Patent Publication Number: US-2005117264-A1

Title: Ground fault circuit interrupter

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
      The present application claims the benefit under 35 U.S.C. 119(e) of U.S. provisional Patent Application Ser. No. 60/513,469, filed Oct. 22, 2003, the disclosure of which is incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION  
      The present invention relates generally to electrical safety devices and more particularly to ground fault circuit interrupters (GFCIs).  
      Alternating current (AC) power is typically delivered from a power source (e.g., a power plant) to a load (e.g., an electrical appliance plugged into a conventional electrical outlet) through a network of interconnected power cables, each power cable comprising a pair of conducting lines. Specifically, each power cable typically comprises a hot line (which is also commonly referred to in the art as a hot wire or a power line) and a neutral line (which is also commonly referred to in the art as a neutral wire).  
      The hot line is provided with a first end and a second end. The first end of the hot line (which is commonly referred to in the art as its line end) leads to a high energy source located at the power source. The second end of the hot line (which is commonly referred to in the art as its load end) leads to a load connected thereto.  
      Similarly, the neutral line is provided with a first end and a second end. The first end of the neutral line (which is commonly referred to in the art as its line end) leads to an electrically neutral source that is located at the power source. The second end of the neutral line (which is commonly referred to in the art as its load end) leads to the load connected thereto.  
      With the line end of each conductive line connected to a power source and with the load end of each conductive line connected to a load, a closed circuit is effectively created. Because the hot line connects to a high energy source and the neutral line connects to an electrically neutral source, a voltage is created across the circuit which, in turn, serves to power the load. When the closed circuit is operating properly, the current which flows through the hot line is equal to the current which flows through the neutral line.  
      However, it has been found that, on occasion, the hot line can connect directly to ground (e.g., if someone who is grounded accidentally touches the hot line). The connection of the hot line directly to ground causes the current flowing therethrough to drop, thereby establishing unequal current levels through the hot line and the neutral line. In response to the imbalance of currents flowing through the hot and neutral lines, the closed circuit will naturally adjust the current flow through the hot line to equal the current flow through the neutral line. This adjustment is accomplished through a rapid surge in the current level through the hot line (to a level which is equal to the current level through the neutral line). The resulting surge of electricity through the hot line (commonly referred to in the art as a ground fault condition) can potentially harm an individual who is operating the at the time of the current surge.  
      Accordingly, ground fault circuit interrupters are well known in the art and are widely used in commerce to protect against ground fault conditions (i.e., by opening the closed circuit). Examples of ground fault circuit interrupters are found in U.S. Pat. No. 6,052,266 to V. Aromin and U.S. Pat. No. 5,757,598 to V. Aromin, both of which are incorporated herein by reference.  
      One type of ground fault circuit interrupter (GFCI) which is well known in the art is provided with a pair of electrical outlets which can be used to power most types of conventional electrical appliances. This type of GFCI is typically installed directly into an electrical box which is, in turn, mounted within a bathroom or kitchen wall, this type of GFCI being commonly referred to as a wall mountable GFCI in the art. As such, wall mountable GFCIs serve two principal functions: (1) to provide a pair of electrical outlets for powering conventional electrical appliances (e.g., hair dryers, toasters, microwaves, etc.) and (2) to trip open the closed circuit upon detecting a ground fault condition in the power cable which, in turn, quickly terminates the flow of electricity (and, most importantly, the flow of any surge in current) into the load and both of the electrical outlets.  
      A ground fault circuit interrupter (GFCI) commonly includes a differential transformer with opposed primary windings, one primary winding being associated with the power line and the other primary winding being associated with the neutral line. If a ground fault condition should occur on the load side of the GFCI, the two primary windings will no longer cancel, thereby producing a flux flow in the core of the differential transformer. This resultant flux flow is detected by a secondary winding wrapped around the differential transformer core. In response thereto, the secondary winding produces a trip signal which, in turn, is used to open a switch located in at least one of the conducting lines between the power supply and the load (as well as between the power supply and the pair of electrical outlets), thereby eliminating the dangerous condition.  
      A ground fault circuit interrupter is traditionally constructed to include an exterior casing which is constructed out of a non-conductive material, such as plastic. Disposed within said casing is the ground fault circuit electronics (which are commonly mounted on a single double-sided printed circuit board). As noted above, a pair of electrical outlets are commonly integrated into the exterior casing and in electrical connection with the ground fault circuit electronics.  
      It should be noted that a plurality of conductive terminals are coupled to the ground fault circuit electronics and are externally accessible through small openings in the exterior casing, these conductive terminals serving as the point of connection for the GFCI to the power source and the load. In particular, the GFCI is provided with a pair of line side terminals, one of the terminals being designated for connection to the cable which leads to the hot line of the power source and the other terminal being designated for connection to the cable which leads to the neutral line of the power source. In addition, the GFCI is provided with a pair of load side terminals, one of the terminals being designated for connection to the cable which leads to the hot line of the load and the other terminal being designated for connection to the cable which leads to the neutral line of the load. Furthermore, the GFCI is often provided with a single grounding terminal (often marked in green to facilitate its identification) which is designated for connection to ground.  
      In U.S. Pat. No. 5,757,598, to V.V. Aromin, there is disclosed an example of a ground fault circuit interrupter (GFCI) which protects against ground fault conditions present in a power cord that extends between a source of power and a load. The GFCI includes a circuit breaker having a switch located in one of the pair of the lines. The switch has a first position in which the source of power in its associated line is not connected to the load and a second position in which the source of power in its associated line is connected to the load. A relay circuit is coupled to the switch for selectively positioning the switch in either the first or second position. The relay circuit includes a solenoid which operates in either an energized or a de-energized state. When energized, the solenoid positions the switch in its second position and when de-energized, the solenoid positions the switch in its first position. The GFCI also includes a booster circuit for selectively supplying a first voltage through the switch and to the solenoid which is sufficient to cause the solenoid to switch from its de-energized state to its energized state. A power supply circuit supplies a second voltage to the solenoid which is less than the first voltage. The second voltage is sufficient to maintain the solenoid in its energized state after being initially energized by the first voltage but is insufficient to switch the solenoid from its de-energized state to its energized state. A latch circuit operable in first and second bi-stable states allows the solenoid to switch from its de-energized state to its energized state and remain in its energized state when in its first bi-stable state and allowing solenoid to switch from its energized state to its de-energized state and remain in its de-energized state when in its second bi-stable state. A fault detection circuit detects the presence of a fault condition in at least one of the lines extending between the power and the load and causes the latch circuit to latch in its second bi-stable state upon detection of the fault condition.  
      While GFCIs of the type described above are well known in the art and widely used in commerce to protect electrical appliances from ground fault conditions, it has been found that these types of GFCIs suffer from a notable shortcoming.  
      Specifically, GFCIs of the type described above are typically designed to provide ground fault protection in only one direction (i.e., in the direction from terminals designated for connection to the power source to the terminals designated for connection to the load). As a result, GFCIs of the type described above are only capable of providing ground fault protection to its pair of electrical outlets as well as the load coupled thereto if the power source and load are connected to their designated terminals on the GFCI.  
      However, it has been found that, on occasion, consumers incorrectly connect the line and load side cables to the ground fault circuit interrupter. Specifically, consumers often inadvertently connect the cables leading to the power source (i.e., the line side cables) to the load side terminals on the GFCI and the cables leading to the load (i.e., the load side cables) to the line side terminals on the GFCI. This inadvertent mistake in the connection of the line and load side cables to the GFCI still serves to electrically connect the line to the load and, as a consequence, supply voltage to the load. In addition, this inadvertent mistake in connection still affords the load connected to the line side terminals of the GFCI with ground fault protection. However, this inadvertent mistake in connection precludes the electrical outlets which are integrated into the GFCI from providing ground fault protection. As a result of this common wiring mistake, a consumer who utilizes an electrical appliance that is plugged into one of the electrical outlets of the GFCI is rendered highly susceptible to the risk of a shock hazard, which is highly undesirable.  
      It is important to note that the consumer would not become aware of the aforementioned mistake in wiring because power would still be delivered to the load as well as to both electrical outlets. In addition, GFCIs which include test and reset buttons would function as if the GFCI were properly wired. As such, the user would believe that the GFCI is providing ground fault protection to the pair of electrical outlets when, in fact, no ground fault protection is actually being provided to the outlets.  
     SUMMARY OF THE INVENTION  
      It is an object of the present invention to provide a new and improved ground fault circuit interrupter (GFCI) which protects against ground fault conditions present in the hot and neutral lines of a power cable that connects a power source to a load.  
      It is another object of the present invention to provide a GFCI of the type described above which includes a first pair of conductive terminals which are designated for connection to the power source and a second pair of conductive terminals which are designated for connection to the load.  
      It is yet another object of the present invention to provide a GFCI of the type described above which includes a pair of electrical outlets.  
      It is yet another object of the present invention to provide a GFCI of the type described above which offers ground fault protection to the pair of electrical outlets in more than one direction.  
      It is yet another object of the present invention to provide a GFCI as described above which may be mass produced, has a minimal number of parts, and can be easily assembled.  
      Accordingly, in one embodiment of the present invention, there is provided a ground fault circuit interrupter (GFCI) for use with a power cable, the power cable being designed to connect a power source with a load, the power cable comprising at least a hot line and a neutral line, the ground fault circuit interrupter comprising a first pair of terminals located at one end of the power cable, a second pair of terminals located at the other end of the power cable, an electrical outlet connected to the power cable at a location between the first and second pairs of terminals, a first circuit breaker having a first switch, the first switch being located in one of the lines of the power cable between the first pair of terminals and the electrical outlet, the first switch having an open position and a closed position, a second circuit breaker having a second switch, the second switch being located in one of the lines of the power cable between the electrical outlet and the second pair of terminals, the second switch having an open position and a closed position, the first and second switches being ganged together, a relay circuit for selectively moving and maintaining each of the first and second switches in either its open position or its closed position, and a ground fault detection circuit for detecting the presence of a ground fault condition in the power cable between the first and second pairs of terminals, the ground fault detection circuit providing a trip signal upon detecting a ground fault condition in the power cable, the relay circuit moving and maintaining each of the first and second switches in its open position in response to the trip signal.  
      In another embodiment of the present invention, there is provided a ground fault circuit interrupter (GFCI) for use with a power cable, the power cable being designed to connect a power source with a load, the power cable comprising at least a hot line and a neutral line, the ground fault circuit interrupter comprising a first pair of terminals located at one end of the power cable, the first pair of terminals being designated for connection to the power source, a second pair of terminals located at the other end of the power cable, the second pair of terminals being designated for connection to the load, an electrical outlet connected to the power cable at a location between the first and second pairs of terminals, a circuit breaker having a first switch, the first switch being located in one of the lines of the power cable between the first pair of terminals and the electrical outlet, the first switch having an open position and a closed position, a relay circuit for selectively moving and maintaining the first switch in either its open position or its closed position, a reverse wiring circuit for generating an artificial ground fault condition when the power source is connected to the second pair of terminals, and a ground fault detection circuit for detecting the presence of either a ground fault condition in the power cable between the first and second pairs of terminals or an artificial ground fault condition generated by the reverse wiring circuit, the ground fault detection circuit providing a trip signal upon detecting either the ground fault condition or the artificial ground fault condition, the relay circuit moving and maintaining the first switch in its open position in response to the trip signal.  
      Additional objects, as well as features and advantages, of the present invention will be set forth in part in the description which follows, and in part will be obvious from the description or may be learned by practice of the invention. In the description, reference is made to the accompanying drawings which form a part thereof and in which is shown by way of illustration specific embodiments for practicing the invention. These embodiments will be described in sufficient detail to enable those skilled in the art to practice the invention, and it is to be understood that other embodiments may be utilized and that structural changes may be made without departing from the scope of the invention. The following detailed description is, therefore, not to be taken in a limiting sense, and the scope of the present invention is best defined by the appended claims.  
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      The accompanying drawings, which are hereby incorporated into and constitute a part of this specification, illustrate various embodiments of the invention and, together with the description, serve to explain the principles of the invention. In the drawings wherein like reference numerals represent like parts:  
       FIG. 1  is a front plan view of a prior art ground fault circuit interrupter;  
       FIG. 2  is a rear plan view of the prior art ground fault circuit interrupter which is shown in  FIG. 1 ;  
       FIG. 3  is an electrical schematic of the prior art ground fault circuit interrupter which is shown in  FIG. 1 ;  
       FIG. 4  is a first embodiment of a ground fault circuit interrupter constructed according to the teachings of the present invention;  
       FIG. 5  is a second embodiment of a ground fault circuit interrupter constructed according to the teachings of the present invention; and  
       FIG. 6  is a third embodiment of a ground fault circuit interrupter constructed according to the teachings of the present invention.  
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS  
      Referring now to  FIGS. 1-3 , there is shown a prior art ground fault circuit interrupter (GFCI) which is identified generally by reference numeral  11 . GFCI  11  is designed principally for use as a safety device for a power cable P (also referred to herein as a power cord) which connects a line (also referred to herein as a power source) to a load (e.g., an electric appliance), the power cable P comprising a hot line H, a neutral line N and a ground line G. As will be described further below, prior art GFCI  11  provides protection against ground fault conditions present in the power cable.  
      GFCI  11  is provided with an exterior casing  13  which is constructed out of a non-conductive material such as plastic. Casing  13  has a generally box-shaped design and includes a flat front surface  15 , a flat rear surface  17 , a top surface  19 , a bottom surface  21 , a right side surface  23  and a left side surface  25 . Casing  13  is preferably constructed out of two separately molded pieces which are then secured together (e.g., through a snap-fit interconnection) during a subsequent manufacturing process.  
      GFCI  11  includes a pair of metal brackets  27 , one bracket  27 - 1  extending at an approximate right angle relative to top surface  19  and the other bracket  27 - 2  extending at an approximate right angle relative to bottom surface  21 . Together, brackets  27  enable GFCI  11  to be installed into a conventional electrical box which, in turn, is fixedly disposed within a bathroom or kitchen wall. For this reason, GFCI  11  is commonly referred to as a wall mountable ground fault circuit interrupter in the art.  
      As seen most clearly in  FIG. 1 , front surface  15  at least partially defines a pair of standard electrical outlets  29 , wherein a top outlet  29 - 1  is positioned directly above a bottom outlet  29 - 2 . It should be noted that a plurality of differently shaped openings  31 - 1 ,  31 - 2  and  31 - 3  are formed in front surface  15 , each opening  31  providing access to a corresponding conductive terminal for outlet  29 , as will be described further below.  
      An externally accessible test button  33  and an externally accessible reset button  35  project through corresponding openings formed in front surface  15 . Buttons  33  and  35  are coupled to associated switches which are located inside casing  13  (as will be described further below) and can be used to perform selected operations for GFCI  11 .  
      A plurality of externally accessible conductive terminals  37 ,  39  and  41  are provided which serve as connection points for coupling the power source, load and ground to GFCI  11 . Terminals  37 ,  39  and  41  are coupled, at one end, to the GFCI electronics (shown in schematic form in  FIG. 3 ) which are located within casing  13 , the free end of each terminal  37 ,  39  and  41  extending out through a corresponding opening in casing  13  so as to render it externally accessible for connection thereto.  
      It should be noted that each of conductive terminals  37 ,  39  and  41  is represented herein as being in the form of a threaded metal screw which can be driven inward (e.g., using a screwdriver) to draw a conductive lead, or wire, into electrical contact against a metallic plate (not shown). However, it is to be understood that various alternative types of connection means (e.g., push-in wire receptacles) are commonly utilized to connect a GFCI to a load, line and/or ground.  
      As seen most clearly in  FIG. 2 , conductive terminals  37  are designated as the line side terminals for GFCI  11 . Specifically, conductive terminal  37 - 1  is designated for connection to the wire which leads to the hot line H of the power source. In addition, conductive terminal  37 - 2  is designated for connection to the wire which leads to the neutral line N of the power source. It should be noted that each of line side terminals  37  is identified on rear surface  17  to ensure proper connection thereto.  
      Conductive terminals  39  are designated as the load side terminals for GFCI  11 . Specifically, conductive terminal  39 - 1  is designated for connection to the wire which leads to the hot line H of the load. In addition, conductive terminal  39 - 2  is designated for connection to the wire which leads to the neutral line N of the load. It should be noted that each of load side terminals  39  is identified on rear surface  17  to ensure proper connection thereto.  
      Conductive terminal  41  is designated as the ground terminal for GFCI  11 . Specifically, conductive terminal  41  is designated for connection to the wire which leads to ground. It should be noted that, in order to ensure the proper connection to ground, conductive terminal  41  is often colored green (which is recognized in the industry as representing a ground connection) and rear surface  17  of casing  13  is also provided with a suitable identifying marker.  
      Referring now to  FIG. 3 , there is shown a simplified circuit diagram of GFCI  11 . In this circuit diagram, GFCI  11  connects a load (identified in  FIG. 3  as LOAD) to a power source (identified in  FIG. 3  as LINE) through a hot line H, a neutral line N and a ground line G. In addition, GFCI  11  connects electrical outlets  29 - 1  and  29 - 2  to the power source through hot line H, neutral line N and ground line G. As will be described further below, GFCI  11  is provided with means for suspending the application of power from the power source to both the load and outlets  29  upon sensing the presence of a ground fault condition along lines H and N. It should be noted that the majority of the electrical components shown in  FIG. 3  are housed within the interior of casing  13  and are mounted on a common double-sided printed circuit board (not shown).  
      GFCI  11  includes a circuit breaker  43  for controlling the delivery of power along conductive lines H and N from the power source to both the load and outlets  29 , a relay circuit  45  for controlling the operation of the circuit breaker  43 , a power supply circuit  47  for supplying power to selected electrical components in GFCI  11 , a fault detection circuit  49  for sensing the presence of a ground fault condition in hot and neutral lines H and N, a latch circuit  51  for converting a fault condition signal produced by fault detection circuit  49  into the appropriate signal which can be used to regulate relay circuit  45 , and a test circuit  53  for verifying that GFCI  11  is operating properly.  
      Circuit breaker  43  includes a pair of normally closed, single-pole, single-throw switches K 1  and K 2  which are located in hot and neutral conductive lines H and N, respectively, between the power source and the load (as well as between the power source and outlets  29 ). Switches K 1  and K 2  can be disposed in either of two positions: a first position in which switches K 1  and K 2  are open (as illustrated in  FIG. 3 ), such that the supply of AC power is suspended from the power source to the load (as well as outlets  29 ); and a second position in which switches K 1  and K 2  are both closed, such that the supply of AC power from the power source is delivered to the load (as well as outlets  29 ).  
      Relay circuit  45  is responsible for controlling the connective position of switches K 1  and K 2 . Specifically, relay circuit  45  includes a solenoid SOL that is ganged to the circuit breaker contacts of switches K 1  and K 2 . Before power is applied to GFCI  11 , solenoid SOL positions switches K 1  and K 2  in their second connective position (i.e., their closed positions). After power is applied to GFCI  11 , solenoid SOL will retain switches K 1  and K 2  in their second connective positions (i.e., their closed positions). However, once solenoid SOL is energized, solenoid SOL moves switches to their first connective positions (i.e., their open positions).  
      Power supply circuit  47  supplies power to selected components in GFCI  11 . Power supply circuit  47  comprises a metal oxide varistor MOV, four silicon controlled rectifiers D 1 , D 2 , D 3  and D 4 , a voltage dropping resistor R DROP , and a storage capacitor C STORAGE . Varistor MOV helps to protect the load against a voltage surge from the AC power source. Rectifiers D 1 -D 4  (each having a model number of 1N4004) together form a conventional diode rectifier bridge and serve to convert the alternating current (AC) power from the power source into direct current (DC) power. Voltage dropping resistor R DROP  has a value of 24 Kohms and acts to limit the input voltage to solenoid SOL to prevent inadvertent switching in circuit breaker  43 . Storage capacitor C STORAGE  has a value of 0.01 uF and acts to charge to full line potential when reset button  35  is depressed.  
      Fault detection circuit  49  acts to detect the presence of ground fault conditions in conductive lines H and N when switches are disposed in their second connective position (i.e., their closed positions). Fault detection circuit  49  comprises a sense transformer T 1 , a grounded neutral transformer T 2 , a coupling capacitor C COUPLING , a noise suppression capacitor C NOISE , a tuning capacitor C TUNE , a sense resistor R SENSE  and a ground fault interrupter chip U 1 . Sense transformer T 1  senses the current differential between the hot and neutral conductive lines H and N, and upon the presence of a ground fault condition, transformer T 1  induces an associated output from its secondary windings. Grounded neutral transformer T 2  acts in conjunction with transformer T 1  to sense the presence of grounded neutral conditions and, in turn, induce an associated output. Coupling capacitor C COUPLING  has a value of 10 uF and acts to couple the alternating current signal from the secondary winding of sense transformer T 1  to chip U 1 . Noise suppression capacitor C NOISE  has a value of 0.01 uF and acts to prevent fault detection circuit  49  from operating in response to line disturbances such as electrical noise and lower level faults. Tuning capacitor C TUNE  has a value of 0.03 uF and sense resistor R SENSE  has a value of 1.0 Mohms. Together tuning capacitor C TUNE  and sense resistor R SENSE  act to set the minimum fault current at which fault detection circuit  49  provides an output signal to latch circuit  51 . Interrupter chip U 1  is an RV4145 low power ground fault interrupter circuit which is sold by Raytheon Corporation. Chip U 1  serves to amplify the fault signal generated by sense transformer T 1  and provide an output, or trigger, pulse (at pin  5 ) to activate latch circuit  51 .  
      Latch circuit  51  acts to take the electrical signal produced by fault detection circuit  49  (i.e., at output pin  5 ) upon the detection of a ground fault condition and, in turn, energize solenoid SOL. Latch circuit  51  comprises a silicon controlled rectifier SCR which is operable in either a conductive or non-conductive state and a filter capacitor C FILTER . Preferably, reset switch  35  is provided as part of latch circuit  51  and is connected at one end to the anode of rectifier SCR and at the other end to the cathode of rectifier SCR (although reset switch  35  is not shown in the schematic shown in  FIG. 3 ). Rectifier SCR is an EC103D rectifier sold by Teccor Corporation and acts to selectively control the state of solenoid SOL. Filter capacitor C FILTER  has a value of 2.2 uF and acts in preventing rectifier SCR from producing a signal as a result of electrical noise in GFCI  11 .  
      Test circuit  53  provides a means of testing whether GFCI  11  is operating properly. Test circuit  53  comprises a current limiting resistor R TEST  having a value of 15 Kohms and test switch  33  (which is of the conventional push-in type design). When test switch  33  is depressed to energize test circuit  53 , resistor R TEST  provides a simulated fault current to sense transformer T 1  which is similar to a ground fault condition.  
      Outlets  29 - 1  and  29 - 2  are connected to hot and neutral conductive lines H and N at a location between circuit breaker  43  and load-side terminals  39 . Specifically, each outlet  29  includes a neutral line conductive terminal  55  which is connected to neutral line N at a location between terminal  39 - 2  and switch K 2 , each conductive terminal  55  being externally accessible through a corresponding opening  31 - 1  in casing  13 . Similarly, each outlet  29  includes a hot line conductive terminal  57  which is connected to hot line H at a location between terminal  39 - 1  and switch K 1 , each conductive terminal  57  being externally accessible through a corresponding opening  31 - 2  in casing  13 . Furthermore, each outlet  29  includes a ground terminal  59  which is connected to ground G, each ground terminal  59  being externally accessible through a corresponding opening  31 - 3  in casing  13 .  
      As noted above, GFCI  11  connects a power source (represented as LINE in  FIG. 3 ) to both a load (represented as LOAD in  FIG. 3 ) and electrical outlets  29  through a plurality of conductive lines (represented as H, N and G in  FIG. 3 ) and, in addition, provides both the load and outlets  29  with protection against ground fault conditions that are present along the conductive lines. It is essential to note that GFCI  11  is constructed with line side terminals  37  designated to receive the power source and load side terminals  39  designated to receive the load.  
      With the power source connected to line side terminals  37  and the load connected to load side terminals  39 , GFCI  11  operates in the following manner. In the absence of a ground fault condition, switches K 1  and K 2  are disposed in their closed positions, thereby enabling AC power to pass from the power source (i.e., LINE) to both the load and outlets  29  through hot and neutral conductive lines H and N.  
      As alternating current (AC) power is being supplied from the power source to the load and outlets  29 , fault detection circuit  49  monitors the conductive lines for the presence of a ground fault condition (i.e., unequal current values along hot and neutral lines H and N). If a ground fault condition is detected along the conductive lines (or upon the depression of test button  33 ), fault detection circuit  49  sends a signal to latch circuit  51  which, in turn, energizes solenoid SOL. The activation of solenoid SOL causes switches K 1  and K 2  (which are ganged together to solenoid SOL) to open. With switches K 1  and K 2  open, the potentially dangerous ground fault condition present along hot and neutral lines H and N (in particular, between line side terminals  37  and circuit breaker  43 ) is unable to pass onto the load or electrical outlets  29 . In this manner, the load as well as outlets  29  are protected against receiving the ground fault condition from the power source, which is highly desirable. Once the fault condition is eliminated, GFCI  11  can be reset through the depression of reset button  35  which, in turn, causes solenoid SOL to return switches K 1  and K 2  to their closed positions.  
      Although rear surface  17  of casing  13  is provided with markings to facilitate proper connection, it has nonetheless be found that, on occasion, consumers incorrectly connect the power source and load to the GFCI  11 . Specifically, consumers often inadvertently connect the cables leading to the power source (i.e., the line side cables) to load side terminals  39  and the cables leading to the load (i.e., the load side cables) to line side terminals  37 . This inadvertent wiring mistake still enables the power source to supply voltage to both the load and outlets  29  through conductive lines H and N when switches K 1  and K 2  are in their closed positions. In addition, this inadvertent wiring mistake does not compromise the ability of GFCI  11  to provide the load with ground fault protection. However, with the power source and load coupled to GFCI  11  in this manner, it should be noted that outlets  29  are not provided with ground fault protection, which is highly undesirable.  
      Specifically, power is supplied from the power source via load side terminals  39  to the load via line side terminals  37 . The power supplied by the power source travels through circuit breaker  43  and is ultimately measured by fault detection circuit  49 . When a ground fault condition is detected along conductive lines H and N by fault detection circuit  49 , solenoid SOL opens switches K 1  and K 2  of circuit breaker  43 , thereby suspending further application of power from the power source to the load.  
      However, it should be noted that opening switches K 1  and K 2  does not serve to protect electrical outlets  29  from the ground fault condition in the conductive lines. Rather, with switches K 1  and K 2  open, any ground fault condition in the conductive lines that is derived from the power source will still pass into outlets  29 . As a result, even though switches K 1  and K 2  have been opened in response to the detection of a ground fault condition, a closed circuit remains between outlets  29  and the power source and, accordingly, any current imbalance (as well as any resulting current surge) present along the conductive lines at the power source will flow into outlets  29 . Accordingly, any electrical appliance which in is connected to outlets  29  remains susceptible to potentially dangerous electrical shock conditions, which is highly undesirable.  
      It is important to note that, with the load and power source improperly wired to GFCI  11  as set forth above, the consumer would be unaware of the lack of ground fault protection being provided to outlets  29 . Specifically, in the absence of a ground fault condition, the load and outlets  29  would receive power from the power source as if the connections were proper. In addition, test button  33  and reset button  35  would operate as if GFCI  11  were properly wired. As a result, a consumer may power an electrical appliance through outlets  29  with the understanding that the appliance is being provided with ground fault protection when, in fact, GFCI  11  is providing no ground fault protection to the appliance.  
      It is for the reasons enumerated above that prior art GFCI  11  is identified herein as providing ground fault protection in only one direction. Specifically, GFCI  11  provides ground fault protection to outlets  29  in only the direction from line side terminals  37  to load side terminals  39 . However, GFCI  11  does not provide ground fault protection to outlets  29  in the opposite direction (i.e., in the direction from load side terminals  39  to line side terminals  37 ), which is highly undesirable.  
      Accordingly, referring now to  FIG. 4 , there is shown a first embodiment of a ground fault circuit interrupter (GFCI) which is constructed according to the teachings of the present invention, the GFCI being identified generally by reference numeral  111 . As will be described further below, GFCI  111  differs from prior art GFCI  11  in that GFCI  111  provides ground fault protection to outlets  29  in two directions (i.e., in either direction between terminals  37  and  39 ) whereas prior art GFCI  11  provides ground fault protection to outlets  29  in only one direction (i.e., in the direction from terminals  37  to terminals  39 ).  
      GFCI  111  is identical in all respects with GFCI  11  with two notable distinctions.  
      As a first notable distinction of GFCI  111  in view of GFCI  11 , it should be noted that GFCI  111  includes a second circuit breaker  113  for controlling the delivery of power along conductive lines H and N from the power source to the load. Circuit breaker  113  includes a pair of normally closed, single-pole, single-throw switches K 3  and K 4  which are located in hot and neutral conductive lines H and N, respectively, between line side terminals  37  and circuit breaker  43 , with circuit breaker  43  located in hot and neutral conductive lines H and N, respectively between circuit breaker  113  and load side terminals  39 . Switches K 1 , K 2 , K 3  and K 4  are all ganged together to solenoid SOL. As a result, with solenoid SOL deactivated, switches K 1 , K 2 , K 3  and K 4  are all disposed in their closed positions. To the contrary, with solenoid SOL activated, switches K 1 , K 2 , K 3  and K 4  are all disposed in their open positions.  
      As a second notable distinction of GFCI  111  in view of GFCI  11 , it should be noted that outlets  29  in GFCI  111  are connected to conductive lines H and N of the power cord at a location between circuit breaker  43  and circuit breaker  113  (whereas outlets  29  in GFCI  11  are connected to conductive lines H and N at a location between circuit breaker  43  and load side terminals  39 ). Specifically, each outlet  29  includes a neutral line conductive terminal  55  which is connected to neutral line N at a location between circuit breakers  43  and  113  and a hot line conductive terminal  57  which is connected to hot line H at a location between circuit breakers  43  and  113 .  
      As can be appreciated, the two distinctions noted above provide GFCI  111  with the ability to protect outlets  29  from ground fault conditions in either of two directions (i.e., regardless of whether the power source is connected to line side terminals  37  or load side terminals  39 ). Specifically, with the power source connected to line side terminals  37  and the load connected to load side terminals  39  (i.e., in the proper manner as designated), GFCI  111  operates in the following manner. In the absence of a ground fault condition, switches K 1 , K 2 , K 3  and K 4  are all closed, thereby enabling AC power to pass from the power source to both outlets  29  and the load. If a ground fault condition is detected along the conductive lines, solenoid SOL opens switches K 1 , K 2 , K 3  and K 4 . With switches K 1  and K 2  open, the load is electrically disconnected from the power source and, as a consequence, the ground fault condition. Further, with switches K 3  and K 4  open, outlets  29  are electrically disconnected from the power source and, as a consequence, the ground fault condition. In this manner, GFCI  111  protects both the load and outlets  29  from the ground fault condition, which is highly desirable.  
      With the power source connected to load side terminals  39  and the load connected to line side terminals  37  (i.e., in the reverse manner as designated), GFCI  111  operates in the following manner. In the absence of a ground fault condition, switches K 1 , K 2 , K 3  and K 4  are all closed, thereby enabling AC power to pass from the power source (located at load side terminals  39 ) to both the load (located at line side terminals  37 ) and outlets  29 . If a ground fault condition is detected along the conductive lines, solenoid SOL opens switches K 1 , K 2 , K 3  and K 4 . With switches K 3  and K 4  open, the load is electrically disconnected from the power source and, as a consequence, the ground fault condition. Further, with switches K 1  and K 2  open, outlets  29  are electrically disconnected from the power source and, as a consequence, the ground fault condition. In this manner, GFCI  111  protects both the load and outlets  29  from the ground fault condition in two directions, which is a principal object of the present invention.  
      It should be noted that the bi-directional ground fault protection afforded to outlets  29  (as well as the load) by GFCI  111  means that it is no longer necessary for terminals  37  and  39  to be designated for a particular connection (e.g., to the load or power source). As a result, the consumer is afforded greater flexibility during the connection process, which is highly desirable.  
      Referring now to  FIG. 5 , there is shown a second embodiment of a ground fault circuit interrupter (GFCI) which is constructed according to the teachings of the present invention, the GFCI being identified generally by reference numeral  211 . As will be described further below, GFCI  211  differs from prior art GFCI  11  in that GFCI  211  provides ground fault protection to outlets  29  in two directions (i.e., in either direction between terminals  37  and  39 ) whereas prior art GFCI  11  provides ground fault protection to outlets  29  in only one direction (i.e., in the direction from terminals  37  to terminals  39 ).  
      GFCI  211  is identical in all respects with GFCI  11  with two notable distinctions.  
      As a first notable distinction of GFCI  211  in view of GFCI  11 , it should be noted that outlets  29  in GFCI  211  are connected to conductive lines H and N of the power cord at a location between circuit breaker  43  and line side terminals  37  (whereas outlets  29  in GFCI  11  are connected to conductive lines H and N at a location between circuit breaker  43  and load side terminals  39 ). Specifically, each outlet  29  includes a neutral line conductive terminal  55  which is connected to neutral line N at a location between switch K 2  and line side terminal  37 - 2  and a hot line conductive terminal  57  which is connected to hot line H at a location between switch K 1  and line side terminal  37 - 1 .  
      As a second notable distinction of GFCI  211  in view of GFCI  11 , it should be noted that GFCI  211  includes a reverse wiring circuit  213  for generating an artificial ground fault condition (which, in turn, trips GFCI  211 ) when the power source and the load are connected to GFCI  211  in the reverse order, as will be described further below. Reverse wiring circuit  213  includes a reverse wiring resistor R REV  (having a value preferably in the range of 68470 ohms). Reverse wiring resistor R REV  extends through sense transformer T 1  and is connected at one end to test circuit  53  and is connected at its other end to load side terminal  39 - 1 .  
      As can be appreciated, the two distinctions noted above provide GFCI  211  with the ability to protect outlets  29  from ground fault conditions in either of two directions (i.e., regardless of whether the power source is connected to line side terminals  37  or load side terminals  39 ). With the power source connected to line side terminals  37  and the load connected to load side terminals  39  (i.e., in the proper manner as designated), GFCI  211  operates in a similar manner as GFCI  11 . Specifically, in the absence of a ground fault condition, switches K 1  and K 2  remain closed, thereby enabling AC power to pass from the power source to both the load (at load side terminals  39 ) and outlets  29 . It should be noted that test switch  33  is normally open, thereby precluding reverse wiring resistor R REV  from producing a signal that can be detected by sense transformer T 1  as an artificial ground fault condition. If a true ground fault condition is detected along the conductive lines of the power cord, solenoid SOL opens switches K 1  and K 2 . With switches K 1  and K 2  open, the load as well as outlets  29  are electrically disconnected from the power source and, as a consequence, the ground fault condition. In this manner, GFCI  211  protects both the load and outlets  29  from the ground fault condition, which is highly desirable.  
      However, it should be noted that GFCI  211  operates differently than GFCI  11  when the power source is connected to load side terminals  39  and the load is connected to line side terminals  37  (i.e., in the reverse manner as designated). Specifically, by wiring the power source to load side terminals  39 , a current is supplied directly into reverse wiring resistor R REV  which, in turn, causes sense transformer T 1  to detect the presence of a current imbalance in the conductive lines. In response thereto, solenoid SOL opens switches K 1  and K 2 . With switches K 1  and K 2  open, the load and outlets  29  are electrically disconnected from the power source and, as a result, any appliance connected thereto will not receive power. In this sense, the current which passes through reverse wiring resistor R REV  acts as an artificial fault condition which, in turn, suspends the application of power from the power source to both the load and outlets  29 . With GFCI  211  tripped open upon the detection of this artificial fault condition, it is to be understood that any future depression of reset button  35  will immediately cause reverse wiring circuit  213  to generate another artificial signal to trip open GFCI  211  once again. In fact, GFCI  211  will continue to trip open every time reset button  35  is depressed. As a result, the load and outlets  29  will never be supplied the unprotected power from the power source until the connection of GFCI  211  to the power source and the load are made proper.  
      It should be noted that, if GFCI  211  is wired properly, the first application of power through hot and neutral conductive lines H and N will ultimately travel through reverse wiring resistor R REV . Due to the relatively small resistance of reverse wiring resistor R REV  (i.e., in the range of approximately 68-470 ohms), the reverse wiring resistor R REV  will instantly overheat and burn out upon the first application of power through the hot and neutral line terminals. Once the reverse wiring resistor R REV  burns out, that portion of the circuit is rendered inoperable and GFCI  211  operates normally as described in detail above.  
      Referring now to  FIG. 6 , there is shown a third embodiment of a ground fault circuit interrupter (GFCI) which is constructed according to the teachings of the present invention, the GFCI being identified generally by reference numeral  311 . As can be appreciated, GFCI  311  operates in a similar manner as GFCI  211 . As such, it is to be understood that GFCI  311  functions by (1) providing ground fault protection to outlets  29  when the power source and load are connected to GFCI  311  in a proper manner and (2) maintaining GFCI  311  in a tripped condition (i.e., suspending the application of power from the line to the load and outlets  29 ) when the power source and load are connected to GFCI  311  in the reverse order.  
      The sole distinction between GFCI  311  and GFCI  211  relates to the fact that GFCI  311  includes a reverse wiring circuit  313  which differs slightly in construction from reverse wiring circuit  213  in GFCI  211 . Specifically, reverse wiring circuit  313  is similar to reverse wiring circuit  213  in that reverse wiring circuit  313  includes a reverse wiring resistor R REV  which extends through sense transformer T 1  and is connected at one end to test circuit  53  and is connected at its other end to load side terminal  39 - 1 . However, reverse wiring circuit  313  differs from reverse wiring circuit  213  in that reverse wiring circuit  313  additionally includes a fuse  315  which is connected in series with reverse wiring resistor R REV . It is to be understood that fuse  315  is provided in reverse wiring circuit  313  to facilitate the opening (i.e., burning out) process of reverse wiring circuit  313  when GFCI  311  is wired properly.  
      The versions of the present invention described above are intended to be merely exemplary and those skilled in the art shall be able to make numerous variations and modifications to it without departing from the spirit of the present invention. For example, although the majority of the fireguard circuits described in detail above are shown for use as a safety device for a power cable which comprises three conducting lines, it is to be understood that these fireguard circuits could also be used as a safety device for a power cable which comprises two conducting lines without departing from the spirit of the present invention. All such variations and modifications are intended to be within the scope of the present invention as defined in the appended claims. For example, it should be noted that the particular components which make up the aforementioned embodiments may be interchanged or combined to form additional embodiments.