Abstract:
An apparatus and method for making fault interrupter receptacles tolerant to miswiring errors. By employing redundant sense elements plus a special switch configuration, the device obtains a symmetry that makes it unnecessary to designate specific line and load terminals. The addition of open neutral protection, ground assurance, transposed conductor protection and end-of-life protection provides enhanced performance with the addition of only a few parts relative to a conventional fault protection unit.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   This application is a continuation-in-part application of U.S. patent application Ser. No. 10/237,319, entitled “Fail Safe Fault Interrupter Using Secondary Breaker,” filed on Sep. 8, 2002 now U.S. Pat. No. 6,831,819, and claiming the priority date of U.S. Provisional Patent Application Ser. No. 60/322,368, filed on Sep. 9, 2001. This application also claims priority to U.S. Provisional Patent Application Ser. No. 60/516,015, entitled “Fault Interrupter with Interchangeable Line Load Connections,” filed on Oct. 30, 2003. The specifications of the above applications are incorporated herein by reference. 

   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   This invention relates to a fault interruption device that is configured for wall receptacle applications. By utilizing a special switch configuration, the fault interruption device may be installed with swapped line and load terminals with no loss of protection to local and remote outlets. Ground assurance, open neutral detection and line reversal detection are easily incorporated along with a self testing capacity, enabling a versatile, low cost fault interrupter that presents a high degree of protection against wiring conditions that may compromise safety. 
   2. Background of the Invention 
   Ground fault current interrupters (GFCIs) are devices that are often used in load centers and in receptacle outlets in commercial and residential buildings. These devices protect against undesirable electrical leakages to earth ground by sensing current imbalances in the power delivery conductors and interrupting power delivery upon the occurrence of a possibly hazardous leakage condition. Another type of device, called an arc fault current interrupter (AFCI), is used to detect high energy discharges between electrified objects in a distribution network or from one electrified object to ground. Both GFCIs and AFCIs are required by code to be installed in particular locations in dwellings and commercial construction and both devices are occasionally co-located. Although AFCIs and GFCIs protect against different types of events, they have a similar construction and encounter similar problems and the present patent will refer to both types of devices as fault interrupters. 
   A malfunctioning fault interrupter will not provide protection. Malfunctions may occur due to two broad categories of source: defect or incorrect installation. First, a malfunction may occur due to a defect in design or performance of the fault interrupter or to the malfunction of one or more constituent components. Second, a malfunction may occur if the fault interrupter is incorrectly installed or if required electrical connections to the fault interrupter become loose or are damaged. 
   In the U.S., electrical distribution networks generally provide power to the home or office via a grounded neutral system. That is, of the two power delivery conductors, one is typically electrically connected to ground at one or more points within the system. This grounded power delivery conductor is known as “neutral”. The other, ungrounded conductor, is generally referred to as “hot”. 
   Many fault interrupters are configured as wall receptacle units. These receptacle interrupters generally have one or more local outlets built into the unit and into which an electrical appliance may be plugged. These receptacle fault interrupters often have two sets of electrical connection points called line and load. The line side electrical connection points are designated for connection to the power source. The load side electrical connection points are designated for connection to additional electrical branches which, in turn, may serve as the source for remote electrical outlets. When the fault interrupter is correctly installed, fault protection is provided to both the local outlet as well as to remote outlets. However, if the fault interrupter is installed backwards, that is, the designated load connections are attached to the power source and the designated line connections are attached to the remote outlets, then the fault interrupter may not be able to detect and/or interrupt certain classes of faults. 
   Even in a correctly wired fault interrupter, if the so-called neutral connection is broken or comes loose, then the fault interrupter may not provide fault protection. This is because most fault interrupters require the neutral connection in order to power the detection electronics and in order to source energy to fire the current interruption relay or circuit breaker. If the neutral connection is open (a so-called “open neutral” condition), then a fault may go undetected or, if detected, may not be interrupted. 
   The present application discloses a fault interrupter which uses a four pole, single throw switch to ensure that the fault interrupter is tolerant to a certain class of misinstallation known as line/load reversal. By adding open neutral detection and a means for detecting if hot and neutral connections are swapped, a high degree of robustness to misinstallation is provided. By adding a redundant circuit breaker mechanism that is engaged in the case of a malfunction in the fault detection electronics, a self-testing capacity may be provided. 
   Ground fault current interrupts that use a differential transformer to detect the current imbalance that is indicative of a fault condition have been in use since the 1960&#39;s. U.S. Pat. No. 3,736,468 (Reeves et al.) discloses a GFCI which uses a differential sense transformer, the secondary of which is amplified to trip a circuit breaker. 
   A circuit for detecting an open neutral condition and an open ground condition is described in U.S. Pat. No. 4,598,331 (Legatti). That invention relies upon a supplemental secondary winding on the differential transformer to detect an open neutral condition or an open ground condition. When either an open neutral or an open ground condition occurs, an electrical current through the supplemental secondary winding serves to trip a circuit breaker, thereby removing power. One problem with this approach is that if the GFCI is misinstalled with the source and load sides swapped, neither an open ground nor an open neutral condition is detectable. U.S. Pat. No. 6,040,967 (DiSalvo) describes a fault interrupter that prevents the engagement of a circuit breaker reset mechanism in the case of an open neutral condition. This is done by requiring power connections to both hot and neutral in order to latch the circuit breaker into a closed position. If the neutral connection is missing then it is not possible to reset a tripped circuit breaker. However, if the neutral connection is removed while the fault interrupter is in service, there will be no means to detect this condition or to trip the circuit breaker in the case of a fault. 
   Technologies that detect and indicate the occurrence of a miswiring condition include U.S. Pat. Nos. 3,800,961 (Kershaw) and 5,099,212 (Nagaishi) which disclose systems by which visual indicators can be used to indicate correct (or incorrect) connections to hot, neutral and ground. U.S. Pat. No. 6,560,079 (Hirsh et al.) discloses a system for detecting a loss of ground condition and transposed hot/neutral conductors in an electrical appliance. 
   The problem of line/load reversal occurs when a fault interrupter that is designed to provide both local power (through one or more faceplate outlets) as well as provide power and protection to downstream outlets, is wired incorrectly. This happens when the power source is connected to the terminals (the load terminals) that are designated to supply downstream electrical power and the down stream load is connected to the terminals (the line terminals) of the fault interrupter that are designated for connection to the power source. Line/load reversal is a problem because it can result in unprotected power to the uSerial 
   One solution which has been proposed for line/load reversal is the so-called lockout technology described in U.S. Pat. No. 6,245,558 (DiSalvo et al.). This technology requires power to enable a circuit breaker to be engaged after it has been tripped. If a fault interrupter having this technology is installed so that its line terminals are connected to the load side, once the circuit breaker is tripped, there will be no power available to reengage the circuit breaker. Another approach to the problem of line/load reversal is described in U.S. Pat. No. 6,522,510 (Finlay et al.) which uses a resistive element connected at one end to a hot power conductor and on the other end to either a breaker coil or to the gate or base of a switch element. When the fault interrupter is installed with line and load sides reversed, the circuit breaker is tripped, indicating to the installer that an error in installation has been made. The problem with the above two technologies is that while they both have indication means that the fault interrupter has been incorrectly installed, both can provide unprotected power at the local outlet (face power) until such time as the fault interrupter is installed correctly. 
   Fault interrupters can malfunction, causing the loss of protection against faults. Several solutions to the detection of defective fault interrupters have been proposed. U.S. Pat. Nos. 5,600,524 and 5,715,125 (Neiger, Gershen and Rosenbaum) describe an intelligent GFCI that automatically and periodically tests the fault detection electronics, indicating a malfunction via audible or visual means, and/or by tripping the circuit interruption means or both. The inventions do not test for the correct function of the fault interruption means. U.S. Pat. No. 6,262,871 (Nemir et al.) discloses a fail safe fault interrupter that automatically and periodically tests the fault sensing electronics and that tests for the operation of the fault interruption means and upon the detection of a malfunction, permanently trips a secondary circuit breaker, thereby removing the fault interrupter from service. 
   3. Objects and Advantages 
   The present invention encompasses a topology that enables a wall outlet fault interrupter to operate correctly and to provide safety if the line and the load terminals are misconnected, or, equivalently, removes the need to specify line terminals and load terminals. By incorporating open neutral and transversed conductor detection, the fault interrupter will automatically trip so that it never provides unprotected power either to faceplate or to downstream outlets as long as the fault detection/interruption electronics are operational. Finally, by incorporating a secondary system diagnosis and interruption means that is triggered by an auxiliary fault detection mechanism, the entire fault interrupt unit acquires a self-testing capacity. This allows it to fail safe even in the event of a failure of the fault detection electronics. To summarize, the present invention is an electrical fault protection device preferably designed for a wall receptacle implementation that provides the following features: 
   a) provides a fault detection function and fault interruption function; 
   b) can provide fault protection to downstream devices; 
   c) can be installed without regard to line and load sides of the installation; 
   d) provides ground assurance; 
   e) will detect an open neutral condition or swapped hot and neutral conductors; and 
   f) may be provided with a secondary circuit breaker actuation means that can provide redundant protection in the case of circuit malfunction. 
   SUMMARY OF THE INVENTION 
   This invention consists of a method and apparatus for fault detection that is robust to miswiring conditions and that provides redundant circuit breaker protection in the case of malfunction. By using a four pole single throw switch that is configured to interrupt both power flow into a faceplate (local) outlet(s) as well as power supplied to a remote outlet(s), power interruption is assured to all service points in the case of a fault. Furthermore, by using redundant current sense coils, ground fault detection can be accomplished irrespective of the wiring orientation with the four pole switch providing protection irrespective of line/load orientation. Finally, by incorporating an auxiliary self-testing means, robustness to circuit defect or malfunction is accomplished. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG.  1 —Block diagram of standard ground fault interrupt circuit 
     FIG.  2 —Block diagram of a fault interrupter with line and load terminals reversed 
     FIG.  3 —Block diagram of the approach of the present invention 
     FIG.  4 —Block diagram of the approach using two three pole switches 
     FIG.  5 —Specific embodiment using a four pole single throw switch 
     FIG.  6 —Specific embodiment incorporating open neutral and transposed conductor detection 
     FIG.  7 —Specific embodiment incorporating ground assurance, transposed conductor detection and the ability to detect a low impedance loadside connection between ground and neutral. 
   

   LIST OF REFERENCE NUMERALS 
   
       
         2 —power source 
         3 —Hot conductor 
         4 —Input terminal 
         5 —Neutral conductor 
         6 —Input terminal 
         8 —Output terminal 
         10 —Output terminal 
         11 —Detection/interruption module 
         12 —Fault interrupt receptacle 
         14 —Load 
         16 —Plug 
         20 —Hot side power cord 
         22 —Source conductor 
         24 —Source conductor 
         26 —Current sense coil (transformer) 
         28 —Secondary from current sense transformer 
         30 —Detection electronics 
         32 —Hot side primary circuit breaker switch 
         33 —Neutral side primary circuit breaker switch 
         34 —Appliance load 
         36 —Solenoid 
         37 —Ground fault from appliance load 
         38 —Ground fault from conductor 
         39 —Ground 
         40 —Ground fault 
         41 —Ground fault from conductor 
         42 —Thyristor 
         43 —Ground fault from appliance power cord 
         44 —Conductor delivering power to detection electronics 
         46 —Conductor delivering power to detection electronics 
         50 —Test button 
         52 —Test fault resistance 
         54 —Load side outlet 
         56 —Local outlet 
         58 —Conductor on load side 
         60 —Conductor on load side 
         62 —Current sense transformer 
         64 —Current sense transformer 
         66 —Side A switch 
         68 —Side B switch 
         70 —Four pole single throw switch/circuit breaker 
         72 —Side A terminal  1   
         74 —Side A terminal  2   
         76 —Side B terminal  1   
         78 —Side B terminal  2   
         80 —Ground slot 
         82 —Ground terminal 
         84 —Conductor on ungrounded (hot) 
         86 —Conductor on ungrounded (hot) 
         88 —Conductor on ungrounded (hot) power delivery to local outlet and electronics 
         90 —Conductor on grounded (neutral) 
         92 —Conductor on grounded (neutral) 
         94 —Conductor on grounded (neutral) power delivery to local outlet and electronics 
         96 —Secondary of current sense transformer 
         98 —Secondary of current sense transformer 
         100 —Nodes connecting the two secondaries into the detection electronics 
         102 —Resistor 
         104 —Thyristor 
         106 —Resistor 
         108 —Node connecting to solenoid 
         110 —Gate of thyristor  104   
         112 —Shorting bar 
         114 —Shorting bar 
         116 —Electrical contact point (node) 
         118 —Electrical contact point (node) 
         120 —Electrical contact point (node) 
         122 —Diode 
         124 —Diode 
         126 —Diode 
         128 —Diode 
         130 —Resistor 
         132 —Break in neutral conductor 
         134 —Thyristor gate 
         138 —Self test module 
         140 —Resistor 
         142 —Resistor 
         144 —Resistor 
         146 —Test button signal pick off point 
         148 —Fault detect signal 
         150 —Auxiliary circuit interruption means 
         151 —load 
         152 —Current induction coil for loadside neutral to ground fault 
         154 —Auxiliary thyristor 
         158 —Resistor 
         164 —Resistor 
         166 —Secondary of neutral to ground sense coil 
         168 —Zener diode 
         170 —Node at junction of voltage divider 
     
  
   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1  gives a block diagram that functionally describes the majority of present day ground fault current interrupt (GFCI) devices. This is the prior art circuit that is the basis for almost any such device found in the home or in commercial or industrial facilities. An arc fault circuit interrupt has a similar construction but with a more complicated fault sensing component. Although the present description will be directed at ground fault current interrupters, the exposition may be extended to other classes of fault interrupters. The fault interrupt receptacle  12  consists of a detection/interruption module  11  together with a current sense coil  26  for fault sensing and a local electrical outlet  56 . Although in  FIG. 1 , a single local outlet  56  is depicted, local outlet  56  can represent multiple outlets, all of which are electrically parallel connected. The fault interrupt receptacle  12  is designed for attachment on one side to an alternating current power source  2  by connecting the source  2  to the input terminals  4  and  6  of the ground fault interrupt receptacle  12 . The ground fault interrupt receptacle  12  is designed for attachment to a load  14  by using output terminals  8  and  10 . Power is delivered from the source  2  via conductors  3  and  5 . In the U.S., one of these conductors (for this discussion, conductor  5 ) is generally required by electrical code to be grounded at the distribution panel and is known as the “neutral” conductor. In such a system, the ungrounded current carrying conductor is often called the “hot” conductor. Within the fault interrupt receptacle  12  and attaching to input terminals  4  and  6  are conductors  22  and  24 . Conductors  22  and  24  pass through a current sense transformer  26 , thereby acting as the primary for that transformer  26 . The secondary  28  of the current sense transformer  26  connects to the detection electronics  30 , which may filter and/or amplify and/or otherwise process the voltage from the secondary windings  28  of the current sense transformer  26 . 
   The detection electronics  30  derive power from conductors  44  and  46 . In normal operation, electrical current is delivered to the load  14  through circuit breaker switches  32  and  33 . In some applications, such as in a load distribution panel, there is a single circuit breaker switch  32  for interrupting electrical current on the ungrounded conductor and there is no circuit breaker switch  33  (equivalently, circuit breaker switch  33  is always closed). For a system with two circuit breaker switches  32  and  33 , circuit breaker switches  32  and  33  are closed during normal operation but are driven to be in an open position by solenoid  36  if a fault condition is sensed. Collectively, switches  32  and  33  are known as a double pole, single throw switch, since there are two independent switches (double pole), they conduct electricity in only one position (single throw), and they operate in lock-step, that is, they are configured to always have the same state, either open or closed. 
   In  FIG. 1 , the load  14  comprises a set of conductors attached to the load side terminals  8  and  10 , plus one or more outlets, represented by a single load side outlet  54 , plus any electrical appliance loads  34  that are attached to the load side outlet  54  via a plug-in connection. An example appliance load  34  is depicted in  FIG. 1  and is attached using a plug  16  on a power cord  20 . 
   In  FIG. 1 , ground faults  37 ,  38 ,  41 , and  43  are depicted with dashed lines to indicate that these are not always present. These represent fault events that a GFCI is designed to sense and to remedy by opening the circuit breaker switches  32  and  33 . Any of ground faults  37 ,  38 ,  41  or  43  could represent a human being that has come into electrical contact with a high potential conductor and with ground  39  with an attendant possibility of electrical injury. 
   In normal operation, in the absence of a ground fault, the same amount of electrical current flows in conductors  22  and  24  but in opposite directions. The net magnetic flux in the differential current sense transformer  26  is then zero and the voltage that is generated in the transformer secondary  28  is zero. When circuit breaker switches  32 ,  33  are closed and a ground fault  37 ,  38 ,  41  or  43  occurs, then there is a current imbalance between conductors  22  and  24 . This results in a nonzero net magnetic flux being induced in the differential current sense transformer  26 . This results in a nonzero voltage being induced in the secondary  28  of the transformer  26 . The detection electronics  30  then takes this voltage and processes it to determine if a fault of sufficient magnitude and/or duration is taking place. If the detection electronics  30  determines that an objectionable fault is occurring, then it triggers a thyristor  42 , which energizes a solenoid  36  which opens the circuit breaker switches  32  and  33 . This serves to remove power from the load side and, therefore, to any fault. 
   In ground fault interrupt devices that are designed for an electrical system that uses a grounded neutral, there is generally a second current induction coil that is designed to detect low impedance connections between the neutral and ground at the load side of the GFCI device (fault  41 ). Without this induction coil, a neutral to ground fault  41  may be hard to detect since it involves very low currents. For the sake of clarity, this second coil is not depicted in  FIG. 1 . 
   Test button  50  allows a manual test of the proper operation of the fault sensing/interrupting circuitry. When test button  50  is manually engaged, it causes a current flow through test resistor  52 , resulting in an electrical leakage around the differential current sense transformer  26 . This imbalance results in a voltage across the secondary  28  and is recognized as a fault by the detection electronics  30 . The detection electronics  30  then energize thyristor  42 , causing the circuit breaker contacts  32 ,  33  to be opened. A user can thus manually test the GFCI by engaging the test button  50  and then listening for the relay contacts  32 ,  33  to open or by observing a visual indication that the circuit breaker contacts  32 ,  33  have opened. 
   Although  FIG. 1  is a representative embodiment of a GFCI, there are many possible permutations. For example, the detection electronics  30  in  FIG. 1  may be simply a pass through connection to the gate of thyristor  42 , in which case the secondary  28  of differential transformer  26  generates sufficient energy to trigger thyristor  42 . Alternatively, the detection electronics  30  may consist of transistors, operational amplifiers and other components to amplify and/or filter the voltage developed on secondary  28 . The solenoid  36  and/or the test button  50  may receive power from the load side of circuit breaker contact  32  as shown, or may be connected on the source side of circuit breaker contact  32 . The solenoid  36  may be energized by a thyristor  42  as depicted, or may be energized by a transistor or other type of switch. The solenoid  36  may be replaced by an alternative type of trip mechanism such as a bimetallic element or a fusible link. 
   In  FIG. 1 , the ground fault interrupt receptacle  12  consists of the detection/interruption module  11  together with a current sense coil  26  and a local outlet  56 . Physically, this outlet  56  (and possibly additional parallel connected outlets) is contained within the GFCI receptacle  12 . Electrically, this outlet  56  is parallel connected with load outlet  54  and so a ground fault that occurs in an appliance that is plugged into outlet  56  will be recognized by the detection electronics  30  and then interrupted by circuit breaker switches  32  and  33  in an identical way as for load outlet  54 . 
     FIG. 1  represents a somewhat general topology inasmuch as there can be local outlet(s)  56  and remote load outlet(s)  54 . In some embodiments, the ground fault interrupt receptacle  12  will not be designed for connection to remote outlets and output terminals  8  and  10  will be missing. Only outlet  56  will be present. In other embodiments, the ground fault receptacle will not contain any local outlets. In such a case, the face of the ground fault receptacle might have a test and reset button but no outlets. Such embodiments are specifically designed to protect downstream outlets (that is, one or more load outlets like load outlet  54 ). Most GFCI outlets sold in the U.S. today have one or more local outlets  56  and also have output load terminals  8  and  10  to allow the connection of multiple downstream load outlets  54  and thus to provide maximum flexibility. This could be useful, for example, in a bathroom where one outlet is a GFCI outlet, and a second outlet is a standard outlet that is wired to, and receives power from, the load side of the first outlet and that consequently receives GFCI protection from the first outlet. 
   A possible wiring fault can occur if either of the input terminals  4  or  6  is loose or not connected. Assuming a grounded neutral electrical system where conductor  24  is on the neutral side, we can see that if the connection to the neutral side terminal  4  alone is unconnected, power can still be supplied to a ground fault (since the hot side terminal  6  is connected) but it will not be possible to detect or to interrupt a fault at the local outlet  56  or the remote load outlet  54 . This is because the detection electronics rely upon both connections  44  and  46  to, respectively, the hot and neutral conductors in order to receive power. If the neutral side conductor is not connected, then it is not possible to deliver power to the detection electronics  30  via line  46 . Furthermore, the solenoid  42  requires the connection of line  24  in order to be fired into conduction and to thereby trip the circuit breaker switches  24  and  33 . So, the loss of a neutral connection (a so-called “open neutral” condition) compromises both fault detection and fault interruption. 
     FIG. 2  illustrates the situation where a ground fault interrupt device is miswired with the output terminals  8  and  10  connected to the source  2  and the input terminals  4  and  6  are connected to the load  14 . This is known as a swapped line/load condition. The load side outlet  54  is still protected since any ground fault causes an imbalance in the current flowing in conductors  24  and  22 , in turn causing a voltage in the transformer secondary  28  which is detected by the detection electronics  30  and causes an opening of the circuit breaker switches  24  and  33 , thereby removing power from the fault. Also, the test button  50  still functions, causing a simulated fault to occur and causing the circuit breaker switches to open. From the manual test using test button  50 , the user would expect that the ground fault interruption protection is working. However, ground faults that occur in any appliance plugged into local outlet  56  will not be detected. This is because any ground fault that occurs at the electrical location of outlet  56  does not result in a current imbalance in the sense transformer  26 . Accordingly, there is no imbalance in transformer  26  and hence no trip of the circuit breaker switches  24  and  33 . Furthermore, even if there were a trip of circuit breaker switches  24  and  33 , it would not protect local outlet  56  or appliances plugged into local outlet  56 . This is because the circuit breaker switches are not located between local outlet  56  and the source  2  and so they are unable to interrupt power delivery to outlet  56 . The problem of swapped line/load terminals is a common problem in electrical installations. It can occur because of receptacle installation by nonprofessionals. However, even trained electricians can make installation mistakes. It is for this reason that the receptacle design of the present invention, that is indifferent to the connection order of line and load, is desirable. 
     FIG. 3  depicts a block diagram of the present invention. The key idea is to provide the ability to sense a fault and to interrupt the circuit on both sides of the fault detection electronics/local outlet so that the orientation of the receptacle at the time of installation is immaterial to the derived safety. In  FIG. 3 , the two sides of the receptacle  12  are denoted as SIDE A and SIDE B. There are two current sense transformers  62  and  64  to detect a current imbalance. If SIDE A is attached to the source and SIDE B is attached to one or more loads or remote outlets, then if a ground fault occurs in an appliance that is plugged into local outlet  56 , it will cause a current imbalance in the conductors running through sense transformer  62  and will be detected as a fault by the detection electronics (note that the secondaries of transformers  62  and  64  will be connected to the detection/interruption module  11  but these connections are not shown in  FIG. 3 ). In a similar way, if a ground fault occurs in the loads, outlets or appliances attached to SIDE B, they will cause a current imbalance in the conductors running through transformer  64  as well as transformer  62  and so this ground fault condition is detectable. Whenever a fault is detected, both sets of switches  66  and  68  are controlled to open to remove power from the fault. This ensures that power delivery to the fault is always interrupted subsequent to a fault occurrence. 
   If the receptacle  12  is installed so that SIDE B is attached to the source and SIDE A is attached to the load, then transformer  64  provides fault detection for ground faults in appliances attached to local outlet  56  and both transformers  64  and  62  will detect a ground fault that occurs on the load side. Regardless of the source of the fault, upon the detection of a fault, both sets of switches  66  and  68  are opened, guaranteeing that power is removed from a ground fault. Accordingly, in terms of the ability to detect and interrupt a fault, this topology is insensitive to the particular orientation of the receptacle  12  that happens to be implemented at the time of installation. It also provides a degree of redundant protection to remote outlets if one of the sense coils fails. 
     FIG. 4  depicts an alternative switch configuration for a fault interrupt receptacle  12 . As in  FIG. 3 , current sense transformers  62  and  64  serve to detect a current imbalance that is indicative of a fault condition. The secondaries of both transformers  62  and  64  are connected to the detection/interruption module  11  (connections not shown). Shorting bars  112  and  114  are used to connect Side A, Side B and the local outlet  56  and detection/interruption electronics  11  to applied power. The topology is completely symmetrical, so, the source can be attached to Side A and the load to Side B, or vice versa, with either orientation resulting in protected power delivery to the local outlet  56  and to remote outlets or loads that are attached to the side opposite to the source side. The function of shorting bar  112  is to engage to make electrical contact with nodes  116 ,  118  and  120  when resetting the receptacle  12  and to mechanically separate from nodes  116 ,  118  and  120  when interrupting power. Shorting bar  114  operates in an identical way as shorting bar  112  and operates in tandem with shorting bar  114 , that is, when shorting bar  112  is engaged, so is shorting bar  114 . When shorting bar  112  is released, so is shorting bar  114 . One advantage to configuring the switch into a shorting bar type of topology is that the shorting bar  112  may be mechanically configured to have a triangular arrangement with contacts on the three corners and force application occurring at the center. This will result in even forces being distributed over the three contacts. 
     FIG. 5  depicts a block diagram for the preferred embodiment of circuit breaker switches of the present invention as they might be used in a ground fault interrupt receptacle. Conductors  88  and  94  provide power to the local outlet  56  and act as primary windings for transformer  62 . Conductors  86  and  92  provide power to/from side B and act as primary windings for transformer  64 . The secondary  96  of transformer  62  and the secondary  98  of transformer  64  feed together into the detection electronics  30 . In  FIG. 5 , this is depicted as a parallel connection of the secondaries  96  and  98  through nodes  100 . However, the connection of these secondaries may be made in a way other than a direct connection. When the detection electronics  30  detects a fault condition and fires the thyristor  42 , it serves to energize the solenoid  36 , thereby causing the four pole single throw switch  70  to open, with all four switches opening at the same time. In the absence of a fault, a reset mechanism (not shown) may be used to engage the switch  70  into a closed position, thereby powering the local outlet  56  and the detection electronics  30 . As per the discussion regarding  FIG. 3 , the system in  FIG. 5  is symmetrical and may be connected to source or to load on either side while still providing a ground fault detection/interruption capability at the local outlet  56  as well as any connected loads. If Side A is connected to the power source, then a ground fault that occurs on Side B causes an imbalance in current flow between conductors  86  and  92  and is sensed using transformer  64 . If side B is connected to the power source, then a ground fault that occurs on Side B causes an imbalance in current flow between conductors  86  and  92  and is sensed using transformer  64 . Regardless of which side is connected to the power supply, anytime that a ground fault occurs in the power cord or within an appliance that is plugged into outlet  56 , it will cause a current imbalance between conductors  88  and  94  and will be sensed by transformer  62 . 
     FIG. 5  illustrates the connection of a ground. Ground terminal  82  is generally provided on the receptacle  12  as a screw terminal. This connection is then designed to be electrically connected to earth ground  39 . In many installations, a ground fault receptacle  12  will be mounted into a grounded outlet box with the screw connections between receptacle  12  and the outlet box serving to establish the ground connection. The local outlet  56  will have a third slot (generally half round in the U.S. system) that is designated for ground connection. 
   Assume that in  FIG. 5 , terminal  72 , conductor  84 , conductor  88 , conductor  86  and terminal  76  are designated as the “hot” or ungrounded power delivery elements. Then terminal  74 , conductor  90 , conductor  94 , conductor  92  and terminal  78  are designated as the “neutral” or grounded power delivery elements. Given these definitions, by the addition of resistors  102  and  106  and thyristor  104 , open neutral and line transversal protection can be provided. In  FIG. 5 , node  108  is attached to one side of solenoid  36  and is attached to the anodes of thyristors  42  and  104  (note that node  108  appears in two places in  FIG. 5 ). The neutral conductor is attached to ground at one or more remotely located points in the electrical distribution system, usually at a load distribution panel. Because of this connection, the neutral conductor  94  will have a potential very close to ground potential and the voltage at the gate  110  of thyristor  104  will be close to ground potential and so thyristor  104  will be inhibited from firing. If an open neutral condition occurs, then the gate  110  of thyristor  104  attains a voltage that is derived from a voltage divider made up of resistors  102  and  106  and taken from the hot conductor  88  to ground  39 . The thyristor  104  is fired, causing a momentary current flow into ground  39  and thereby firing solenoid  36 , even in the absence of a neutral connection. This serves to open the circuit breaker contacts  70 . 
     FIG. 6  depicts a circuit that will force the circuit breaker switches to open in the case of an open neutral condition or in the case of swapped hot and neutral connections at the source terminals. In  FIG. 6 , a source  2  is assumed to be connected to the terminals  72  and  74  and a load  151  is assumed to be connected to terminals  76  and  78 . This is for the purposes of explanation, although, as is readily seen, the circuit is completely symmetric between terminal pair  72 ,  74  and terminal pair  76 ,  78  and so the choice of which side to connect to source  2  and to load  151  is arbitrary. As discussed previously, load  151  can represent one or more remote outlets, a light, a motor or any one of numerous possible AC electrical appliances that might be connected on the load side of fault receptacle  12 . It is further assumed that the fault interrupt receptacle  12  is connected to ground  39  through the designated ground terminal  82  that is present on most fault interrupt receptacles. Diodes  122 ,  124  and  126  serve a dual function. First, they ensure isolation between the neutral conductor  94  and the ground terminal  82 . Diode  126  prevents current flow from ground  39  to neutral on a path through diode  122 , and thyristor  42  blocks current flow from going in the other direction to the ground terminal  82 . Similarly, diode  122  prevents current flow from the neutral conductor  94  to the ground terminal  82  through the path that goes through diodes  124  and  126 , and thyrister  42  blocks the reverse current flow, preventing it from flowing through the path through diode  122 . 
   The detection electronics  30  are connected between the hot conductor  88  and the neutral conductor  94 . When a fault is detected, the detection electronics  30  identifies the event and then responds by firing the gate  134  of the thyristor  42 . This has the effect of causing current to flow from the hot conductor  88  through solenoid  36 , and through thyristor  42 , thereby causing the circuit breaker switches  70  to open. When the neutral connection from the power source is secure and is attached to ground at a remote location, the voltage potential difference of the neutral line  94  should be very close to a ground potential. All diodes have a forward voltage drop. For silicon diodes, this drop is generally between 0.6 and 0.7 volts. So, diode  122  represents a voltage stand-off from ground of about 0.65 volts and diodes  124  and  126  represent a voltage stand-off from ground of about 1.3 volts. Accordingly, if the neutral line  94  is holding a ground potential, when thyristor  42  is fired, all solenoid current should flow through diode  22  to the neutral line  94  and none should flow through diodes  124  and  126  into ground  39 . 
   If a break or bad connection (depicted as a discontinuity  132 ) causes the neutral conductor  90  to become disconnected, this results in the so-called “open neutral condition”. Alternatively, if the lowermost switch of the four pole single throw switch  70  is open, this will result in an open neutral condition. With an open neutral condition, the detection electronics block  30  is nonfunctional because it needs connections to two distinct voltage potentials in order to have internal power for running detection electronics, thereby rendering the detection electronics unable to detect a fault condition. However, since the detection electronics does not have a connection to neutral, the entire detection electronics circuit, including the thyristor gate  134  floats to attain the potential of the hot conductor  88 . Since the cathode  136  of thyristor  42  has a potential that is only two diode drops away from ground, thyristor  42  is fired with the current going through diodes  124  and  126  into ground  39 . Thus, an open neutral condition results in the opening of circuit breaker switches  70 . 
   During normal operation, diode  128  will never have a forward bias and so it will not conduct electrical current. Similarly, during an open neutral condition, diode  128  will not have a forward bias. However, if a connection is made so that the neutral and the hot conductors are miswired, that is, the hot conductor  84  is attached to the source neutral conductor and the neutral conductor  90  is attached to the source hot, then current will flow in diode  128  and resistor  130 , causing the firing of thyristor  42  into diodes  124  and  126  and thereby into ground  39 , resulting in the opening of the circuit breaker switches  70 . This provides protection against the occurrence of transposed source connections where the hot side of the source is connected to 
   As discussed in conjunction with  FIG. 5 , the current sense transformers  62  and  64  are used to sense current imbalances on the line and load sides of the fault interrupt receptacle. In  FIG. 6 , the secondaries  96  and  98  are electronically monitored by the detection electronics  30  but the connections are not shown. 
   The self-test block  138  in  FIG. 6  serves to provide a redundant means to check the correct performance of the overall circuit function. This acts as a means for the so-called “end-of-life” feature whereby the fault interrupter receptacle either signals an inoperable status or permanently removes power from the local outlet  56  and remote load  152 . The self test block  138  is simply an electronic delay circuit. Any time that either a manual test occurs or a fault event is sensed, the self test block  138  delays for a period of time (say 50 milliseconds) which is an amount that should be more than sufficient to open the circuit breaker switches  70 . After that amount of time, the self test block then fires a control line  150  using power derived from lines  88  and  94 . In the absence of a malfunction in the detection/interruption electronics, this control action will be meaningless. This is because the circuit breaker contacts  70  will have already been opened and so there is no power available to trip an interrupter. Control line  150  could be used as an additional gate trigger for thyristor  42  and/or it could be used to open a redundant circuit interruption means (not shown). If the fault detection/interruption means functioned correctly, then the circuit breaker switches  70  should have opened, and control line  150  has no power. However, if the circuit breaker switches  70  have not opened, this suggests the presence of a malfunction within the fault interrupt receptacle and this malfunction may be in the sensing electronics  30  or in the fault interruption portion which consists of thyristor  42  and solenoid  36  and circuit switches  70 . So, the output  150  from the self test block  138  can be used to blow a fuse (not shown) and thereby providing a visual or audible indicator to be permanently turned on, and/or it can be used to activate an auxiliary circuit interruption means that is independent of solenoid  36  and thyrister  42 . 
   To recap, the self test block  138  is activated any time that a fault is sensed by the detection electronics  30 . In addition, the self test block is activated any time that the manual test button  50  is engaged. So this approach to self diagnostics is automatic (since it automatically occurs any time a fault is sensed) and it is also manual since it can be implemented through activation of the manual test button  50 . 
   Although not discussed in conjunction with  FIGS. 1 through 6 , almost all commercial GFCI&#39;s have a provision for detecting a low impedance connection to ground on the load side of the GFCI. That is, they are equipped to detect a load side connection between the neutral conductor and ground. This is important because if there is a load side ground connection, then it is possible that a person could come in contact with hot and ground with the ground current then returning on the neutral line. The result would be a ground fault but with no current imbalance in the current sense transformer, resulting in an unrecognized ground fault. The solution is to use an auxiliary current induction coil or transformer which detects the presence of a low impedance path to ground from the neutral conductor. 
     FIG. 7  portrays the interchangeable line/load circuit of the present invention with the addition of a current induction coil  152  for sensing a low impedance path from neutral to ground on the load side of the fault interrupt receptacle  12 . Both power delivery conductors that transfer power from Side A to Side B go through this current induction coil  152  one time. If there is a low impedance path to ground on the load side of this coil, it will cause loop currents that will be sensed via secondary  166  by the detection electronics  30  (the connection between secondary  166  and detection electronics  30  is not shown). If the fault is of sufficient magnitude and/or duration, the detection electronics  30  then fires the thyristor  42  and thereby causes circuit breaker  70  to open. The power delivery conductors that furnish power to outlet  56  go through the sense coil  152  twice. The reason that different numbers of turns are used for the conductors that pass power from Side A to Side B as opposed to the conductors that pass power to the local outlet  56  is to avoid cancellation effects that might occur if the turns were the same, power came from Side A to local outlet  56  and a low impedance load side neutral to ground connection was present. There are other combinations of primary winding numbers and sense that will ensure that there is never a cancellation of neutral to ground effects. 
     FIG. 7  also portrays an alternative for ensuring that the receptacle  12  is grounded and for ensuring that the hot and neutral connections are made correctly. This is done by using an auxiliary thyristor  154 . During normal operation, thyristor  42  is the active device upon the detection of a fault by the detection electronics  30 . Auxiliary thyristor  154  can serve the same role as thyristor  42 . That is, when it is fired it serves to activate solenoid  36 , which in turn, causes switch  70  to open. Resistors  158  and  164  form a voltage divider between the hot side conductor  88  and ground  39 . In its preferred embodiment, resistor  158  will be a relatively large value to limit the current introduced into ground  39  and resistor  164  will be a relatively small value so that in normal operation, the voltage at node  170  will be relatively small. If the ground connection  82  is missing, then the voltage at node  170  will be periodically pulled positively to the potential of hot conductor  88 . When the node  170  voltage exceeds the reverse breakdown voltage on zener diode  168 , it will cause the firing of thyristor  154 . In this way, the circuit provides ground assurance so that if the ground connection is missing, the circuit breaker contacts  70  are opened. Even when the ground connection is secure, it is possible that the ground  39  and the neutral  94  connections can have potentials that are several volts different. This can happen due to voltage drops in the neutral line that are due to current flow through conductor resistances. Zener diode  168  serves to provide a margin of voltage stand-off between ground and neutral potentials. An open ground condition is only sensed if node  170  exceeds the voltage at the gate of thyristor  154  by an amount greater than the zener voltage value. This allows the avoidance of false tripping. 
   In a grounded neutral system, if conductors  84  and  90  are transposed, that is, conductor  90  is connected to the hot side of the source and conductor  84  is connected to the neutral side of the source, then the voltage at the cathode of thyristor  154  will be periodically much more negative than the voltage at node  170 . When the voltage difference significantly exceeds the voltage on zener diode  168 , it will cause a firing of thyristor  154 . In this way, the circuit depicted in  FIG. 7  provides protection against miswiring of the hot and neutral power because any time that miswiring occurs, the circuit breaker will trip upon energization by the source. 
   Although the invention has been described in detail with particular reference to these preferred embodiments, other embodiments can achieve the same results. Variations and modifications of the present invention will be obvious to those skilled in the art and it is intended to cover in the appended claims all such modifications and equivalents. The entire disclosure of all references, applications, patents and publications cited above are hereby incorporated by reference.