need for a GFCI that has the following characteristics to improve the safety features of the receptacles: capability of providing reserve wiring protection; highly responsive; convenient to assemble; and having better functionality.  
         SUMMARY OF THE INVENTION  
         [0011]    It is an object of the invention to provide a GFCI circuit that has the above characteristics.  
           [0012]    In general, a preferred embodiment of a ground fault circuit interrupter (GFCI) according to the invention will comprise a pair of first contact holders, each having a contact at one end; a pair of movable contact holders, each having a fixed end and a movable end, each of the movable ends having a contact; a movable assembly that moves between first and second positions, wherein the first position is a position in which each of the contacts of the first contact holders makes contact with one of the contacts of the movable end of one of the movable contact holders, and wherein the second position is a position in which the contacts of the first contact holders are separated from the contacts of the movable contact holders; an electromagnetic resetting component, which, when energized, causes the movable assembly to be in the first position; an electromagnetic tripping component, different from the electromagnetic resetting component, which, when energized, causes the movable assembly to be in the second position; and a control circuit, which, upon detection of a fault condition, energizes the electromagnetic tripping component, and which, after a reset switch is activated, energizes the electromagnetic resetting component.  
           [0013]    One particular object of an embodiment of the present invention is to provide a GFCI receptacle with reverse wiring protection that adopts an electromagnetic tripper and a corresponding control circuit.  
           [0014]    The GFCI receptacle according to an embodiment of the present invention comprises an electromagnetic tripper, a rear portion, a central body, a face portion, a test button, a reset button, an indicator, a mounting strap with a grounding strap and a binding screw, a pair of movable contact holders having one end fixed and the other end able to freely bias, a pair of fixed contact holders mounted on the central body, and a control circuit.  
           [0015]    Because the tripper is electromagnetic, the GFCI receptacle carries out the breaking and making operation through the interaction of the relevant electromagnetic force produced by the trip coil (J 1 ), the closing coil (J 2 ) produces, and the permanent magnet. Furthermore, by using the magnetic force of the permanent magnet to provide the retentivity of the tripper, the operating sensitivity is improved, and the GFCI is more energy efficient. According to another feature of the invention, the GFCI is provided with reverse wiring protection in that the control circuit is de-energized when the GFCI is miswired by connecting the line to the load, so that the GFCI receptacle can not be reset.  
           [0016]    A further object of an embodiment of the present invention is to provide an electromagnetic tripper that is electronically controlled. In such an embodiment (for example, the implementation shown in FIG. 10), the tripper comprises a permanent magnet, a coil framework, a trip coil, a closing coil, a plunger, a trip spring, a movable bracket, a balance frame, and a small spring providing a contact force for the movable contact holders. When the reset button is depressed, the closing coil will be energized and will produce an electromagnetic force that attracts with the magnetic force of the permanent magnet to act on the plunger to overcome the returning force of the trip spring and certain friction, thereby obtaining the goal that the tripper closes, and the magnetic force of the permanent magnet maintains the tripper in the closed condition. Because the plunger and the movable bracket are pressed together, the movement of the plunger directly drives the movable bracket to move along the same direction, and the movement of the movable bracket activates the balance frame to move. The movement of the balance frame lifts the removable contacts against the fixed contacts through the special shape of the movable contact holder (the removable contact has a V-shaped groove, and when it is in the tripping state, the bracket of the balance frame just locates in the V-shaped groove). When the tripper is in the closed state, the removable contact connects with the fixed contacts, and the small spring associated with the balance frame provides a contact force to maintain good contact all along, thereby maintaining the GFCI receptacle in the normal operating condition.  
           [0017]    When the GFCI receptacle of the above embodiment is energized, if there occurs a ground fault at the load or there is a factitious fault current, the control circuit will gate a silicon controlled rectifier (SCR) into conduction to energize the trip coil. The trip coil will then produce a electromagnetic force in the direction which repels the magnetic force of the permanent magnet. The electromagnetic force and the returning force of the trip spring act on the plunger, thereby making the tripper open quickly.  
           [0018]    Still another object of an embodiment of the present invention is to provide a special control circuit which mainly comprises the DC power, integrated amplification circuit, sensing circuit, trip circuit, reset circuit, and test circuit. In one embodiment of the invention in which these objects are satisfied, four diodes form a full-wave bridge rectifier circuit. After the AC is commutated by the rectifier circuit, there will be DC on the output terminal of the rectifier circuit. This embodiment includes an integrated amplification circuit, which may be a special IC (for example, of the type RV4145A or RV2145). The sensing circuit may include a sensor that comprises a sensing transformer and a neutral transformer. The AC line and neutral conductors pass through the transformers. In operation, the sensing transformer serves as a differential transformer for detecting a current leakage between the line side of the load terminal and an earth ground, while the neutral transformer detects current leakage between the neutral side of the load terminal and an earth ground. When an imbalance between the currents flowing in the line and neutral conductors of the AC supply is detected, a circuit breaker within the GFCI device is immediately tripped to an open condition, thereby opening both sides of the AC line and removing all power from the load. In the reset control circuit, the reset switch is connected to a silicon controlled rectifier (SCR). When the reset switch is closed, the SCR will be gated into conduction and will cause a closing coil connected with the SCR to be energized to thereby reset the GFCI. Simultaneously, a capacitor is connected to the reset switch to keep the closing coil energized for an instant. In this way, it prevents the closing coil from being burned out in the event that the current flowing through the closing coil is too large and the energized time is too long.  
           [0019]    The power supply of the control circuit is connected to the AC supply of the GFCI, so when the GFCI is energized, the control circuit is also energized. But, if the GFCI is miswired by connecting the line to the load, the control circuit is de-energized, and therefore, the GFCI will not be able to be reset, achieving the reverse wiring protection function. Because the reset of the GFCI is electronically controlled, the operation is more convenient and the action is more sensitive compared to GFCIs using mechanical means. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0020]    The invention will now be described in further detail in conjunction with the accompanying drawings, in which:  
         [0021]    [0021]FIG. 1 is a perspective view of a GFCI according to an embodiment of the present invention;  
         [0022]    [0022]FIG. 2 is a side view, in longitudinal section, of the GFCI in FIG. 1 showing the relative positions of the assembly in the trip condition;  
         [0023]    [0023]FIG. 3 is a perspective view of the GFCI in FIG. 1 with the face portion removed, showing the internal configuration of the GFCI of FIG. 1;  
         [0024]    [0024]FIG. 4 is an exploded, perspective view of the GFCI in FIG. 1;  
         [0025]    [0025]FIG. 5 is an exploded view of the electromagnetic tripper of the GFCI in FIG. 1;  
         [0026]    [0026]FIG. 6 is a perspective view of the trip actuator and a portion of the GFCI in FIG. 1, showing the assembled relation of the trip actuator;  
         [0027]    [0027]FIG. 7 is a detailed, sectional, side view of the GFCI in FIG. 1 in the trip condition;  
         [0028]    [0028]FIG. 8 is another detailed, sectional, side view of the GFCI in FIG. 1 in the trip condition, from a different perspective from FIG. 7;  
         [0029]    [0029]FIG. 9 is a detailed, sectional, side view of the GFCI in FIG. 1 in the closed condition; and  
         [0030]    [0030]FIG. 10 is a schematic diagram of a circuit of the GFCI according to an embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0031]    [0031]FIG. 1 shows a view of the exterior of a GFCI according to an embodiment of the present invention. The GFCI receptacle has a housing consisting of a face portion  30 , a central body  20  (not shown in FIG. 1, but appearing, for example, in FIG. 2) and a rear portion  10 . The face portion  30  has entry ports  31  for receiving normal or polarized prongs of a male plug of the type normally found at the end of a lamp or appliance cord set (not shown), as well as ground-prong-receiving openings  32  to accommodate three-wire plugs. The GFCI receptacle also includes a mounting strap  40  for fastening the receptacle to a junction box, and the mounting strap  40  has a threaded opening to receive a screw  113  for connection to an external ground wire. A test button  50  extends through an opening in the face portion  30  of the housing. The test button  50  can be activated to test the operation of the circuit-interrupting portion disposed in the device. A reset button  60 , which forms a part of a reset portion of the device, extends through an opening in the face portion  30  of the housing. The reset button is used to activate a reset operation, which reestablishes the electrical continuity in the open conductive paths. Electrical connections to existing household electrical wiring are made via binding screws  110  and  111 , where the binding screw  110  is a line phase connection, and the binding screw  111  is a load phase connection. It should be noted that two additional binding screws (not shown) are located on the opposite side of the GFCI receptacle. An indicator  114  (generally a light-emitting diode (LED)) extends through the opening of the face portion  30  of the housing. When the GFCI is normally energized, the indicator is illuminated.  
         [0032]    The GFCI illustrated in FIG. 1 may be rated, for example, at  20 A. The present invention also provides other types of GFCI, at various amperage ratings, and these GFCI receptacles all have two configurations, one without an indicator and the other with an indicator. Both configurations operate under the same principle. Therefore, the description below, while specifically for the rated  20 A GFCI with an indicator, the description also applies to the other types of GFCIs.  
         [0033]    Referring to FIG. 2, the assembled relation of the GFCI receptacle is shown in the trip condition. All of the subassemblies and component parts are fixed mainly to the housing (consisting of the face portion  30 , the central body  20  and the rear portion  10 ) of the GFCI. An electromagnetic tripper is set into the GFCI receptacle of the present invention. A permanent magnet  71  is set into one end of a coil framework  70 , and covered by a shield cover  72  outside. One end of the shield cover  72  is abutted against one side of the rear portion  10 . Shield cover  72  may be constructed of metal and may define a path of a magnetic field generated by at least one of the coils. The coil framework is mounted on a circuit board  90  by four binding pins. A circular core of sensor framework  80  is set into a fixed hole of the circuit board  90 , and the sensor framework  80  is also mounted on the circuit board  90  by four binding pins. The U-shaped portion of the sensor framework  80  is set into a corresponding groove on the central body  20 . There is an isolation layer  82  between the sensing transformer  81  and the neutral transformer  83 . The sensing transformer  81  may be composed, for example, of high original magneto-conductivity magnetic alloy flakes and enamel-insulated wire. The neutral transformer  83  may, for example, be composed of ferrite (high μ value, large temperature modulus) and enamel-insulated wire. A plunger  75  is molded into the side of a movable bracket  79 . The elasticity of a trip spring  76  makes one side of the movable bracket  79  abut against the sensor framework  80  in the trip condition. The upper side of the movable bracket  79  has a central hole, and a small spring  78  is set into it to prop up balance frame  77  and to provide a contact force for the contacts. Through the interaction of the magnetic force of the permanent magnet  71  and an electromagnetic force that the trip coil  74  or the closing coil  73  produces in an energized condition, the plunger  75  activates the movable bracket  79  to drive the balance frame  77  to move back and forth in the U-shaped groove, as shown. Contact strap  61  is molded into the underside of reset button  60 . One end of reset spring  62  props up the reset button  60 , and the other end presses onto mounting strap  40 . The test button  50  is propped up by test strap  51 . In one embodiment of the GFCI, this arrangement ensures that the top surface of the test button  50  is substantially level with the surface of the face portion  30 , until pressed.  
         [0034]    Referring to FIG. 3, a pair of fixed contact holders  100 A and  100 B with contacts  101  are mounted on the central body  20 . A mounting strap  40  with grounding strap  41  and binding screw  113  is set onto the central body  20 , and the face portion  30  impacts it. One end of a test strap  51  is set into a corresponding slot on the central body  20 , its outside abuts against the inside of the fixed contact holder  100 B, and the other end of the test strap  51  can flexibly contact with the test resistor  52  (shown, e.g., in FIG. 4). The contact strap  61 , which is molded into the underside of the reset button  60 , can flexibly contact the binding pins  63  through the action of the reset spring  62 , which props up the reset button  60 , thus, controlling the reset action of the tripper.  
         [0035]    [0035]FIGS. 2 and 3 also show the physical relationship among the mounting strap  40 , the central body  20 , and coil framework  70  (including both the trip coil  74  and the closing coil  73 ). In particular, these figures show that mounting strap  40  is physically separated from coil framework  70  by central body  20 . Central body  20  may be constructed of, for example, an insulating material. Central body  20  may thus be constructed such that mounting strap  40  does not define a path of a magnetic field generated by either trip coil  74  or closing coil  73 , i.e., such that mounting strap  40  is magnetically isolated from trip coil  74  and closing coil  73 .  
         [0036]    [0036]FIG. 4 is an exploded view of the GFCI receptacle according to an embodiment of the present invention. As shown, the GFCI receptacle comprises a rear portion  10 , a central body  20 , a face portion  30 , a mounting strap with a grounding strap  41  and a binding screw  113 , a pair of movable contact holders  102 A and  102 B with contacts  103 , a pair of fixed contact holders  100 A and  100 B with contacts  101 , an actuator, a reset mechanism, a test mechanism and a control circuit. The actuator comprises a coil framework  70 , a permanent magnet  71 , a shield cover  72 , a closing coil  73 , a trip coil  74 , a plunger  75 , a trip spring  76 , a balance frame  77 , a small spring  78  providing a contact force, a movable bracket  79 , and four binding pins  701 . The reset mechanism mainly comprises a reset button  60  molded with a contact strap  61  (shown in FIG. 3), a reset spring  62 , and a reset binding pin  63 . The test mechanism mainly comprises a test button  50 , a test strap  51 , a test resistor  52 , a sensor framework  80 , a sensing transformer  81 , an isolation layer  82 , and a neutral transformer  83 . In addition, the line terminal  104  is connected to the line wire by the line binding screw  110  associated with the pressure plate  105 ; the load can also be connected to the GFCI through the load binding screw  111  and a corresponding pressure plate  105 . All subassemblies and component parts are assembled as shown in the drawing. The rear portion and the face portion of the housing are connected together by four fastening screws  115 . The reset button  60  extends through the reset opening  33  on the face portion  30  of the housing. The test button  50  extends through the test opening  34  on the face portion  30  of the housing. One of the ends of each of the movable contact holders  102 A and  102 B passes through the sensor framework  80  and is soldered onto the circuit board  90 . The other end of each can move freely.  
         [0037]    [0037]FIG. 5 is an exploded view of the electromagnetic tripper of FIG. 4. Because the plunger  75  is molded onto the movable bracket  79 , the movement of the plunger  75  can drive the sliding boards  79 A and  79 B to move back and forth in the runners  70 A and  70 B, respectively. The movement of the movable bracket  79  drives the balance  77  to move to perform the operation of breaking and making. The assembled relation of the electromagnetic tripper is further shown in FIG. 6.  
         [0038]    Referring now to FIGS. 7, 8, and  9 , when the trip coil  74  or the closing coil  73  is energized, it produces a corresponding electromagnetic force to interact with the magnetic force of the permanent magnet  71  and acts on the plunger  75 . In this manner, the plunger  75  drives the balance frame  77  back and forth. In the trip condition, when trip coil  74  is energized, the bracket  77 A of the balance frame  77  is just set into the V-shaped groove A of the movable contact holder  102 A, and the bracket  77 B of the balance frame  77  is just set into the V-shaped groove B of the movable contact holder  102 B, as shown in FIGS. 7 and 8. As a result, the contacts  101  and  103  are separated from each other.  
         [0039]    On the other hand, when the closing coil  73  is energized, the plunger  75 , under the magnetic force drives the balance frame  77  to move such that the brackets  77 A and  77 B on the two sides of the balance frame  77  force the movable contact holders to bias. When one end of the plunger  75  is attracted to and pressed against the permanent magnet  71  (i.e., when closing coil  73  is energized), the brackets on two sides of the balance frame  77  are just located on the plane position of the V-shaped groove, and hold the contacts  103  of the movable contact holders against the contacts  101  of the fixed contact holders, as shown in FIG. 9. The small spring  78  provides a contact force for the contacts  103  and  101  to help maintain the contact. The special shape of the movable contact holders  102 A and  102 B prevents the plunger  75  from being attracted and closed in the event of improper operation, and also makes the tripper break quickly.  
         [0040]    [0040]FIG. 10 shows a general GFCI circuit of the present invention. Diodes D 1 -D 4  form a rectifying circuit, converting the AC input to a DC output. The junction of D 1  and D 2  and the junction of D 3  and D 4  form the AC input terminals and are connected to the line of the GFCI. The junction of D 2  and D 4  forms one terminal for the DC output, and this junction is referred to as the “ground” hereinafter. The junction of D 1  and D 3  forms the other terminal of the DC output and connects with the resistor R 4 . The other end of R 4  is connected to the capacitor C 5 . The other end of C 5  is then connected to the “ground”. In the exemplary 20A-rated GFCI device, an electrical voltage of approximately 26V formed between the two ends of C 5  serves as a DC voltage for the circuit.  
         [0041]    As discussed above, the exemplary ground fault circuit has a sensor, a trip circuit, a test circuit and a reset circuit. The sensor has a sensing transformer N 1  and a neutral transformer N 2 , as shown in FIG. 10. The AC line and the neutral conductors pass through both transformers. The two ends of a sensing coil of sensing transformer N 1  connect to opposite ends of the capacitor C 0 . One end of the sensing coil of N 1  serially connects to the capacitor C 1 , the resistor R 5 , and then the terminal  1  of the IC (which, as discussed below, may include an amplifier circuit), and the other end of the sensing coil of N 1  connects to the terminal  3  of the IC, forming a transformer-coupled circuit that receives differential voltage inputs. The feedback resistor, R 1 , connects to the terminal  1  of the IC at one end and to the terminal  7  of the IC at the other end. The magnitude of resistance at R 1  determines the amplification of the IC, that is, the threshold value for the tripping action of the GFCI.  
         [0042]    The neutral transformer N 2 , the capacitor C 2 , and the capacitor C 3  form the neutral ground-fault protection circuit. The two ends of the sensing coil of neutral transformer N 2  are connected to opposite ends of the capacitor C 2 . One end of the sensing coil of N 2  is further connected to the capacitor C 3  and the other end of the sensing coil of N 2  is connected to the “ground”. The other end of the capacitor C 3  is connected to the terminal  7  of the IC.  
         [0043]    Given the above-described apparatus, neutral ground-fault protection occurs as follows. The transformers N 1  and N 2  form a sigmoid-wave oscillator with a transformer-coupled oscillating frequency of 5 kHz. When neutral ground fault occurs, this oscillator starts to oscillate. When the magnitude of the oscillation reaches the IC threshold value, then the terminal  5  of the IC delivers a signal, putting the tripper in motion and the GFCI breaks.  
         [0044]    In other words, in operation, the sensing transformer (N 1 ) serves as a differential transformer for detecting a current leakage between the line side of the load terminal and an earth ground, while the neutral transformer (N 2 ) detects current leakage between the neutral side of the load terminal and an earth ground. In the absence of a ground fault condition, the currents flowing through the conductors will be equal and opposite, and no net flux will be generated in the core of the sensing transformer (N 1 ). In the event that a connection occurs between the line side of the load terminal and ground, however, the current flowing through the conductors will no longer precisely cancel and a net flux will be generated in the core of the sensing transformer (N 1 ). When the flux increases beyond a predetermined value, it will give rise to a potential at the output of the sensing transformer (N 1 ), which is applied to the inputs  1  and  3  of the IC and trip circuit, sufficient to produce a trip signal on the output terminal  5 . If the ground fault condition results from the neutral side of the load terminal being connected to ground, a magnetic path is established between the sensing transformer (N 1 ) and the neutral transformer (N 2 ). When this occurs, a positive feedback loop is created around an operational amplifier within the IC and trip circuit, and the resulting oscillations of the amplifier (IC) will likewise give rise to the trip signal on the output terminal  5 .  
         [0045]    As discussed above, resistor R 1  is utilized as a feedback resistor for setting the gain of the circuit and, hence, its sensitivity to ground faults. The capacitors C 1  and C 3  provide AC input coupling. In the absence of a ground fault condition, no output is produced by the amplifier (IC) and trip circuit on the output terminal  5 . Under these circumstances, the negative pole of a silicon controlled rectifier (SCR) VD 7  is connected to the ground of the full-wave bridge rectifier formed by D 1 -D 4  (described in detail above), and the positive pole of the SCR VD 7  is connected to trip coil J 1  to maintain it in a non-conducting state. Similarly, the negative pole of an SCR VD 5  is connected to the ground of the full-wave bridge rectifier, and the positive pole of the SCR VD 5  is connected to closing coil J 2  to maintain it in a non-conducting state. Since the current drawn by the resistor R 4  and amplifier and trip circuit is not sufficient to operate the trip coil, the plunger remains motionless.  
         [0046]    The occurrence of a ground fault condition causes the amplifier and trip circuit to produce an output on terminal  5  of the IC, which is applied to the gate terminal of the SCR VD 7 , thereby rendering the SCR VD 7  conductive. This produces a short circuit across the outputs of the full-wave bridge rectifier, thereby providing a low-impedance path for current to flow through the trip coil J 1 . The resulting movement of the plunger causes the movable contacts to move to the open position, thereby removing power from the entry ports of the face portion and the load terminals. This ensures that the GFCI receptacle remains in a condition to detect a ground fault condition immediately upon being reset.  
         [0047]    The reset switch RESET, the resistors R 2  and R 3 , the capacitors C 6  and C 7 , the SCR VD 5 , the closing coil J 2 , and the breaking switch K form the reset control circuit. One end of the reset switch RESET is connected to the junction of R 4  and C 5 , the other end of the reset switch RESET is connected to one junction of R 2  and C 6 , which are connected in parallel. The other junction of R 2  and C 6  is connected to the gate pole of the SCR VD 5 , R 3 , and C 7 . Capacitor C 7  is connected between the gate and cathode of the SCR VD 5  to serve as a filter for preventing narrow noise pulses from triggering the SCR VD 5 . One end of the breaking switch K is connected to the line terminal; the other end of K is connected to the load terminal. It is noted that the contact point between the breaking switch K and the line terminal corresponds to the contact  103  of the movable contact holder, and the contact point between the breaking switch K and the load terminal corresponds to the contact  101  of the fixed contact holder. The power supply of the control circuit is connected to the line of the GFCI, so when the GFCI is energized, the control circuit of the GFCI is also energized. When the reset switch RESET is closed, the capacitor C 6  is charged up, generating a trigger signal of about 20˜40 ms to gate the SCR VD 5  into conduction. Consequently the closing coil  73  is energized for a duration of about 20˜40 ms. That is, the closing coil  73  produces an electromagnetic force for about 20˜40 ms to act on the plunger  75 , sufficient to reset the GFCI.  
         [0048]    The IC may be a special integrated circuit, for example, of type RV4145A or RV2145.  
         [0049]    As discussed above, capacitor C 4  is connected between the gate and cathode of the SCR VD 7  to serve as a filter for preventing narrow noise pulses from triggering the SCR VD 7 . For additional protective purposes, the circuit shown in FIG. 10 also includes a metal oxide varistor (MOV) connected across the input terminals of the AC power source, in order to protect the whole control circuit from transient voltage surges.  
         [0050]    The test switch TEST and the current limiting resistor R 0  form the test circuit. The current limiting resistor Ro is connected to the power source, and the other end of resistor R 0  is connected to the test switch. The other end of the test switch TEST is connected to the other end of the load. The test circuit constantly provides the GFCI a 8 mA fault current for periodically checking of the working status of the GFCI. When the test switch is momentarily depressed, sufficient current will flow through the resistor R 0  to cause an imbalance in the current flowing through the sensing transformers. This will simulate a ground fault condition, causing the amplifier and trip circuit to produce an output signal on the output terminal  5  that gates the SCR VD 7  into conduction and thereby momentarily energizes the trip coil. The resulting movement of the plunger causes the contacts to open, as will occur during an actual ground fault condition.  
         [0051]    Simultaneously, the GFCI receptacle also provides an indication circuit, where a current limiting resistor R 6  is connected in series with a light-emitting diode (LED) VD 6 , and they are connected directly to the terminals of the load. When the reset button is depressed and the GFCI receptacle is energized, the LED is illuminated. This affords a visual indication to the installer and the user that the GFCI receptacle is in the normal conduction.  
         [0052]    If the GFCI receptacle is inadvertently miswired by connecting the line to the load, before the breaking switch K closes, the control circuit is de-energized. Because the GFCI utilizes an electro-controlled means for reset, when the control circuit is de-energized the closing coil can not be energized. In this manner, the closing coil can not produce a corresponding electromagnetic force to act on the plunger, thereby keeping the GFCI also de-energized, achieving the reverse wiring protection function.  
         [0053]    In summary, the present invention provides a GFCI receptacle that utilizes an electromagnetic tripper and an electro-controlled means to control reset. This GFCI receptacle has reverse wiring protection function and the advantages of tripping rapidly, operating conveniently, and reasonable configuration.  
         [0054]    While only the fundamental features of the present invention have been shown and described, it will be understood that various modifications and substitutions and changes of the form and details of the device described and illustrated and in its operation may be made by those skilled in the art, without departing from the spirit of the invention.