Abstract:
The present invention is directed to a device that includes a housing assembly including a plurality of line terminals, a plurality of load terminals, and a plurality of receptacle load terminals coupled to the plurality of load terminals by a plurality of conductors. A circuit interrupting assembly is disposed in the housing and coupled to the plurality of line terminals or the plurality of load terminals, the circuit interrupting assembly establishing electrically continuity between the plurality of line terminals and the plurality of load terminals in a reset state and interrupting the electrical continuity between the plurality of line terminals and the plurality of load terminals in a tripped state. A wiring state detection circuit is coupled to the plurality of line terminals or the plurality of load terminals. At least one switchable element is coupled to the wiring state detection circuit, the at least one switchable element including a plurality of switching states. The at least one switchable element is disposed in at least one of the plurality of conductors coupled between the plurality of receptacle load terminals and the plurality of load terminals. The at least one switchable element is also configured to change switching states in response to a stimulus generated by the wiring state detection circuit.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   This is a continuation of U.S. patent application Ser. No. 11/063,067, filed on Feb. 22, 2005, now U.S. Pat. No. 7,295,410 U.S. patent application Ser. No. 11/063,067 is a continuation-in-part of U.S. patent application Ser. No. 10/964,217, filed on Oct. 13, 2004, now U.S. Pat. No. 7,239,491 the contents of which is relied upon and incorporated herein by reference in their entirety, and the benefit of priority under 35 U.S.C. §120 is hereby claimed. 

   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates generally to wiring devices, and particularly to protective wiring devices. 
   2. Technical Background 
   Electrical distribution systems that provide power to a house, building or some other facility include one or more breaker panels coupled to a source of AC power. The breaker panel provides AC power to one or more branch electric circuits installed in the structure. The electric circuits may typically include one or more receptacle outlets and may further transmit AC power to one or more electrically powered devices, commonly referred to in the art as load circuits. The receptacle outlets provide power to user-accessible loads that include a power cord and plug. Because certain types of faults have been known to occur in electrical wiring systems, each electric circuit typically employs one or more electric circuit protection devices. The most common protective device is a ground fault circuit interrupter (GFCI). 
   Both receptacle wiring devices and electric circuit protective wiring devices are disposed in an electrically non-conductive housing. The housing includes electrical terminals that are electrically insulated from each other. Line terminals couple the wiring device to wiring that provides AC electrical power from the breaker panel. Load terminals are coupled to wiring that directs AC power to one or more electrical loads. Load terminals may also be referred to as “feed through” terminals because the wires connected to these terminals may be coupled to a daisy-chained configuration of receptacles or switches. The load may ultimately be connected at the far end of this arrangement. As alluded to above, power may be accessed by “user accessible” load terminals, commonly referred to as “receptacle terminals.” The receptacle terminals are in communication with receptacle openings disposed on the face of the housing. This arrangement allows a user to insert an appliance plug into the receptacle openings to thereby energize the device. 
   As noted above, there are several types of electric circuit protection devices. For example, such devices include ground fault circuit interrupters (GFCIs), ground-fault equipment protectors (GFEPs), and arc fault circuit interrupters (AFCIs). This list includes representative examples and is not meant to be exhaustive. Some devices include both GFCIs and AFCIs. As their names suggest, arc fault circuit interrupters (AFCIs), ground-fault equipment protectors (GFEPs) and ground fault circuit interrupters (GFCIs) perform different protective functions. 
   An arc fault typically manifests itself as a high frequency current signal. Accordingly, an AFCI may be configured to detect various high frequency signals and de-energize the electrical circuit in response thereto. 
   A ground fault occurs when a current carrying (hot) conductor creates an unintended current path to ground. A differential current is created between the hot/neutral conductors because some of the current flowing in the circuit is diverted into the unintended current path. The unintended current path represents an electrical shock hazard. Ground faults, as well as arc faults, may also result in fire. 
   A “grounded neutral” is another type of ground fault. This type of fault may occur when the load neutral terminal, or a conductor connected to the load neutral terminal, becomes grounded. While this condition does not represent an immediate shock hazard, it may lead to serious hazard. As noted above, a GFCI will trip under normal conditions when the differential current is greater than or equal to approximately 6 mA. However, when the load neutral conductor is grounded the GFCI becomes de-sensitized because some of the return path current is diverted to ground. When this happens, it may take up to 30 mA of differential current before the GFCI trips. Therefore, if a double-fault condition occurs, i.e., if the user comes into contact with a hot conductor (the first fault) when simultaneously contacting a neutral conductor that has been grounded on the load side (the second fault), the user may experience serious injury or death. 
   One problem that is associated with protective devices relates to the protective device being miswired, or reverse wired, in the field by an installer. Miswiring refers to a situation wherein an installer connects the line terminals to the load side of the electric circuit and connects the load terminals to the AC power source. Miswiring may result in the protective device not protecting the user from the fault conditions described above. Labels and installation instruction sheets have been used to prevent miswiring. However, instructive material may be ignored by an installer. 
   Another problem is that protective devices, like all electrical devices, have a limited life expectancy. When the device has reached end of life, certain components may fail, such that the user may not be protected from the fault condition. End of life failure modes include failure of device circuitry, failure of the relay solenoid, and/or failure of the solenoid driving device, typically a silicon controlled rectifier (SCR). Test buttons have been incorporated into protective devices to provide the user with a means for testing the effectiveness of the device. One drawback to this approach lies in the fact that if the user fails to use the test button, the user will not know if the device is functional. Even if the test is performed, the test results may be ignored by the user for various reasons. 
   What is needed is a protective device configured to reliably protect the user from a fault condition in the electrical power distribution system. A protective device is needed that is configured to detect, and indicate, that a miswire condition is extant. A protective device is further needed that denies power to the portion of the electrical power distribution system experiencing the fault condition. Further, a protective device is needed that is equipped to decouple the load terminals from the line terminals in the event of an end of life condition. 
   SUMMARY OF THE INVENTION 
   The present invention addresses the needs described above by providing a protective device configured to reliably protect the user from a fault condition in the electrical power distribution system. The protective device of the present invention is configured to detect, and indicate, that a miswire condition is extant. The present invention denies power to the portion of the electrical power distribution system experiencing the fault condition. Further, the present invention is equipped to decouple the load terminals from the line terminals in the event of an end of life condition. 
   One aspect of the present invention is directed to an electrical wiring protection device that includes a housing assembly including a plurality of line terminals, a plurality of load terminals, and a plurality of receptacle load terminals. A fault detection circuit is coupled to at least one of the plurality of line terminals. The fault detection circuit is configured to generate a fault detection signal in response to detecting at least one fault condition. A first interrupting contact assembly is coupled to the fault detection circuit. The first interrupting contact assembly includes first interrupting contacts disposed between the plurality of line terminals and the plurality of load terminals. The first interrupting contacts are configured to electrically couple the plurality of line terminals and the plurality of load terminals in a reset condition. The first interrupting contacts are configured to decouple the plurality of line terminals from the plurality of load terminals in response to the fault detection signal in a tripped state. A wiring state detection circuit is coupled to at least one of the plurality of line terminals. The miswire detection circuit is configured to generate a first wiring signal when the plurality of line terminals are connected to a source of AC power. A second interrupting contact assembly is coupled to the wiring state detection circuit. The second interrupting contact assembly includes second interrupting contacts disposed between at least one of the plurality of receptacle load terminals and at least one of the plurality of feed-through load terminals. The second interrupting contacts are configured to electrically couple the at least one receptacle load terminal to the at least one feed-through load terminal in response to the first wiring signal. 
   In another aspect, the present invention includes a method for protecting a user from a fault condition in an electrical circuit. The method includes providing an electrical wiring protection device that includes a housing assembly having a plurality of line terminals, a plurality of load terminals, and a plurality of receptacle load terminals. The electrical wiring protection device also includes first interrupting contacts disposed between the plurality of line terminals and the plurality of load terminals. Second interrupting contacts are disposed between at least one of the plurality of receptacle load terminals and at least one of the plurality of feed-through load terminals. The second interrupting contacts are initially disposed in an open state. A wiring status signal is provided that is configured to indicate whether the plurality of line terminals are coupled to the source of AC power. The second interrupting contacts are closed in response to the wiring status signal indicating that the plurality of line terminals are coupled to the source of AC power. 
   In another aspect, the present invention includes a method for protecting a user from a fault condition in an electrical circuit. The method includes providing an electrical wiring protection device that includes a housing assembly having a plurality of line terminals, a plurality of load terminals, and a plurality of receptacle load terminals. The electrical wiring protection device also includes first interrupting contacts disposed between the plurality of line terminals and the plurality of load terminals. Second interrupting contacts are disposed between at least one of the plurality of receptacle load terminals and at least one of the plurality of feed-through load terminals. The second interrupting contacts are initially disposed in an open state. The second interrupting contacts are closed in response to the plurality of line terminals being coupled to a source of AC power. At least one fault condition is sensed in the electric circuit. A fault condition signal is generated in response to the step of sensing. The first interrupting contacts are tripped in response to the fault condition signal, whereby the plurality of line terminals are decoupled from the plurality of load terminals. 
   Additional features and advantages of the invention will be set forth in the detailed description which follows, and in part will be readily apparent to those skilled in the art from that description or recognized by practicing the invention as described herein, including the detailed description which follows, the claims, as well as the appended drawings. 
   It is to be understood that both the foregoing general description and the following detailed description are merely exemplary of the invention, and are intended to provide an overview or framework for understanding the nature and character of the invention as it is claimed. The accompanying drawings are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification. The drawings illustrate various embodiments of the invention, and together with the description serve to explain the principles and operation of the invention. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a schematic of a protective device in accordance with one embodiment of the present invention; 
       FIG. 2  is a schematic diagram of a protective device in accordance with another embodiment of the present invention; 
       FIG. 3  is a plan view of a mechanical implementation of a miswire resistance circuit in accordance with the present invention; 
       FIG. 4  is a side view of a mechanical implementation of a miswire resistance circuit in accordance with another embodiment of the present invention; 
       FIG. 5  is a side view of the miswire circuit shown in  FIG. 4  in an open state; 
       FIG. 6  is a sectional view illustrating a receptacle miswire contact structure in accordance with an embodiment of the present invention; 
       FIG. 7  is the miswire contact structure depicted in  FIG. 6  in a closed state; 
       FIG. 8  is a sectional view illustrating a second receptacle miswire contact in an open state in accordance with the present invention; 
       FIG. 9  is the miswire contact structure depicted in  FIG. 8  in a closed state; 
       FIG. 10  is a sectional view illustrating a third receptacle miswire contact in an open state in accordance with the present invention; 
       FIG. 11  is the miswire contact structure depicted in  FIG. 10  in a closed state; 
       FIG. 12  is a sectional view illustrating a fourth receptacle miswire contact in accordance with the present invention; 
       FIG. 13  is a sectional view of an end-of-life mechanism in an operational state in accordance with the present invention; 
       FIG. 14  is the end-of-life mechanism depicted in  FIG. 13  is an end-of-life state; and 
       FIG. 15  is a schematic of a protective device in accordance with yet another embodiment of the present invention. 
   

   DETAILED DESCRIPTION 
   Reference will now be made in detail to the present exemplary embodiments of the invention, examples of which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or like parts. An exemplary embodiment of the protective device of the present invention is shown in  FIG. 1 , and is designated generally throughout by reference numeral  10 . 
   As embodied herein and depicted in  FIG. 1 , a schematic of a protective device in accordance with one embodiment of the present invention is disclosed. In particular,  FIG. 1  provides a schematic diagram of GFCI  10 . Device  10  includes a neutral line terminal  102  and a hot line terminal  104 . When device  10  is in service, these terminals are connected to an AC power source, e.g., the wiring connected to the distribution panel. Device  10  also includes a neutral feed through terminal  106  and hot feed through terminal  108 . These terminals provide electrical power to downstream, daisy-chained receptacles or switches that are often included in the branch circuit. Device  10  also includes neutral receptacle terminal  110  and hot receptacle terminal  112 . The receptacle terminals, of course, provide appliances equipped with corded plugs access to AC power. 
   The line terminals  102 ,  104 , are coupled to a sensor  130 , which in a GFCI, is typically a differential transformer. Sensor  130  is coupled to detector circuit  132 . When differential transformer  130  senses a differential current, i.e., unequal amounts of current flowing in the hot and neutral conductors, due to a ground fault condition, detector  132  provides a fault detection signal on an output line. The output is coupled to silicon controlled rectifier (SCR)  133 . SCR  133  is configured to be turned ON by the fault detection signal. SCR  133  is further coupled to solenoid  122 . When SCR  133  conducts, solenoid  122  is energized. Solenoid  122  includes an armature. When solenoid  122  is energized the armature actuates circuit interrupter  120 . Circuit interrupter  120  electrically decouples the line terminals from the load terminals in response thereto. 
   In particular, when solenoid  122  magnetically actuates the armature, circuit interrupter  120  displaces bus bars  124  and  126  to open the contacts. This is commonly referred to as the tripped position. In the tripped position, air gaps  125  and  127  are introduced when the receptacle load terminals  110 ,  112  and feed through load terminals  106 ,  108  are disconnected from line terminals  102 ,  104 . Of course, this interrupts the flow of hazardous current through the fault condition. 
   In the embodiment shown in  FIG. 1 , a manual reset button  128  is coupled to circuit interrupter  120 . When the reset button  128  is depressed, bus bars  124  and  126  are driven into a reset state, reconnecting the load terminals  106 ,  108  and the receptacle terminals  110 ,  112  to the line terminals  102 ,  104 . In the reset state, the air gaps  125  and  127  are eliminated. 
   It will be apparent to those of ordinary skill in the pertinent art that modifications and variations can be made to circuit interrupter  120  of the present invention depending on cost and size considerations. For example, circuit interrupter  120  may include bus bars, cantilever beams, or any other suitable structure. Circuit interrupter  120  may also be a solid state device that is tripped or reset electronically and that interrupts load current by way of semiconductor switches. 
   In one embodiment, device  10  is periodically tested by a circuit that automatically establishes a periodical simulated fault condition. Reference is made to U.S. Pat. No. 6,674,289, patent application Ser. No. 10/668,654, patent application Ser. No. 10/758,530, and patent application Ser. No. 10/868,610, which are incorporated herein by reference as though fully set forth in its entirety, for a more detailed explanation of various embodiments of the automatic test circuit. 
   In another embodiment, as shown in  FIG. 1 , device  10  may be tested by operating a manual test button  134 . When depressed, test button  134  generates a simulated fault condition. The test result may be displayed by a visual or audible indicator  136 . A successful test result may also be indicated by movement of reset button  128 . In particular, the test is conducted to determine whether the fault circuitry and/or the circuit interrupter is responsive to a fault. Accordingly, reset button  128  is configured to move from a reset position to a tripped position in response to a successful test. 
   In another embodiment, if the device is already in a tripped state and the test is unsuccessful, device  10  prevents circuit interrupter  120  from being reset, and/or being able to maintain a reset condition. If the device is reset by the user, it will immediately trip thereafter. 
   A miswire circuit is coupled between line terminals  102  and  104 . The miswire circuit includes a fault resistance  138  that is designed to generate a difference current in excess of a predetermined fault threshold. The fault threshold typically exceeds the level of differential current that the GFCI has been designed to interrupt, typically 6 milliamperes. The miswire resistance  138  is on the line side of circuit interrupter  120  and electrically coupled to line terminals  102  and  104 . When the GFCI  10  is both tripped and miswired, i.e., when power is supplied to the load terminals, nothing visible happens, but there is no power to the receptacle terminals  110 ,  112 . 
   If the GFCI is in the reset condition, it will immediately trip when power is applied to the load side. Further, the device will trip before miswire resistance  138  opens because the current flowing through the miswire resistance  138  is interrupted when the device trips. The estimated time it takes for the miswire resistance  138  to “clear,” or burn out, is greater than 50 ms. The trip time of the GFCI is less than or equal to 25 ms. If one attempts to reset the device when in the miswired condition, the device repeatedly trips out until such time as the device is wired correctly. GFCI  10  will not operate until the device is properly wired. 
   On the other hand, when electrical power is connected in a correct manner to the line terminals, a differential current is created by the miswire resistance  138 . If the device is reset before power is applied, the device trips as a result of this differential current. If the device is already in the tripped condition before power is applied, nothing visible happens. However, because the miswire resistance is on the line side of the circuit interrupter  120 , current through fault resistance  138  continues to flow, regardless of whether the circuit interrupter  120  is in the tripped condition. As noted previously, the current through miswire resistance  138  causes the resistance to clear itself in a short time, typically 50 ms to 5 seconds. This can be accomplished by selecting a resistor or resistors whose power rating is greatly exceeded by the current. 
   In an alternate embodiment, a fuse  148  is provided in series with the miswire resistance  138 . The fuse is characterized by a properly selected I 2 t rating such that the fuse blows instead of the miswire resistance  138 . Once the device has been properly wired with power connected to the line terminals and the fault has been cleared, device  10  may be reset and provide its normal protective functions. 
   An interesting issue with respect to miswire protection relates to performing Underwriters Laboratories required tests, such UL-943, during the manufacture of the protective devices. The differential current produced by the miswire resistance  138  must not affect the test results, or cause the miswire resistance to clear in the manner previously described. One solution is to place a normally closed switch  140  in series with the miswire resistance  138 . 
   With regard to the mechanical implementation of switch  140 , switch  140  may be implemented using a flexible conductive spring arm that normally rests against a contact on the top side of a printed circuit board. A hole is disposed in the printed circuit board directly below the spring arm of switch  140 . An additional hole is disposed below the first hole in the plastic back body of the GFCI device. When GFCI  10  is inserted into the test equipment to perform the aforementioned manufacturing tests, a mechanical test probe engages the spring aim of switch  140  through the two aforementioned holes. The probe causes the spring arm of switch  140  to be pushed away from the contact to open the differential current circuit path. Manufacturing testing may be performed without clearing miswire resistance  138 . The last test performed on the GFCI device in the test sequence is to disengage the probe from the spring arm of switch  140 . The differential current circuit path is reconnected to check the integrity of the differential current circuit path and other GFCI components. The reconnected path should cause the GFCI device to trip if it is operating properly. 
   In traditional protection devices, the circuit interrupter denies power to the line terminals from the feed-through terminals. However, the denial of power to the feed-through terminals does not guarantee that the miswired condition will be corrected by the installer. For example, the electrical distribution system may not include a daisy chained receptacle or switch, in which case the feed-through terminals are not used. While the traditional device may disconnect the line terminals from the load terminals, it is not configured to disconnect the receptacle load terminals from the feed-through load terminals. As such, traditional devices expose users to possible hazardous conditions when miswired. Thus there is a need to protect a user from a fault condition in the user attachable load even when the protective device has been miswired. 
   In the present invention the need is addressed by interposing miswire contacts  152 ,  154  between the hot feed-through terminal  108  and hot receptacle terminal  112 , respectively. Contacts  152 ,  154  are configured to electrically disconnect the hot feed-through terminal  108  and hot receptacle terminal  112  when device  10  is miswired. Thus, power to a fault condition in the user attachable load is cut off by contacts  152 . Once the miswired condition has been corrected, miswiring contacts  152  are configured to close, to thereby establish electrical connection between the load terminals  106 , 108  and receptacle terminals  110 ,  112 . In another embodiment, only contact  152  is implemented between the hot load contact and the hot receptacle contact. Miswire contacts  152 ,  154  may be implemented using any suitable type of contacts, including a mechanical contact arrangement, a solid state contact arrangement, or any of the other miswire contact arrangements disclosed herein. 
   However, the use of both contacts provides more protection because contact  154  serves to protect the user from a fault condition in the user attachable load when the voltage source has been miswired to the feed-through terminals and when the hot and neutral conductors from the voltage source have been transposed. When the conductors are transposed, the shock (or fire) hazard shifts from receptacle hot load terminal  112  to receptacle neutral load terminal  110 . The contact pair  152 ,  154  protect the user regardless of how the power source has been wired to the feed-through terminals. In yet another embodiment, contacts  154  are included but contacts  152  are not included. This embodiment also denies power to the user attachable load when the device has been miswired. The denial of power motivates the user to correct the miswired condition before a fault condition in the user attachable load is likely to take place. 
   Referring back to  FIG. 1 , the circuit includes resistors  142 , 144 , 146 , and indicator light  136 . Light  136  is a trip indication light. The light is off if GFCI  10  is in the reset condition, and illuminates if the GFCI  10  is tripped. If device  10  is miswired, light  136  is off, regardless of whether the device is reset or tripped. If device  10  is properly wired, allowing a reset condition to be maintained, light  136  is off. If device  10  is properly wired and tripped, light  136  is illuminated. Light  136  may also serve to notify the user that the solenoid-driving device is defective and that device  10  is no longer operational. Light  136  may be replaced by an audible device. As such, the present invention may include a visual and/or audible indicator. The indicator may have multiple indication meanings. 
   The indicating circuit operates as follows. When the device  10  is wired properly, and the device is reset, light  136  is off. The circuit interrupter  120  is closed (reset) and no voltage is present across light  136  and resistor  144 . If the GFCI trips for any reason, light  136  is energized by line voltage being applied across light  136  and resistors  144  and  142 . When the circuit interrupter  120  is reset, voltage is removed and light  136  turns off. If the device is miswired, light  136  is off when the circuit interrupter  120  is reset. However, when the device trips in this condition, there is no return path to neutral through resistor  142 . Accordingly, light  136  does not turn on as it would if the GFCI were wired properly. This feature is not dependent on the miswire resistance  138 . Thus, if the miswire detection circuit has been previously used and the miswire resistance cleared, miswire detection is still possible by energizing light  136  in conjunction with tripping the GFCI  10 . 
   Turning now to end-of-life indication, the circuit branch that includes resistor  146  is used to indicate that SCR  133  (i.e., the solenoid driving device) is defective. When SCR  133  short circuits, a current path to supply neutral is established via resistor  146  to thereby energize light  136 . Note that trip solenoid  122  will open within a few seconds if the line voltage is continuously applied to it. This is exactly the outcome when SCR  133  short circuits. If solenoid coil  122  burns out, device  10  may no longer be tripped after being reset. On the other hand, light  136  remains energized, indicating a defective solenoid driving device. The value of resistor  146  must be kept low relative to the value of resistor  144 , since the two resistors form a voltage divider that limits the voltage across light  136 . If light  136  is a neon lamp, the values of resistors  144  and  146  are chosen to apply about 60 volts. This voltage level allows the lamp to arc and energize. In this embodiment, resistor  146  is typically 33 K. This resistance value results in approximately 66 volts being applied across the neon lamp at a worst case line voltage of 102 VAC. 
   To summarize the switch states, when device  10  is wired properly and reset, indicator  136  is OFF. When device  10  is wired properly and tripped, indicator  136  is ON. When an end-of-life condition occurs, indicator  136  is ON in the reset state. Finally, when device  10  is miswired and tripped, indicator  136  will be OFF. 
   As embodied herein and depicted in  FIG. 2 , a schematic diagram in accordance with another embodiment of the present invention is shown. Protective device  200  is a general diagrammatic depiction of a protective device in that it may be applied to various protective devices such as ground fault circuit interrupters (GFCIs), arc fault circuit interrupters (AFCIs), or combination devices that provide both AFCI and GFCI protection. The present invention should not be construed as being limited to the examples listed above. Thus, protective circuit  202  may be configured to detect any number of fault conditions, including ground faults, arc faults, or both. The protective circuit  202  may include self-diagnostics for detecting an end-of-life condition in the circuit  202  and/or circuit interrupter  206 . 
   As shown in  FIG. 2 , protective circuit  202  is coupled between the line terminals  102 ,  104 . The output of the protective circuit is coupled to SCR  204 . Solenoid  208  is disposed between SCR  204  and the hot line conductor. The miswire detection circuit, including miswire resistor  138 , is disposed in parallel to solenoid  208 . Solenoid  208  is, in turn, coupled to interrupting contacts  210 , in the manner previously described. During operation, protective circuit  202  provides SCR  204  with a fault detection signal. SCR  204  begins to conduct to thereby energize solenoid  208 , causing the circuit interrupter  206  to trip contacts  210 . As a result, load terminals  106 ,  108 ,  110 , and  112  are disconnected from line terminals  102 ,  104 . Of course, the circuit interrupter  206  may be implemented using bus bars, cantilevers or other similar structures configured to form an air gap, or by turning off one or more solid state switch. 
   Resistors  142 ,  144 ,  146 , and light  136  are similar to, and have the same functionality as, the circuits depicted in  FIG. 1 . However, the miswire circuit in  FIG. 2  operates in a different manner by directly signaling SCR  204 . If device  200  is in the reset state and power is miswired to the load terminals, current flows through normally closed switch  140 , fuse  148 , miswire resistance  138  to cause SCR  204  to activate solenoid  208 . Interrupting contacts  210  are opened and device  200  is tripped. Fuse  148 , if provided, and miswire resistance  138  are chosen to withstand the current flow for the time that power is applied to the load terminals to the moment when interrupting contacts  210  open, which is approximately 25 milliseconds. If line power is connected as intended to the line terminals of the protective device, current flows through normally closed switch  140 , fuse  148 , miswire resistance  138 , and SCR  204  until such time as resistance  138  clears, or fuse  148  (if provided) clears. Afterwards, device  200  may be reset. 
   Accordingly, the miswire detection functionality of the circuit shown in  FIG. 2  differs from the miswire protection circuit in  FIG. 1  in that the miswire detection signal does not necessarily have to be routed through the fault detection circuitry. The fault detection circuit of  FIG. 1  evaluates the miswire detection signal as it would a fault condition signal. On the other hand, the miswire detection signal of  FIG. 2  by-passes the fault detection circuit and is applied directly to SCR  204 . In another embodiment, the miswire detection signal is gated with the fault detection signal to create a Boolean output that is interpreted by detection circuitry. 
   Solenoid  208  is designed not to burn out during the interval that SCR  204  is turned ON. The interval is typically on the order of approximately 100 milliseconds. Accordingly, the miswire protective functionality described in the embodiment shown in  FIG. 1  is provided without necessarily requiring a differential current transformer  130  to detect the miswired condition. Further, neither the miswire resistance nor the fuse circuit need be attached to both the hot and neutral line conductors. If an electronic switching device other than an SCR is used, e.g., a bipolar transistor, the connection to the gate of the SCR would instead be made to the base of the bipolar transistor. 
   The miswire resistance  138  or fuse  148  (if provided) are susceptible to damage from lightning storms and types of loads that impose voltage impulse transients on the electrical distribution system. The susceptibility may be eliminated by electrically coupling a metal oxide varistor (MOV)  212  across the line terminals. There are many alternate methods for suppressing voltage transients. Reference is made to U.S. patent application Ser. No. 10/964,217 and the U.S. Patent Application corresponding to Ser. No. 11/080,574, which are incorporated herein by reference as though fully set forth in its entirety, for a more detailed explanation of alternate methods for suppressing voltage transients. 
   As previously described, contacts  152  and/or  154  serve to protect the user from a fault condition in the user attachable load. The contacts are configured to open in response to a miswire condition. The contacts are configured to close (or be closeable) if the protective device has been properly wired. 
   Referring to  FIG. 3 , a plan view of the miswire resistance circuit  300  is shown. Circuit  300  includes at least one heating device such as resistor  302  in combination with wire  304 . Wire  304  has a predetermined melting point. When device  10  is properly wired, resistor  302  produces I 2 R heating. When the temperature rises above the pre-determined threshold, wire  304  melts and an air gap is formed. The air gap is configured to block surge currents resulting from impulse voltages. It will be apparent to those of ordinary skill in the pertinent art that modifications and variations can be made to wire  304  of the present invention depending on the desired temperature threshold and the value of the resistance chosen. Accordingly, wire  304  may be of any number of alloys familiar to those skilled in the art, including tin/lead alloys. 
   Referring to  FIG. 4  and  FIG. 5 , a second mechanical implementation of the miswire circuit is shown.  FIG. 4  is an elevation view of miswire circuit  400  in a closed state. Miswire circuit  400  includes at least one heating resistor  402  coupled to a spring member  404  by connective element  408 . Connective element  408  may be implemented using solder, or some other similarly conductive alloy. Spring member  404 , solder  408 , and miswire resistor  402  are electrically continuous in a closed state. Of course, connective element  408  is designed to have a predetermined melting threshold. When device  10  is properly wired, resistor  402  produces I 2 R heating. When the temperature rises above the pre-determined threshold, connective element  408  melts, spring member  404  is released, and an air gap  410  is formed. 
     FIG. 5  is an elevation view of the miswire circuit  400  depicted in  FIG. 4  in an open state. As alluded to above, once the solder attachment  408  fails, spring  404  opens to a pre-biased position to form an air gap  410 . 
     FIG. 6  is a sectional view illustrating a receptacle contact structure  152  in accordance with an embodiment of the present invention. While  FIG. 1  shows two receptacle contacts  152 ,  154 ,  FIG. 6  only shows one such contact structure ( 152 ) for ease of illustration. A duplicate structure may be implemented to form contact  154 . 
     FIG. 6  shows the receptacle contacts  152  in an open state. Referring back to  FIG. 1 , contacts  152  disconnect the hot feed-through terminal  108  and hot receptacle terminal  112  until device  10  is wired properly. Thus, the implementation shown in  FIG. 6  eliminates any potentially hazardous condition caused by a miswire condition. Once the miswired condition has been corrected, miswiring contacts  152 ,  154  are configured to close, to thereby establish electrical connection between the load terminals  106 ,  108  and receptacle terminals  110 ,  112 . 
   Referring back to  FIG. 6 , miswire circuit  600  includes at least one heating resistor  602  coupled to arm  606  by way of connective element  604 . Connective element  604  may be implemented using solder, or a connective element formed from a similarly conductive alloy. Miswire contacts  152  include a movable contact  1520  and a fixed contact  1522 . Movable contact  1520  is disposed on spring member  608 . Spring member  608  is coupled to circuit board  610 . Arm  606  extends through a hole  612  formed in circuit board  610 . At one end, arm  606  is fixedly attached to circuit board  610  by connective element  604 . At the other end, arm  606  is connected to spring member  608 . Accordingly, resistor  602 , connective element  604 , arm  606 , spring member  608 , and movable contact  1520  are electrically continuous. However, power is denied to the receptacles because of the air gap disposed between movable contact  1520  and fixed contact  1522 , i.e., miswire contacts  152  are in an open state. 
     FIG. 7  is the miswire contact structure depicted in  FIG. 6  in a closed state. In other words, once the installer properly wires device  10  such that the line terminals are connected to the AC power source (i.e., the wiring from the distribution panel), current begins to flow through resistor  602  generate I 2 R heating in the manner previously described, causing the temperature of connective element  604  to exceed a predetermined temperature threshold. Once the connective element fails, arm  606  is released, and becomes slidable. Because spring member  608  is biased toward the closed state, arm  606  moves in the direction shown to close contacts  152 . Once contacts  152  have closed, miswire resistance  602  is configured to open. Opening may be accomplished by clearing fuse  148  ( FIGS. 1 ,  2 ), clearing resistor  602 , or failure of solder attachment  604 . 
     FIG. 8  is a sectional view illustrating a receptacle contact structure  152  in accordance with an alternate embodiment of the present invention. In this embodiment, miswire circuit  800  includes at least one heating resistor  802  and a spring member  806  that is fixedly attached near, or to, one lead of resistor  802  using solder element  804 . As noted above, the solder connection may be replaced by any suitable means for releasably attaching spring  806  to resistor  802 . For example, solder element  804  may be replaced by a similarly conductive alloy. As shown by  FIG. 8 , resistor  802 , connective element  804 , spring member  806 , and movable contact  1520  are electrically continuous. On the other hand, an air gap exists between fixed contact  1522  and movable contact  1520 . Accordingly, power is denied to the receptacles  110 ,  112  ( FIG. 1 ) because device  10  has not been properly wired. 
     FIG. 9  shows the mechanical implementation depicted in  FIG. 8  in a closed state. Once the installer properly wires device  10  such that the line terminals are connected to the AC power source (i.e., the wiring from the distribution panel), current begins to flow through resistor  802  generate I 2 R heating in the manner previously described, causing the temperature of connective element  804  to exceed a predetermined temperature threshold. Once the connective element  804  fails, spring  806  is released. Spring member  806  is biased toward the closed state and moves to close contacts  152  once released, foaming air gap  808 . 
     FIG. 10  is an alternate embodiment of a receptacle miswire contact structure. Miswire circuit  1000  includes at least one heating resistor  1002  attached using solder  1004 , or a similarly conductive alloy. Resistor  1002  is mechanically coupled to plunger  1008 . Plunger  1008  extends from resistor  1004  through a hole in board  1020 . Plunger  1008  is coupled to buss bar  1006 . Spring member  1010  exerts a biasing force against bus bar member  1006 . However, plunger  1008  is fixed in place by solder  1004  such that contacts  152  are open. When the protection device is properly wired, the solder attachment  1004  fails in the manner previously described. 
     FIG. 11  shows the receptacle miswire contact structure depicted in  FIG. 10  in a closed position. Again, Once device  10  is wired properly, current flows through resistor  1002  to thereby generate I 2 R heating of solder  1004 . Of course, the solder  1004  gives way when the temperature exceeds a predetermined temperature threshold. Once the solder fails, resistor  1002  is pushed out of position by the movement of plunger  1008 . Plunger  1008  is urged through the hole by the biasing force exerted by spring  1010 . The force applied by spring  1010  moves contacts  152  into the closed state. 
   As noted previously, the embodiments provided above have been described with respect to hot conductor contacts  152 . However, the structures disclosed herein are equally applicable to neutral conductor contacts  154 . 
   As embodied herein and depicted in  FIG. 12 , yet another receptacle miswire contact arrangement in accordance with the present invention is disclosed.  FIG. 12  is employs a single miswire circuit  1200  to couple both hot and neutral miswire contacts  152 ,  154  to their respective conductive paths. Miswire circuit  1200  includes at least one heating resistor  1202  attached using solder  1204 , or some other similarly conductive alloy. Solder  1204  and miswire resistor  1202  are electrically continuous and therefore conduct electricity. Hot contact  152  and neutral contact  154  are disposed on movable arms  1212 ,  1214 . Latch block  1208  is constructed of an electrically non-conductive material. Latch block  1208  is constrained between resistor  1202  and arms  1212 ,  1214 , forcing contacts  154  and  152  into an open state. When the protection device is properly wired, the solder attachment  1204  fails, causing the resistor to give way. The force applied by spring  1210  moves contacts  152  and  154  into the closed state. In an alternate embodiment, arms  1212  and  1214  are spring members. In this embodiment, spring  1210  is not required. Of course, spring members  1212  and  1214  are pre-biased to close contacts  154  and  152  after solder attachment  1204  has failed. 
   In another embodiment, the body of fuse  148  may be used to capture latch block  1208  (or arm  1008 .) After device  10  has been properly wired, the clearing of fuse  148  permits motion of the latch block (or arm) to close the miswire contacts. 
   Referring to  FIG. 13 , an end-of-life mechanism  1300  is depicted. Mechanism  1300  is configured to permanently disconnect the power source form the load terminals when device  10  is experiencing an end-of-life condition that would prevent device  10  from interrupting a predetermined fault condition. End-of-life conditions include one or more of the following: a failure in sensor  130 , detector  132 , SCR  133 , or circuit interrupter  120 . 
   Mechanism  1300  includes end-of-life contacts  1302 , 1316 , that are operated essentially in a different manner than miswire contacts, e.g., contacts  1302 ,  1316  are in the closed state at the time of installation and throughout the life of the product and are configured to open when an end-of-life condition has occurred. Contacts  1302 ,  1316  are disposed in series with circuit interrupter  120  (refer to  FIG. 1 .) Mechanism  1300  includes at least one heating resistor  1304  attached using solder  1306 , or another similarly conductive alloy. Solder  1306  and resistor  1304  share electrical continuity, and therefore are in a conductive state. Contacts  1302  are connected to bus bar  1308 . Spring  1310  is constrained between resistor  1304  and bus bar  1308  to close contacts  1302 . 
     FIG. 14  is an elevation view of the end-of-life mechanism depicted in  FIG. 13  in an end-of-life state. When the protection device reaches an end-of-life condition, current through the heating resistor  1304  begins to flow. The solder attachment  1306  fails once the temperature level exceeds the melting point of the solder. At that point resistor  1304  is pushed away by the action of spring  1312  and spring  1310 , which are no longer constrained by resistor  1304 . The force applied by spring  1312  moves contacts  1302  into the open state. Force applied by spring  1312  may also break electrical continuity to resistor  1304  by forming an air gap  1314 . 
   As noted above, the end-of-life mechanism described in  FIGS. 13 and 14  includes contacts  1302  that are disposed between the hot line and hot load terminals. In an alternate embodiment, another set of end-of-life contacts (not shown) are disposed between the neutral line and neutral load terminals in a manner similar to the arrangement shown in  FIG. 12 . Both sets of contacts ( 1302 , neutral path contacts) may be operated by a single resistor in a similar manner as has been described in  FIG. 12 . 
   Those of ordinary skill in the art will recognize that the end-of-life mechanism and miswire contacts described herein may both be included in device  10 . 
   As embodied herein and depicted in  FIG. 15 , a schematic of a protective device in accordance with yet another embodiment of the present invention is disclosed. The fault detection circuitry includes sensor  130  coupled to detector  132 . If a fault is present, detector  132  provides a fault detection signal to SCR  133  causing it to conduct. When SCR  133  conducts, solenoid  122  is energized causing its armature to actuate interrupting contact assembly  120 . 
   Device  10  also includes miswire contacts  902  and/or  904 . Miswire contacts  902 ,  904  disconnect the feed-through load terminals  108 ,  106  from the receptacle load terminals  112 , 110  respectively. Contacts  902 ,  904  are coupled to miswire solenoid  900 . When device  10  has been miswired, the source voltage from the electrical distribution system is connected to feed-through terminals  106 ,  108 . There is no voltage applied to solenoid  900  because contacts  902 ,  904  are in the open state. Since contacts  902 ,  904  cannot close until voltage is applied to solenoid  900 , the contacts remain in the open state. On the other hand, when device  10  is properly wired, voltage is applied to solenoid  900 , and solenoid  900  is energized causing contacts  902 ,  904  to close. The configuration results in permanent closure of contacts  902 ,  904 . The device may employ a magnetic latching device such as a permanent magnet or a mechanical latching device. Those skilled in the art will recognize that any suitable latching mechanism may be employed herein. 
   In an alternate embodiment, contacts  902 ,  904  re-open each time there is loss of source voltage on the line terminals. In this manner, the miswire detection feature is available each time device  10  is removed from the installation and re-installed. Another alternate embodiment includes miswire solenoids that are intended to be only momentarily connected to voltage. Such solenoids overheat if connected to a permanent voltage. The overheating problem is resolved by disposing contacts  906  in series with solenoid  900 . Contacts  906  are opened after contacts  903 ,  904  have successfully closed. Closure of contacts  906  may be accomplished by coupling them to solenoid  902  or to contacts  902 ,  904 . 
   Those skilled in the art will recognize that circuit interrupter  120  is constructed to reliably perform many trip/reset operations. In particular, device  10  is typically designed to perform 3,000 trip/reset cycles. On the other hand, miswire contacts  152   154  ( FIGS. 1 ,  2 ) and miswire contacts  902 ,  904  ( FIG. 15 ) may be actuated only a handful of times over the course of the operating life of device  10 . End-of-life contacts  1302 ,  1304  ( FIGS. 13-14 ) may be actuated only once—when the device reaches an end-of-life state. Accordingly, miswire contacts and end-of-life contacts may be implemented using a simpler construction. For example, circuit interrupter  120  may be implemented using silver rivets. Such rivets provide reliable operation for a few thousand trip/reset operations. As such, they may be omitted, and a simpler, less expensive construction may be employed to implement the miswire contact assembly and the end-of-life contact assembly. 
   It will be apparent to those skilled in the art that various modifications and variations can be made to the present invention without departing from the spirit and scope of the invention. Thus, it is intended that the present invention cover the modifications and variations of this invention provided they come within the scope of the appended claims and their equivalents.