Abstract:
The present invention is directed to an electrical wiring protection device that includes a housing assembly having a plurality of line terminals and a plurality of load terminals. A fault detection circuit is coupled to at least one of the plurality of line terminals and configured to generate a fault detection signal in response to detecting at least one fault condition in the electrical distribution system. A circuit interrupter assembly is coupled to the fault detection circuit. The circuit interrupter assembly is configured to couple the plurality of line terminals to the plurality of load terminals to form a conductive electrical path in a reset state, and decouple the plurality of line terminals from the plurality of load terminals in response to a fault detection signal in a tripped state. A voltage transient suppression circuit is connected between the plurality of line terminals, the voltage transient suppression circuit including a movistor differentially coupled relative to the at least one sensor circuit such that one lead of the movistor is coupled to a first line conductor disposed on a line side of the at least one sensor circuit and another lead of the movistor is coupled to a second line conductor disposed on a load side of the at least one sensor circuit. A movistor protection circuit is coupled in series to the movistor, the movistor protection circuit being configured to limit an amount of electrical energy applied to the movistor as a function of at least one electrical parameter.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This is a continuation of U.S. patent application Ser. No. 12/780,342 filed on May 14, 2010, which is a continuation of U.S. patent application Ser. No. 11/080,574 filed on Mar. 15, 2005, the content of which is relied upon and incorporated herein by reference in its entirety, and the benefit of priority under 35 U.S.C. §120 is hereby claimed. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates generally to electrical wiring devices, and particularly to protective wiring devices. 
         [0004]    2. Technical Background 
         [0005]    Electrical distribution systems that provide power to structures such as residences, commercial buildings or other such facilities typically include one or more breaker panels coupled to a source of AC power. Of course, the breaker panel distributes 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, the plug being insertable into the receptacle outlet. However, certain types of faults have been known to occur in various portions of the electrical distribution systems. Accordingly, electric circuit protection devices may be disposed throughout the distribution system, i.e., in the breaker panel and in protective devices having receptacle outlets. Protective devices may also be installed in the electrical load itself. 
         [0006]    Both receptacle wiring devices and electric circuit protective wiring devices may be 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 conductors that provides electrical power from the electrical distribution system. Load terminals are coupled to wiring that directs AC power to one or more electrical loads. Those of ordinary skill in the pertinent art will understand that the term “load” refers to an appliance, a switch, or some other electrically powered device. 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. The load terminals may also be connected to an electrically conductive path that is also connected to a set of receptacle contacts. The receptacle contacts 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 opening to thereby energize the device. 
         [0007]    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 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. 
         [0008]    When a device is installed, its line terminals are connected to an AC power source, such as a single phase 120 VAC AC power source. However, transient voltages may propagate in an electrical distribution system as well as the AC power signal. Further, the amplitudes of transient voltages are typically greater than the amplitude of the source voltage by at least an order of magnitude. Transient voltage pulses may be generated by any number of events. For example, transient voltages may be introduced into the distribution system by lightning. Transient voltages may also be generated when an inductive load is turned off, when a motor with noisy brushes is operated, or by other such load situations. 
         [0009]    Transient voltages are known to damage protective devices such that the device will cease to function as designed. This is sometimes referred to as an end of life condition. End of life failure modes include failure of device circuitry, the relay solenoid that opens the GFCI interrupting contacts, and/or the solenoid driving device, such as a silicon controlled rectifier. The damage may result in the protective device permanently denying power to the protected portion of the electric circuit. In this case, the user is forced to replace the protective device. Alternatively, the damage may result in the protective device still providing power to the load even though the device has become non-protective. In this case, the user is left unprotected after an end-of-life condition has occurred. Thus the user is either inconvenienced by having to change out the device, or even worse, he is left unprotected. 
         [0010]    Most devices include surge protection components. However, surge protection components occupy a considerable volume within the device housing. As a result, the overall size of the device is relatively large, making it harder to install the device within a wall box. Another problem is that surge protective components themselves are known to experience an end-of-life condition. If the surge protection component fails, the device is unprotected from damages due to transient voltages. 
         [0011]    Accordingly, a compact protective device that includes an improved space-conserving surge protection arrangement is needed that continues to afford protection after the occurrence of a voltage transient event on the electrical distribution system. The compact protective device must be configured to reliably protect the user from a fault condition in the electrical power distribution system. 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 
       [0012]    The present invention addresses the needs described above by providing a compact protective device that includes an improved space-conserving surge protection arrangement is needed that continues to afford protection after the occurrence of a voltage transient event on the electrical distribution system. The compact protective device of the present invention is configured to reliably protect the user from a fault condition in the electrical power distribution system. Further, the protective device of the present invention is equipped to decouple the load terminals from the line terminals in the event of an end of life condition. 
         [0013]    One aspect of the present invention is directed to an electrical wiring protection device that includes a housing assembly having a plurality of line terminals and a plurality of load terminals. A fault detection circuit is coupled to at least one of the plurality of line terminals and configured to generate a fault detection signal in response to detecting at least one fault condition in the electrical distribution system. A circuit interrupter assembly is coupled to the fault detection circuit. The circuit interrupter assembly is configured to couple the plurality of line terminals to the plurality of load terminals to form a conductive electrical path in a reset state, and decouple the plurality of line terminals from the plurality of load terminals in response to a fault detection signal in a tripped state. A voltage transient suppression circuit is connected between the plurality of line terminals, the voltage transient suppression circuit including a movistor differentially coupled relative to the at least one sensor circuit such that one lead of the movistor is coupled to a first line conductor disposed on a line side of the at least one sensor circuit and another lead of the movistor is coupled to a second line conductor disposed on a load side of the at least one sensor circuit. A movistor protection circuit is coupled in series to the movistor, the movistor protection circuit being configured to limit an amount of electrical energy applied to the movistor as a function of at least one electrical parameter. 
         [0014]    In yet another aspect, the present invention is directed to an electrical wiring protection device has a housing assembly including a plurality of line terminals and a plurality of load terminals. A fault detection circuit is coupled to at least one of the plurality of line terminals and configured to generate a fault detection signal in response to detecting at least one fault condition in the electrical distribution system. A circuit interrupter is coupled to the fault detection circuit. The circuit interrupter is configured to couple the plurality of line terminals to the plurality of load terminals to form a conductive electrical path in a reset state, and decouple the plurality of line terminals from the plurality of load terminals in response to the fault detection signal in a tripped state. A voltage transient suppression circuit is coupled to at least one of the plurality of line terminals. The voltage transient suppression circuit conducts a leakage current in the event of failure, wherein the voltage transient suppression circuit is configured such that the leakage current generates a signal simulating the at least one fault condition when the circuit interrupter is in the reset state. An auxiliary switch is coupled to the voltage transient suppression circuit. The auxiliary switch decouples the voltage transient suppression circuit from the plurality of line terminals when the circuit interrupter is in the tripped state. 
         [0015]    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. 
         [0016]    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 
         [0017]      FIG. 1  is a block diagram of an electrical wiring device in accordance with a first embodiment of the present invention; 
           [0018]      FIG. 2  is a perspective view of a line spark gap structure in accordance with one embodiment of the present invention; 
           [0019]      FIG. 3  is a perspective view of a load spark gap structure in accordance with another embodiment of the present invention; 
           [0020]      FIG. 4  is a sectional view of the device depicted in  FIG. 1 ; 
           [0021]      FIG. 5  is a circuit diagram of a GFCI embodiment in accordance with the present invention; and 
           [0022]      FIG. 6  is a partial schematic diagram of a protective device in accordance with another embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0023]    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 wiring device of the present invention is shown in  FIG. 1 , and is designated generally throughout by reference numeral  10 . 
         [0024]    As embodied herein, and depicted in  FIG. 1 , a block diagram of an electrical wiring device  10  in accordance with a first embodiment of the present invention is disclosed.  FIG. 1  is a general protection device in that detector  40  may be configured as a GFCI detector, a GFEP detector, an AFCI detector or a combination thereof. In other words, the teachings of the present invention are applicable to each type of protective wiring device. 
         [0025]    The protective device  10  includes neutral line terminals  20  and hot line terminal  22  which are employed to connect device  10  to a source of AC power, i.e., to the distribution wiring connected to the breaker panel. The electrical distribution system may distribute power using single phase, split phase or multiple phase configurations by using two or more conductors. The wiring device  10  shown in  FIG. 1  is configured for single phase distribution. Device  10  also includes neutral load terminal  24  and hot load terminal  26  that are used to connect device  10  to load  28 . Line terminals  20 ,  22  are coupled to load terminals  24 ,  26  by the interruptible conductive path that includes neutral line conductor  12  and hot line conductor  14 . Neutral line conductor  12  and hot conductor  14  pass through sensor assembly  32  and terminate at circuit interrupter contacts  50 . The interruptible conductive path also includes neutral load conductor  16  and hot load conductor  18 , which are connected to load terminals  24 ,  26 , respectively. A test circuit  400  is coupled between neutral line conductor  12  and hot load conductor  18 . 
         [0026]    During normal operations when no fault is present, the contacts  50  are closed and AC power is provided to load  28  in the reset state. Generally speaking, sensor assembly  32  is coupled to fault detector  40 . Fault detector  40  is coupled to SCR  44 . SCR  44  energizes the trip solenoid  46  when it is in a conducting state. In turn, the trip solenoid  46  drives trip mechanism  48 . When trip mechanism  48  is activated, contacts  50  are opened. The device may be driven from the tripped state to the reset state by pushing reset button  52 . 
         [0027]    If device  10  includes GFCI protection, sensor assembly  32  is configured to sense the differential current flowing through the conductors  12 ,  14 . When device  10  provides power to a load  28  under normal conditions, the differential current in the conductors  12 ,  14  is zero. In other words, the currents to and from the load are equal in magnitude and opposite in polarity. However, when a ground fault ( 30 ) is present, a hot conductor in load  28  is coupled to ground. While the current through the hot conductor is sensed by sensor assembly  32 , the return current is diminished because the current flowing through the ground fault  30  flows to ground instead of returning through sensor assembly  32 . Thus, the differential current is not zero. If the differential current exceeds a predetermined amount, detector  40  provides a fault signal on detector output line  41 . 
         [0028]    As those skilled in the art will recognize, differential transformer  34  senses differential current via the magnetic field induced by the current flowing through conductors  12 ,  14 . In particular, conductors  12 ,  14  pass through the aperture of a toroidal core  36 . A non-zero current (differential current) in the conductors induces a magnetic flux in core  36  to induce a signal in winding  38 . Depending on the type of protective device, sensor assembly  32  may include additional sensors (not shown) such as current transformers, shunts, voltage dividers, additional toroidal transformers and the like. Such sensors are chosen to sense the fault condition(s) of interest. Signal from winding  38  and from other sensors that may be included in the sensor assembly  32  are provided to detector  40 . 
         [0029]    As noted above, detector  40  determines whether the signal from sensor assembly  32  represents a fault condition. If a fault condition is detected, detector  40  provides a signal to solid state switch  44  to energize solenoid  46 . Solenoid  46  in turn actuates trip mechanism  48  to open circuit interrupting contacts  50 . Interrupting contacts  50  disconnect at least the hot load terminal  26  from the hot line terminal  22 , but may also serve to disconnect the neutral load terminal  24  from neutral line terminal  20 . Either way, device  10  is tripped. 
         [0030]    Current stops flowing through the fault  30  when the device  10  trips. With power to the fault removed, detector  40  can no longer provide a fault detect signal to solid state switch  44 . Solid state switch  44  turns off and solenoid  46  is de-energized. The interval of time between the instant solenoid  46  energizes to trip the circuit interrupter, and the time it de-energizes after the fault condition is successfully eliminated, is typically less than 25 milliseconds. In the embodiment depicted in  FIG. 1 , solenoid  46  is implemented using a miniaturized construction because it does not have to be sized to withstand the heat that would be generated if the solenoid were continuously energized. 
         [0031]    As noted above, transient voltages are known to damage protective devices such that the device will cease to function as designed. Device  10  may be protected from high voltage transients by connecting a metal oxide varistor (MOV)  54  across the line and/or load terminals to clamp the transient voltage to a predetermined threshold. Of course, the predetermined voltage threshold is calculated such that device  10  survives the transient event. However, when employing this means for providing transient protection, MOV  54  must be relatively large in size to effectively clamp the transient voltage to an appropriate threshold. MOV  54  may be greater than 12 mm in diameter. As might be expected, a 12 mm MOV is usually relatively costly. 
         [0032]    Accordingly, one transient protection feature of the present invention includes the use of a MOV  56  in combination with an inductive component, such as solenoid  46 . Voltage transients typically have an amplitude of 1 to 6 kV. Because they are relatively brief in duration, they have frequency components that may be greater than 100 kHz. On the other hand, the impedance of solenoid  46  is typically greater than 500 Ohms at a frequency of 100 kHz. Thus, the frequency dependence of the coil impedance may be used to safeguard MOV  56 . Accordingly, MOV  56  may be downsized to take advantage of the frequency dependence of the coil impedance. In other words, MOV  56  may have a diameter that is less than or equal to 7 mm, while still managing to clamp the voltage at an appropriate threshold, because the solenoid impedance limits the amount of current through MOV  56 . This approach may also provide cost benefits as well. A smaller MOV is relatively inexpensive when compared to a larger MOV. Further, the life expectancy of MOV  56  may be greatly increased by the impedance of solenoid  46  because it restricts the amount of current through the MOV for a given voltage transient magnitude. However, it is still possible for MOV  56  to experience an end-of-life condition. 
         [0033]    An end-of-life condition may occur if the magnitude of the voltage transient is large enough. An end-of-life condition may also occur if there are a large number of voltage transients. Environmental stresses may also play a part in causing a failure. Whatever the cause, at end-of-life, a MOV becomes increasingly resistive in nature. If the resistance of MOV  56  is less than about 100 Ohms, solenoid  46  is sufficiently coupled to the power source to actuate trip mechanism  48  to open interrupting contacts  50 . The current flowing through the resistance of MOV  56  would also be conducted through solenoid  46 . The current, if uninterrupted, would cause solenoid  46  to burn out. 
         [0034]    The present invention includes an auxiliary switch mechanism to avoid solenoid burn-out. An auxiliary switch  58  is disposed in series with solenoid  46 . Auxiliary switch  58  is coupled to the trip mechanism  48 , or alternatively, to the interrupting contacts  50  such that the contacts of auxiliary switch  58  open when the circuit interrupter is in the tripped condition. Device  10  may be reset by manually actuating reset button  52 . This also results in the contacts of auxiliary switch  58  being closed. Upon reset, solenoid  46  is again coupled to the power source by way of the resistance of MOV  56 , and again, trip mechanism  48  opens contacts  50  as well as the contacts of auxiliary switch  58 . In sum, when MOV  56  has reached end-of-life, solenoid  46  is only momentarily energized. Solenoid  46  actuates the trip mechanism each time a reset action attempt is repeated. Even though MOV  56  has experienced an end-of-life condition, device  10  maintains its protective functionality. There is one caveat, however. 
         [0035]    If the end-of-life resistance of MOV  56  is greater than 100 Ohms, solenoid  46  may not be sufficiently coupled to the voltage source to trip the interrupting mechanism  48 . If the interrupting mechanism does not trip, the current through solenoid  46  will not be interrupted by auxiliary switch  58 . The uninterrupted current through solenoid  46  might cause the solenoid to burn out. 
         [0036]    Referring to dashed line  101 , in an alternate embodiment MOV  100  may be included to protect device  10  from a high voltage transients. Unlike MOV  56 , MOV  100  prevents solenoid burn-out for all end-of-life resistance values. Note that MOV  100  is connected in series with solenoid  46 . Thus, it is protected by the impedance of solenoid  46  in a similar manner to what has been described for MOV  56 . However, because of the series combination of MOV  100  and solenoid  46 , the current flowing through the series combination creates a differential current in the conductors passing through differential transformer  34 . Detector  40  responds to the differential current and causes the device to trip in the manner previously described. The predetermined threshold for a GFCI is typically 6 mA, and for a GFEP or AFCI is typically 30 mA. Should the end-of-life resistance of MOV  100  generate a current greater than the detection threshold in detector  40 , device  10  will trip and auxiliary switch  58  will open to protect solenoid  46  from burnout. 
         [0037]    Of course, if the current flowing through the series combination of MOV  100  and solenoid  46  are less than the detection threshold, device  10  will not trip. However, solenoid  46  is configured to be able to withstand the continuous flow of current of this magnitude. By way of illustration, if MOV  100  has a resistance that is less than about 4,000 Ohms, a device having a 30 mA detection threshold will trip, because the current generated will be greater than the threshold. On the other hand, as MOV  100  becomes more resistive, i.e., the resistance becomes greater than about 4,000 Ohms; the current generated is less than the differential current threshold and device  10  will not trip. However, solenoid  46  is configured to withstand current that is less than the detection threshold. Accordingly, solenoid  46  will not burn out in either scenario because the voltage transient circuit is coupled to the fault detector and generates a differential current which in turn causes the protective device to trip. The protective device of the present invention is both safe and reliable in the face of an end-of-life condition. 
         [0038]    Another feature of the present invention relates to preventing device  10  from being tripped by brief signals from sensor  32  that arise during voltage transient events. In particular, low pass filter  102  may be disposed between detector output  41  and SCR  44 . Filter  102  is configured to filter out the momentary currents that flow through MOV  100  to prevent solid state switch  44  from responding to voltage transient events. As a result, trip mechanism  48  is not nuisance-actuated by these voltage transient events. In an alternative embodiment, low pass filter  102  may be implemented in detector  40  to avoid using discrete components. 
         [0039]    Another feature of the present invention provides spark gaps ( 200 ,  300 ) for the absorption of the energy from the most severe transients. For example, voltage transients due to lightning have been known to produce 10 kV and/or 10 kA. The spark gaps are disposed in device  10  such that the surge current passing through the spark gap does not generate an output signal from sensor assembly  32 . In other words, the spark gap(s)  200 ,  300  are configured such that the discharge current is not manifested as a differential current that may possibly be sensed by transformer  34 . Spark gaps  200 ,  300  allow protective device  10  to remain in an operational condition in the presence of extremely severe voltage transients, or the currents that result from such voltage transients. 
         [0040]    Referring to  FIG. 2 , a perspective view of device  10  is shown that illustrates a spark gap structure  200  in accordance with the present invention. Spark gap structure  200  is disposed between the line terminals  20 ,  22 , and under sensor assembly  32 . The contact assembly  50  is implemented by movable contacts  206 ,  208  and fixed contacts  210 ,  212 . In particular, cantilever member  202  is connected to line neutral terminal  20  and cantilever member  204  is connected to line hot terminal  22 . Movable contacts  206 ,  208  are disposed at the distal ends of cantilever beams  202 ,  204 , respectively. Load terminals  24 ,  26  are electrically connected to fixed contacts  210 ,  212 . Trip mechanism  48  is configured to move contact pairs ( 206 ,  210 ) and ( 208 ,  212 ) into electrical connection when device  10  is reset and to move them out of electrical connection when device  10  is tripped. 
         [0041]    Spark gap structure  200  is an electrically conductive member disposed between cantilever beams  202 ,  204 . Air gap  214  is disposed between cantilever  204  and one end of the spark gap structure  200 , whereas air gap  216  is disposed between cantilever  202  and the other end of the spark gap structure  200 . The sum of gaps  214 ,  216  are typically between 0.030 and 0.060 inches. The gap structure  200  may be implemented such that the two gaps may be unequal. Further, one of the air gaps may be eliminated. Finally, an insulating material that bridges the gaps may be included. A typical length of the insulating material is at least 0.250 inches in length. 
         [0042]    As shown in  FIG. 1 , a second air gap structure  300  may be disposed between the load conductors  16 ,  18 . Referring to  FIG. 3 , a perspective view of the load spark gap structure  300  is disclosed. Spark gap structure  300  is disposed between conductors  16 ,  18  that connect the load terminals  24 ,  26  to fixed contacts  210 ,  212 . Spark gap structure  300  is also configured to absorb the energy generated by a severe voltage transient event. 
         [0043]    The present invention contemplates using any type of suitable structure to implement interrupting contacts  50 . Reference is made to U.S. patent application Ser. No. 10/900,769, filed Jul. 28, 2004, which is incorporated herein by reference as though fully set forth in its entirety, for a more detailed explanation of the various types of circuit interrupting structures that may be employed to implement the present invention. 
         [0044]      FIG. 4  is a partial sectional view of a device  10  that shows test circuit  400  and test button  402 . Contacts  404  are normally open. Using a GFCI as an example, test circuit  400  couples the hot load terminal  26  to neutral line terminal  20  when test button  402  is depressed (See also  FIG. 1  for a schematic representation). The resulting current through test circuit  400  is sensed by differential transformer  34  in the same manner as a true ground fault condition. The gap between open contacts  404  is required to be greater than a predetermined spacing to prevent the test circuit  400  from becoming damaged during a voltage transient event. The predetermined gap is approximately 0.100 inches. However, any requirement that would necessitate test button  402  to travel 0.100 inches to close the gap would not be ergonomic. Accordingly, the gap between test button  402  and contacts  404  may be reduced by providing gaps  406  and  408 . Note that the MOVs ( 56 ,  100 ) and the air gap structures ( 200 ,  300 ) provide the test circuit  400  with transient protection. 
         [0045]    In another embodiment, test circuit  400  may also be configured to provide automatic testing of device  10 . Reference is made to U.S. Pat. No. 6,674,289 and U.S. patent application Ser. No. 10/668,654 which are incorporated herein by reference as though fully set forth in its entirety, for a more detailed explanation of the automatic test circuit  400 . 
         [0046]    Referring to  FIG. 5 , a circuit diagram of a GFCI embodiment  10 ′ is shown. Device  10 ′ includes feed-through terminals  501  configured to connect device  10 ′ to the wiring that provides power to downstream receptacles. Device  10 ′ also includes receptacle load terminals  502  that are configured to accept a plug from a user attachable load. Interrupting contacts  505  are configured to disconnect the feed-through terminals  501  from the load terminals  502  when device  10 ′ is in the tripped condition. 
         [0047]    Indication components are included to alert the user to the reset or tripped status of device  10 ′. Indication components may include visual indicators, audible indicators, or both. Such indicators are configured to emit a steady indication or, alternatively, may emit an intermittent indication such as visual flashing or audible beeping. In particular, device  10 ′ provides an indicator  506  that is coupled in parallel with auxiliary switch  58 . Referring to the schematic diagram, indicator  506  emits a signal when device  10 ′ is connected to an AC power source and tripped. Indicator  508  may be coupled in series with auxiliary switch  58 . Indicator  508  emits a signal when device  10 ′ is connected to a source of power and is reset. Indicator  506  and indicator  508  may be used in combination or separately. Note that MOV  100  (or  56 ) limits the amplitude of the voltage transient that could otherwise create an end-of-life condition in the auxiliary switch  58 , or in the indicators  506 ,  508 . 
         [0048]    Referring to  FIG. 6 , a partial schematic diagram of a device in accordance with another embodiment of the present invention is shown. In this embodiment, MOV  600  is connected across the load terminals  24 ,  26 . MOV  600  is coupled to differential transformer  34  so as to generate a differential current when an end-of-life condition occurs. Transformer  34  is coupled to the load side of device  10 . In the manner previously described, the differential current is detected by detector  40 . In turn, detector  40  provides a signal to solid state switch  44  to energize solenoid  46 . Trip mechanism  48  is activated in response thereto, opening interrupting contacts  50 . Accordingly, an end-of-life condition in MOV  600  is interrupted before MOV  600  is able to overheat. The interruption of the current is accomplished by interrupting contacts  50 . MOV  56  and MOV  100  may be coupled to the line terminals  20 ,  22  by way of solenoid  46  in the manner previously described. 
         [0049]    All references, including publications, patent applications, and patents, cited herein are hereby incorporated by reference to the same extent as if each reference were individually and specifically indicated to be incorporated by reference and were set forth in its entirety herein. 
         [0050]    The use of the terms “a” and “an” and “the” and similar referents in the context of describing the invention (especially in the context of the following claims) are to be construed to cover both the singular and the plural, unless otherwise indicated herein or clearly contradicted by context. The terms “comprising,” “having,” “including,” and “containing” are to be construed as open-ended terms (i.e., meaning “including, but not limited to,”) unless otherwise noted. The term “connected” is to be construed as partly or wholly contained within, attached to, or joined together, even if there is something intervening. 
         [0051]    The recitation of ranges of values herein are merely intended to serve as a shorthand method of referring individually to each separate value falling within the range, unless otherwise indicated herein, and each separate value is incorporated into the specification as if it were individually recited herein. 
         [0052]    All methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. The use of any and all examples, or exemplary language (e.g., “such as”) provided herein, is intended merely to better illuminate embodiments of the invention and does not impose a limitation on the scope of the invention unless otherwise claimed. 
         [0053]    No language in the specification should be construed as indicating any non-claimed element as essential to the practice of the invention. 
         [0054]    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. There is no intention to limit the invention to the specific form or forms disclosed, but on the contrary, the intention is to cover all modifications, alternative constructions, and equivalents falling within the spirit and scope of the invention, as defined in the appended claims. 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.