Patent Publication Number: US-8120882-B1

Title: Protective electrical wiring device with light

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This is a continuation of U.S. patent application Ser. No. 10/998,369 filed on Nov. 29, 2004, 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. U.S. patent application Ser. No. 10/998,369 claims the benefit of priority under 35 U.S.C. §119(e) to U.S. provisional application Ser. No. 60/550,275 filed on Mar. 5, 2004, which is incorporated herein by reference in its entirety. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates generally to electrical wiring devices, and particularly to electrical wiring devices including protective circuitry. 
     2. Technical Background 
     Electrical wiring devices often include power receptacles that may receive a corded plug to thereby supply power to electrical equipment connected to the plug. In certain environments where a greater potential for an electrical shock hazard may exist, such as in a residential bathroom or kitchen, for example, the wiring device may be equipped with a circuit protection device component, e.g., a ground fault circuit interrupter (GFCI) (however, the use of wiring devices having a circuit protection device component or capability is in no way limited to these exemplary environments). Their intended purpose is to protect the electrical power user from electrocution when hazardous ground fault faults are present. Protective devices or device components may be effective in detecting ground faults associated with damaged insulation on the line conductor that could lead to fire, or to current accidentally flowing through a human body that could cause electrocution. In general, a GFCI senses and/or responds to a condition in a line carrying electrical current, which indicates a presently or imminently dangerous condition such as the presence of a current path other than the intended path of normal operation. Response to the sensed dangerous condition maybe in the form of alarm actuation and/or opening the line (interrupting the circuit) between the source of power and the load. 
     Protective device components are typically provided with line terminals for coupling to the supply voltage of the electrical distribution system, and load terminals coupled to the protected portion of the system and a circuit interrupter for disconnection of the load terminals from the line terminals. The protective device may be provided with a sensor for sensing the fault, a detector for establishing if the sensed signal represents a true hazardous fault, as opposed to electrical noise, and a switch responsive to the detector sensor, wherein the circuit interrupter comprising the contacts of a relay or trip mechanism are operated by a solenoid responsive to the switch to disconnect the load terminals from the line terminals. The disconnection is also known as tripping. A power supply may be required to furnish power to the sensor, detector, switch or solenoid. 
     Protective device components are commonly equipped with a test button, which the owner of the protective device is instructed to operate periodically to determine the operating condition of the sensor, the detector, the switch, trip mechanism or relay, or power supply, any of which can fail and which may cause the circuit interrupter to not operate to remove power from the load side of the protective device to interrupt the fault. Since the protective device component includes both electronic and mechanical components, failure modes may result from normal aging of electronic components, corrosion of mechanical parts, poor connections, mechanical wear, mechanical or overload abuse of the protective device in the field, electrical disturbances such as from lightning, or the like. Once the test has been manually initiated by operating the test button, the outcome of the test has often been indicated mechanically such as by a popping out of a button, visually through a lamp display or pivoting flag that comes into view, or audibly through an annunciator. As an alternative to a manual test, a self-test feature can be added to the protective device for automatic testing such as is described in U.S. Pat. No. 6,421,214 and U.S. application Ser. No. 09/827,007 filed Apr. 5, 2001 entitled LOCKOUT MECHANISM FOR USE WITH GROUND AND ARC FAULT CIRCUIT INTERRUPTERS, both of which are incorporated herein by reference in their entirety. Once the test has been automatically initiated through the self-test feature, the outcome of the test can be indicated by any of the previously described methods or by the permanent disconnection of the load terminals from the line terminals of the protective device component, also known as lock-out.” 
     Further variations on circuit protection device components exist. For example, commonly assigned copending application Ser. No. 10/768,530, filed on Jan. 30, 2004, entitled CIRCUIT PROTECTION DEVICE WITH GROUNDED NEUTRAL HALF CYCLE SELF TEST teaches a circuit protection device that self-checks for ground fault detection every half cycle. Commonly assigned copending application Ser. No. 10/729,392, entitled PROTECTION DEVICE WITH LOCKOUT TEST teaches a device that protects from arc faults and ground faults, which is provided with a manual test feature that permanently denies power to the protected circuit should the test fail. Commonly assigned U.S. Pat. No. 6,522,510 and U.S. application Ser. No. 09/718,003 filed Nov. 21, 2000, entitled GROUND FAULT CIRCUIT INTERRUPTER WITH MISWIRE PROTECTION AND INDICATOR teaches a ground fault interrupter device with miswire protection and indicator functions. These three applications are hereby incorporated by reference in there entireties to the fullest extent allowed by applicable laws and rules. 
     The exemplary bathroom and kitchen environments referred to above also represent locations that occupants may visit during night time hours when these rooms are typically dark. As such, it is common to find a “night light” plugged into an electrical receptacle to provide some increased visibility in the darkness. Night light devices have various forms, styles, and designs. They all include either an on/off switch for manual operation, or a sensor that senses ambient light conditions to control the on/off state of the light. An example of a night light having a sensor is disclosed in U.S. Pat. No. 6,561,677, which is herein incorporated by reference in its entirety. 
     In view of the foregoing information, the applicant has become appreciative of the various economies and other advantages and benefits presented by an electrical wiring device including a circuit protection component and an auxiliary, integrated light that provides lighting and/or circuit status indication. 
     SUMMARY OF THE INVENTION 
     The present invention addresses the needs described above by providing an electrical wiring device including a circuit protection component and an auxiliary, integrated light that provides lighting and/or circuit status indication. 
     One aspect of the present invention is directed to an electrical wiring device that includes a housing portion that has a plurality of line terminals and a plurality of load terminals accessible from external portions thereof. The housing portion further includes a separator member, the plurality of line terminals being disposed on a first side portion of the separator member, the plurality of load terminals also including a plurality of receptacle terminals disposed on a second side portion of the separator member. A cover portion is coupled to the housing portion. The cover portion includes a plurality of receptacle openings selectively coupled to the plurality of line terminals in an operative state. The cover portion also includes a user-accessible device control region disposed proximate the plurality of receptacle openings. The cover portion further includes at least one lens cover opening. A portion of the at least one first lens cover opening having a first edge juxtaposed with the user-accessible device control region and a second edge substantially disposed along a peripheral edge of the cover portion. An interrupting contact assembly includes four sets of interrupting contacts that are configured to provide electrical continuity between the plurality of line terminals and the plurality of load terminals in a reset state and configured to interrupt the electrical continuity in a tripped state. At least one detection circuit is disposed in the housing portion on the first side portion of the separator member and coupled to the plurality of line terminals or the plurality of load terminals. The at least one detection circuit is configured such that the interrupting contact assembly is substantially prevented from effecting the reset state in the event of a miswired condition, an end-of-life condition, or a fault condition. An illumination assembly is coupled to the at least one detection circuit and disposed in the housing portion. The illumination assembly includes at least one light emitting element, an illumination circuit, and at least one lens disposed in the at least one lens cover opening in optical communication with the at least one light emitting element. The illumination circuit is configured to selectively drive the at least one light emitting element between a deenergized state and a light emitting state in response to an ambient light condition, the miswire condition, the end-of-life condition, the reset state or the trip state. The at least one lens having a surface area that is a function of the first edge juxtaposed with the user-accessible device control region and the second edge substantially disposed along a peripheral edge of the cover portion such that light emitted by the at least one light emitting element is directed into a spatial volume proximate the electrical wiring device. 
     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 perspective line drawing of an electrical device according to an exemplary embodiment of the invention; 
         FIG. 2  is a perspective line drawing of the interior of the electrical device illustrated in  FIG. 1 ; 
         FIG. 3  is a perspective drawing of the interior of an electrical device according to another exemplary embodiment of the invention; 
         FIG. 4  is a perspective line drawing of the electrical device assembly illustrated in  FIG. 3 ; 
         FIG. 5  is a perspective line drawing of an electrical device according to another exemplary embodiment of the invention; 
         FIG. 6  is a perspective line drawing of an electrical device according to another exemplary embodiment of the invention; 
         FIG. 7  shows a circuit diagram for an exemplary ground fault circuit interrupter (GFCI); 
         FIG. 8  shows a partial sectional view of a mechanical implementation of the schematic of  FIG. 7 ; 
         FIG. 9  shows the mechanical implementation of  FIG. 8  in a tripped state; 
         FIG. 10  shows a partial sectional view of a mechanical implementation of an exemplary circuit protection component; 
         FIG. 11  shows a partial sectional view of the mechanical implementation of the present invention; 
         FIG. 12  shows a three-dimensional view of some of the components of the exemplary component of  FIG. 10 ; 
         FIG. 13  is a schematic circuit diagram of another exemplary protective device; 
         FIG. 14  is a schematic circuit diagram of another exemplary protective device; 
         FIG. 15  is a schematic circuit diagram of another exemplary protective device; 
         FIG. 16  is a schematic circuit diagram of another exemplary protective device; 
         FIG. 17  is a schematic circuit diagram of another exemplary protective device; 
         FIG. 18  is a schematic circuit diagram of another exemplary protective device; 
         FIG. 19  is a schematic circuit diagram of another exemplary protective device; 
         FIG. 20  is a block diagram of another exemplary circuit protection device; 
         FIG. 21  is a circuit schematic of the diagram depicted in  FIG. 20 ; 
         FIG. 22  is another circuit schematic of the diagram depicted in  FIG. 20 ; 
         FIGS. 23   a - 23   g  include timing diagrams illustrating the operation of the circuits depicted in  FIG. 21  and  FIG. 22 ; and 
         FIG. 24  is a schematic circuit diagram of another exemplary protective device. 
     
    
    
     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 electrical wiring device of the present invention is shown in  FIG. 1 , and is designated generally throughout by reference numeral  10 . 
     An embodiment according to the invention is now described with initial reference to  FIGS. 1 and 2 .  FIG. 1  shows an assembled perspective illustration of an exemplary electrical wiring device  100 - 1  having grounded receptacle openings  102 . The electrical wiring device  100 - 1  includes a housing  104  having a face portion  104   a , a back portion  104   b , and a separator portion  104   c  disposed therebetween. Receptacle openings  102  are formed in the face/cover portion  104   a . Line terminals  124  are disposed in the back portion  104   b  of the housing  104  underneath the bottom side of the separator member  104   c . Device  100 - 1  also includes load terminals  122 . The load terminals  122  are formed such that receptacle terminals  122   b  are disposed over the upper side of the separator member  104   c  and in spatial alignment with receptacle openings  102 . The device  100 - 1  also includes a circuit protection component  106  (described in greater detail below) contained within the housing, and a light source  108 , as shown in  FIG. 2 , contained within the housing. The light source  108  is covered by a lens cover  110  illustrated in  FIG. 1  and is therefore, disposed within the cover portion  104   a  above the upper side of separator  104   c . In an aspect of the embodiment, the light source  108  can provide an increased illumination in an environment surrounding the electrical wiring device. In this aspect, the light source would be coupled to the line terminals  124  ( FIG. 2 ), such that the light source is in an “on” state continuously as long as line power is being supplied to the device. In another aspect, the light source could function to provide an increased illumination in an environment surrounding the electrical wiring device in response to a predetermined condition. In this aspect, the light source would be coupled to the device so as to be in an “on” state continuously as long as line power is being supplied to the device, and the circuit protection component is in a “tripped” state due to a predetermined condition. 
     The light source  108  in all of the disclosed embodiments may be an LED. In alternative aspects, the light source may be a neon source, an incandescent source, or any other suitable source of illumination as a person skilled in the art will appreciate. The light source may be a single-unit source or a multi-unit source as shown, for example, as twin LEDs  108  in  FIG. 2 . The wavelength of the illumination produced by the light source will depend upon the type of source used, and can be selected as appropriate to the function being performed by the light source; e.g., a night-light, a status indicator, a room illuminator, etc. In another aspect of the embodiment, the light source may include terminals or wire leads that the installer connects to other terminals of the device. 
     In all of the disclosed embodiments, the lens cover  110  may be made of a clear or translucent material as a skilled person will appreciate as being best suited to factors such as the type of light source, the wavelength radiated by the light source, the desired intensity, or softness, of the illumination, the function of the light, and other considerations. In an aspect, the lens cover  110  is removable from the housing  104   a  for access to the light source  108 . In another aspect of all of the disclosed embodiments, the lens cover  110  has a height dimension, H, of not less than about 0.4 inch and a width, W, that substantially equals the width of the face portion of the housing  104   a  as shown, for example, in  FIGS. 1 ,  4 ,  5  and  6 . 
     Additional embodiments of the invention will now be set forth, and thereafter exemplary circuit protection components  106 - n  and associated circuits will be presented. It is to be appreciated that the design per se of the circuit protection component is not meant to limit the embodied invention in any way. Thus various circuit protection components in the form of ground fault circuit interrupters (GFCIs) and arc fault circuit interrupters (AFCIs), for example, as known in the art, as may be disclosed herein, or as described in commonly assigned copending applications incorporated herein by reference, will be suitable as persons skilled in the art will appreciate. 
     In another embodiment illustrated in  FIGS. 3 and 4 , an electrical wiring device  100 - 2  has all of the features described with reference to device  100 - 1  shown in  FIGS. 1 and 2 , and in addition includes a light source sensor  302  mounted within the housing and operably connected to the light source  108  for controlling an on/off state of the light source dependent upon an ambient light condition in the environment of the electrical wiring device. A lead  304  of light source  108  may be connected to receptacle  102 . Such electrical connection may be accomplished by way of crimping, soldering, welding or press-fitting, and the like. As shown in  FIG. 4 , a light source sensor lens cover  310  covers the light source sensor  302 . In an aspect, the light source sensor and light source sensor lens cover are located outside of a region occupied by the lens cover  110 . One exemplary advantage of such placement is the shielding of the sensor from light pollution produced by the light source  108 . In an aspect of the embodiment, light source sensor lens cover  310  extends around a portion of a side  104  as of the face portion  104   a  of the housing as illustrated in  FIG. 4 . In an alternative aspect, a wall-structure or other physical barrier prevents light contamination. 
     Another embodiment of the invention as illustrated in  FIG. 5  is directed to an electrical wiring device  100 - 3  having, in one aspect, all of the features described with reference to device  100 - 1  shown in  FIGS. 1 and 2 , and in addition includes a trip indicator  502  mounted in and visible through the housing  104   a  for indicating the status of the circuit protection component. In an alternative aspect illustrated in  FIG. 6 , the electrical wiring device  100 - 3 ′ has all of the features described with reference to device  100 - 2  shown in  FIGS. 3 and 4 , and in addition includes a trip indicator  502  mounted in and visible through the housing  104   a  for indicating the status of the circuit protection component. The trip indicator  502 , described in greater detail below with respect to the circuit protection component, can be a trip-light source, such as an LED, a neon source, or other suitable light source. A person skilled in the art will appreciate that different wiring permutations are possible for creating ON and OFF state combinations between the light source  108  and the trip indicator light source  502 . The trip light source  502  may emit a similar or a different color of light as the light source  108 , vary in intensity, or otherwise have characteristics in common, or not, with the light source  108 . In an aspect, the trip light source may be on continuously in an ON state or may blink in an ON state. In alternative aspects, the trip indicator need not be a light source, but rather could be an audible signal or indicator flag, as examples, as further described below. 
     Circuit Protection Device Components 
     An electrical distribution system typically includes a circuit breaker, branch circuit conductors, wiring devices, cord sets or extension cords, and electrical conductors within an appliance. A protective device typically is incorporated in an electrical distribution system for protecting a portion of the system from electrical faults. GFCIs are one type of protective device that provide a very useful function of disconnecting an electrical power source from the protected portion of the system when a ground fault is detected. Among the more common types of ground faults sensed by known GFCIs are those caused when a person accidentally makes contact with a hot electrical lead and ground. In the absence of a GFCI, life-threatening amounts of current could flow through the body of the person. 
     AFCIs are another type of protective device. AFCIs disconnect an electrical power source from a load when an arc fault is detected. Among the more common type of arc faults sensed by known AFCIs are those caused by damaged insulation such as from an overdriven staple. This type of arc fault occurs across two conductors in the electrical distribution system such as between the line and neutral conductors or line and ground conductors. The current through this type of fault is not limited by the impedance of the appliance, otherwise known as a load coupled to the electrical distribution system, but rather by the available current from the source voltage established by the impedance of the conductors and terminals between the source of line voltage and the position of the fault, thus effectively across the line, and has been known as a “parallel arc fault.” Another type of arc fault sensed by known AFCIs are those caused by a break in the line or neutral conductors of the electrical distribution system, or at a loose terminal at a wiring device within the system. The current through this type of fault is limited by the impedance of the load. Since the fault is in series with the load, this type of fault has also been known as a “series arc fault.” In the absence of an AFCI, the sputtering currents associated with an arc fault, whether of the parallel, series, or some other type, could heat nearby combustibles and result in fire. 
     Protective devices are typically provided with line terminals for coupling to the supply voltage of the electrical distribution system, and load terminals coupled to the protected portion of the system and a circuit interrupter for disconnection of the load terminals from the line terminals. The protective device is provided with a sensor for sensing the fault, a detector for establishing if the sensed signal represents a true hazardous fault, as opposed to electrical noise, and a switch responsive to the detector sensor, wherein the circuit interrupter comprising the contacts of a relay or trip mechanism are operated by a solenoid responsive to the switch to disconnect the load terminals from the line terminals. The disconnection is also known as “tripping”. A power supply may be required to furnish power to the sensor, detector, switch or solenoid. 
     In one approach, a protective device is equipped with a test button, which the owner of the protective device is instructed to operate periodically to determine the operating condition of the sensor, the detector, the switch, trip mechanism or relay, or power supply. Any of these components may fail and cause the circuit interrupter to fail to remove power from the load side of the protective device to interrupt the fault. Since the protective device comprises electronic and mechanical components, failure may occur because of normal aging of the electronic components, corrosion of the mechanical parts, poor connections, mechanical wear, mechanical or overload abuse of the protective device in the field, electrical disturbances (e.g., lightning), or for other reasons. Once the test has been manually initiated by operating the test button, the outcome of the test may be indicated mechanically by a button, or visually through a lamp display or pivoting flag that comes into view, or audibly through an annunciator. 
     In another approach, a self-test feature can be added to the protective device for automatic testing as an alternative to a manual test. Once the test has been automatically initiated through the self-test feature, the outcome of the test can be indicated by any of the previously described methods or by the permanent disconnection of the load terminals from the line terminals of the protective device, also known as “lock-out.” 
     Another approach that has been considered is depicted in  FIG. 7 . GFCI  2  includes line terminals  3  and  5  for coupling to a power source of the electrical distribution system and load terminals  37  and  39  appropriate to the installed location, whether a circuit breaker, receptacle, plug, module, or the like. A ground fault represented by resistor  41  produces an additional current in conductor  4  that is not present in conductor  6 . Sensor  12  senses the difference current between conductors  4  and  6 , which is then detected by a ground fault detector  14 . Detector  14  issues a trip command to a silicon controlled rectifier  22  (SCR) that in turn activates a solenoid  24 , which activates a trip mechanism  26  releasing contact armatures  34  and  32 , thereby disconnecting power to the load by breaking the circuit from a line hot  4  to a load hot  36  and from a line neutral  6  to a load neutral  38 . A contact  10  along with a resistor  8  form a test circuit that introduces a simulated ground fault. When contact  10  is depressed, the additional current on conductor  4  is sensed by sensor  12  as a difference current causing the device to trip. Current flows through resistor  8  for the interval between depression of the contact  10  and the release of contact armatures  34  and  32 , which is nominally 25 milliseconds. The device is reset by pressing a reset button  40 , which mechanically resets trip mechanism  26 . A resistor  20 , a Zener  18 , and a capacitor  19  form a power supply for GFCI  2 . 
     Referring to  FIG. 8 , the mechanical layout for the circuit diagram of  FIG. 7  is shown in which like elements are like numbered. Trip mechanism  26  is shown in the set state, meaning that contacts  37  and  35  are closed. Contacts  35  and  37  are held closed by action of a trapped make-force spring  46  acting on an escapement  55  on a rest stem  54  to lift a reset latch spring  52  and by interference, an armature  32 . Reset latch spring  52  includes a hole  53  and armature  32  includes a hole  33 , which holes  33  and  53  permit entry of a tip  58  of reset stem  54 . Reset stem  54  is held in place by a block  60 . Armature  32  and a printed circuit board (PCB)  56  are mechanically referenced to a housing  48  so that the force in spring  46  is concentrated into armature  32 . 
     Referring to  FIG. 9 , the mechanism of  FIG. 8  is shown in the tripped state. The tripped state occurs when SCR  22  activates a magnetic field in solenoid  24 , which in turn pulls in plunger  23  to displace reset latch spring  52 . Displacing reset latch spring  52  allows a flat portion  55  to clear the latch spring  53  interference, which then releases the interference between latch spring  52  and armature  32 . Armature  32  has a memory that returns armature  32  to a resting position against solenoid  24 , opening contacts  35  and  37  and disconnecting power to the load. 
     An exemplary embodiment of another GFCI is shown in  FIGS. 10-19  and is designated herein by reference numeral  2 . 
     Referring to  FIG. 10 , a partial sectional view of a mechanical implementation of an embodiment of the invention is shown. A resistor  8 ′, shown schematically in  FIG. 7  as resistor  8 , is designed to withstand self-heating that results from each depression of contact  10 , which causes current to flow through resistor  8 ′ for the expected trip time of the GFCI. For example, resistor  8 ′ for a 6 mA GFCI coupled to a 120V AC supply is required by UL to be 15 KOhms, which dissipates nominally 0.96 W during each trip time interval. In particular, resistor  8 ′ must survive several thousand trip time intervals accomplished by depressing contact  10  and reset button  40  alternately. During normal operation of GFCI  2 , resistor  8 ′ is physically positioned to restrain lockout spring  400 . Resistor  8 ′ is preferably mounted and soldered so that the body of resistor  8 ′ impedes movement of lockout spring  400 . 
     Referring to  FIG. 11 , a partial sectional view of the mechanical implementation of  FIG. 10  is shown in the lock-out position. The GFCI  2  has failed in some manner such that the trip time in response to depressing contact  10  is greater than the expected interval including failure of GFCI  2  to trip altogether. Examples of failure modes include a defective sensor  12 , and for a sensor  12  comprising a transformer, open or shorted turns. The detector  14 , typically composed of electronic components, may have poor solder connections or components that have reached end of life. The SCR  22  may short circuit either due to reaching end of life or due to a voltage surge from a lightning storm, thereby causing continuous current through solenoid  24  which burns open through over activation, or, alternatively, SCR  22  may open circuit. The mechanical components associated with trip mechanism  26  may become immobilized from wear or corrosion. The power supply, if provided, may fail to deliver power in accordance with the design such that sensor  12 , detector  14 , SCR  22 , or solenoid  24  are non-operative. 
     When failure of GFCI  2  occurs, the current through resistor  8 ′ flows for the time that contact  10  is manually depressed, on the order of at least seconds, which is two orders of magnitude longer than if the trip mechanism  26  were to operate in response to depressing contact  10 . Resistor  8 ′, which is preferably coupled electrically to GFCI  2  through solder, heats from the current and melts the solder. Resistor  8 ′, no longer restrained by the solder, or in an alternative embodiment by an adhesive, is physically dislodged by the bias of lockout spring  400 . Force is then applied by an end  404  of lock-out spring  400  against a feature on the reset latch spring  52 , for example, a tab  402 . The force in lockout spring  400  is greater than the force in reset latch spring  52 . As previously described, reset latch spring  52  is displaced allowing a flat portion  55  to clear the latch spring  53  interference, which then releases the interference between reset latch spring  52  and armature  32 . Armature  32  has a memory that returns armature  32  to a resting position against solenoid  24 , opening contacts  35  and  37  and disconnecting power to the load. Thus when the GFCI  2  is operational, the tripping mechanism  26  is able to operate, and the armatures  32  and  34  disconnect when plunger  23  applies force to reset latch spring  52 . If GFCI  2  is not operative, lockout spring  400  applies force to reset latch spring  52 , likewise causing armatures  32  and  34  to disconnect. When GFCI  2  is tripped under the influence of lockout spring  400 , armatures  32  and  34  are permanently disconnected irrespective of depressing contact  10  or reset button  40  or any further movement in plunger  23 . 
     Referring to  FIG. 12 , components of the embodiment of  FIG. 10  are shown in a three-dimensional view including lockout spring  400 , end  404 , resistor  8 ′, and latch spring  52 . Spring  404  is preferably affixed to the same structure as resistor  8 ′. 
     Referring to  FIG. 13 , a protective device  71   0  shows a resistor  700 , which is then used as the resistor body that constrains spring  400 . There are other ground fault circuit interrupters whose trip thresholds are greater than 6 mA, intended for a variety of supply voltages or phase configurations, and intended for personal protection or fire prevention. Alternative trip levels typically include 30 mA in the US. or Europe, or 300 or 500 mA in Europe. For devices where the current through resistor  8  may produce insufficient heat during the anticipated duration that contact  10  is manually depressed to melt the solder, resistor  8  can be supplemented by a resistor  700  in parallel with resistor  8 , which connects to line  6  on the other side of sensor  12  [Tom where resistor  8  connects to line  6 . Currents through resistors  8  and  700  are enabled by depressing contact  10 . Resistor  8  generates a simulated test signal comprising a difference current to test GFCI  2  as previously described. Resistor  700  is coupled so as to conduct common mode current but no difference current. Since the current through resistor  700  does not influence the amount of simulated test current required by UL, which is set by the value of resistor  8 , the value of resistor  700  can be whatever value is convenient for producing sufficient heat in resistor  700  when contact  10  is manually depressed to release lockout spring  400  when GFCI  2  is not operational.  FIG. 13  also shows how the lockout function is unaffected by whether the power supply for the GFCI comprising resistor  20 , Zener  18 , and capacitor  19  are coupled to the load side of armatures  32  and  34 . Load side power derivation may be convenient for GFCIs or protective devices housed in a circuit breaker.  FIG. 13  also shows how SCR  22  can be replaced by a transistor  22 ′, with either device comprising a switch for controlling solenoid  24 . 
     Referring to  FIG. 14 , a protective device  810  that is an alternate embodiment to  FIG. 13 , shows a resistor  800  that serves the same function as resistor  700  in  FIG. 13  but is coupled to the load side of the interrupting contacts, i.e., contact armatures  32 ,  34 . This may be important for 6 mA GFCI receptacles and portables where the hot and neutral supply conductors are inadvertently transposed by the installer, wherein the hot side of the supply voltage from the electrical distribution system is connected to line terminal  5 . If the armatures  32  and  34  in  FIG. 13  are disconnected in response to a fault current, a hazardous current may yet flow through resistors  8  and  700  through ground fault  702  when contact  10  is depressed. However, if armatures  32  and  34  in  FIG. 14  are disconnected, current flows through resistor  8  but not through resistor  800 , which is not a problem because the current flow through resistor  8  alone has already been determined to be non-hazardous. 
     Referring to  FIG. 15 , a protective device  910 , which is an alternative embodiment to  FIG. 14 , is shown in which the trip mechanism comprises one or more bus bars. Reference is made to U.S. Pat. No. 5,510,760, which is incorporated herein by reference as though fully set forth in its entirety, for a more detailed explanation of the bus bar arrangement. Resistor  900  serves the same function as resistor  800  in  FIG. 14  except that resistor  900  is coupled to moveable bus bar  902 ′. For receptacle housings it is possible for the installer to miswire a GFCI such that the supply voltage is connected to load terminals  37  and  39 , which would cause resistor  800  ( FIG. 14 ) to melt solder when contact  10  is depressed, even when device  810  is in good working condition, i.e., operational. The problem is alleviated in the embodiment of  FIG. 15  whereby resistor  900  melts solder only when bus bar  902 ′ remains connected when contact  10  is depressed, that is, when device  910  is non-operational. Miswiring thus does not cause a permanent lock-out of device  910 . 
     Referring to  FIG. 16 , a protective device  1010  which is an alternate embodiment to  FIG. 13  is shown, wherein contact  10  enables a current through resistor  8 , as previously described, and a second current through a resistor  1000  in which the second current is preferably less than a tenth of the current through resistor  8 . The second current depends on an interface circuit such as a transistor switch  1002 . Transistor switch  1002  causes current to flow through a resistor  1004  of identical function to resistor  700  described in  FIG. 13 , i.e., resistor  1004  is normally in such a position as to leave spring  400  ( FIG. 12 ) under tension, but when resistor  1004  heats up from the current through it sufficient to dislodge the solder affixing resistor  1004  to a fixed reference surface, the dislodgement of resistor  1004  releases spring  400 . 
       FIG. 16  shows an alternative to  FIG. 14  wherein a hazardous current does not occur when the hot and neutral supply conductors are inadvertently transposed as described in  FIG. 14 . In addition,  FIG. 16  shows another remedy for the issue described in the  FIG. 15  embodiment wherein resistor  1004  melts solder only if protective device  1010  is non-operational and not when protective device  1010  is miswired. 
     Referring to  FIG. 17 , a protective device such as GFCI  1110  according to an alternate embodiment is shown, wherein the so called mouse trap mechanism, i.e., the tripping mechanism of the GFCI of  FIGS. 7-11 , is replaced by a relay  1100  having normally open contacts  1102  that connect or disconnect line terminals  3  and  5  from load terminals  37  and  39  respectively, and a solenoid  1104 , which is designed to carry current when contacts  1102  of GFCI  1110  are connected, a construction that is common to, but not limited to, portable GFCI devices. Solenoid  1104  is designed to conduct current for the unlimited duration that GFCI  1110  is in use, wherein solenoid  1104  is not susceptible to burn out caused by over-activation as previously described with respect to solenoid  24 . A fusible element  1106  is in series with the solenoid and is designed to carry the continuous current through solenoid  1104  when transistor  22 ′ is closed. Contact  10  enables current through resistor  8 , which produces a difference current as previously described, and a common mode current, which, if the device is non-operational, enables a lock-out feature. The common mode current, which is greater than the solenoid current, is conducted through fusible element  1106 . 
     If GFCI  1110  is operational, the load side is disconnected from the line side, causing the device to trip and resistor  8  and common mode currents to stop flowing even if contact  10  continues to be manually depressed. Fusible resistor  1106  must survive several thousand cycles of common mode current exposures from alternately depressing contact  10  to trip GFCI  1110  and switch  1108  to electronically reset GFCI  1110 . The duration of each common mode current exposure is the expected time that GFCI  1110  requires for tripping after contact  10  has been depressed. If GFCI  1110  fails in some manner such that the trip time in response to depressing contact  10  is greater than the expected interval including the failure of GFCI  1110  to trip altogether, fusible element  1106  burns to an open circuit, permanently eliminating current through solenoid  1104  and rendering interrupting contacts  1102  in a permanently disconnected position. Fusible element  1106  can include a resistor. 
     Referring to  FIG. 18 , elements of the circuit diagram of  FIG. 17  are combined with elements of the circuit diagram of  FIG. 14  in a protective device  1210 , wherein components having like functions bear like numbers. The concept shown in  FIG. 17  is thus combined with the embodiment of  FIG. 14  to protect against the inadvertent transposing of the hot and neutral supply conductors to terminals  3  and  5  from the electrical distribution system. For protective devices not equipped with a resistor  8 , the value of resistor  1000  can be chosen so that current passing there through is less than 0.5 mA, which limit has been identified to be the perception level for humans. 
     Referring to  FIG. 19 , an alternate embodiment is shown in which the preceding concepts are applied to a general protective device  1310  representative of the class of general protective devices including AFCIs that require a contact  10  but that are not necessarily equipped with a GFCI or a sensor capable of sensing difference current. Reference is made to U.S. Pat. No. 6,421,214, which is incorporated herein by reference as though fully set forth in its entirety, for a more detailed explanation of protective device  1310 . Components having like functions bear like numbers. Sensor  1300  is similar to sensor  12  but may be a current sensor or shunt for sensing load current through either conductor  6  or through conductor  4 . A detector  1302  is similar to detector  14  ( FIG. 7 ) but senses particular signatures in the load current as has been demonstrated in other patent applications as a method of identifying arc faults. A contact  1304  is similar to contact  10  ( FIG. 7 ), which initiates a test of protective device  1310  when depressed. The test signal can be controlled by detector  1302  to test sensor  1300 , detector  1302 , switch  22 , and trip mechanism  26 . A resistor  1306  is similar to resistor  700  ( FIG. 13 ), which is affixed to a fixed reference surface. If armatures  32  and  34  fail to operate due to a malfunction of protective device  1310 , the longer duration of current through resistor  1306  causes sufficient self-heating of resistor  1306  to melt the solder affixing resistor  1306  to the fixed reference surface, wherein resistor  1306  is dislodged due to force exerted by lockout spring  400  ( FIG. 10 ), wherein lockout spring  400  causes armatures  32  and  34  to be permanently disconnected. 
     Another exemplary circuit protection component is shown in  FIG. 20 . The block diagram of  FIG. 20  is a GFCI  10  configured to introduce a simulated ground fault every period during the negative half cycle that the trip SCR cannot conduct. If the device fails to detect the simulated ground fault, i.e., the self-test fails, the device is tripped on the next positive half cycle. 
     As shown in  FIG. 20 , GFCI  10  protects an electrical circuit that provides electrical power to load  8 . GFCI  10  is connected to the AC power source by way of line-side neutral terminal  11  and line-side hot terminal  13 . GFCI  10  is coupled to load  8  by way of load side neutral terminal  12  and load-side hot terminal  14 . GFCI  10  includes two main parts, Ground Fault Interrupt (GFI) circuit  102  and checking circuit  100 . 
     GFI circuit  102  includes a differential sensor  2  that is configured to sense a load-side ground fault when there is a difference in Current between the hot and neutral conductors. Differential sensor  2  is connected to detector circuit  16 , which processes the output of differential sensor  2 . Detector  16  is connected to power supply circuit  18 . Power supply  18  provides power for allowing detector  16  to detect a ground fault during both the positive half-cycle and the negative half cycle of the AC power. As such, detector circuit  16  provides all output signal on output line  20 . The output line  20  is coupled to SCR  24  by way of filter circuit  22 . When detector circuit  16  senses a fault, the voltage signal on output line  20  changes and SCR  24  is turned ON. SCR  24  is only able to turn ON during the positive half cycles of the AC power signal. Further, snubber network  36  prevents SCR  24  from turning on due to spurious transient noise in the electrical circuit. When SCR  24  is turned ON, solenoid  38  is activated. Solenoid  38 , in turn, causes the trip mechanism  40  to release the interrupter contacts  42 . When interrupter contacts  42  are released, the load-side of GFCI  10  is decoupled from the line-side power source of the electrical circuit. GFI circuit  102  also includes a grounded neutral transmitter  3  that is configured to detect grounded neutral conditions. Those skilled in the art understand that the conductor connected to neutral terminal  11  is deliberately grounded in the electrical circuit. On the other hand, a grounded neutral condition occurs when a conductor connected to load neutral terminal  12  is accidentally grounded. The grounded neutral condition creates a parallel conductive path with the return path disposed between load terminal  12  and line terminal  11 . When a grounded neutral condition is not present, grounded neutral transmitter  3  is configured to couple equal signals into the hot and neutral conductors. As noted above, differential sensor  2  senses a current differential. Thus, the equal signals provided by grounded neutral transmitter  3  are ignored. However, when a grounded neutral condition is present, the signal coupled onto the neutral conductor circulates as a current around the parallel conductive path and the return path, forming a conductive loop. Since the circulating current conducts through the neutral conductor but not the hot conductor, a differential current is generated. Differential sensor  2  detects the differential current between the hot and neutral conductors. As such, detector  16  produces a signal on output  20  in response to the grounded neutral condition. 
     Interrupter contacts  42  are coupled to trip mechanism  40 . Interrupter contacts  42  are configured to selectively couple and decouple the load-side terminals ( 12 ,  14 ) from the corresponding line-side terminals ( 11 ,  13 ). In one embodiment, trip mechanism  40  is arranged in what is known in the art as a mouse trap arrangement. Interrupter contacts  42  include spring loaded contacts. When the trip mechanism  40  is activated, the spring-loaded contacts  42  are opened and latched in an open condition. Interrupter contacts  42  are manually reset (closed) by depressing reset button  44 . 
     In another embodiment, trip mechanism  40  and circuit interrupter  42  may be configured as a relay in which the contacts are normally open. In this alternative construction, when the trip mechanism  40  is de-activated, the contacts are biased open until such time as trip mechanism  40  is re-activated. As noted previously, GFCI  10  is configured to detect both ground faults and grounded neutral conditions. 
     As noted initially, GFCI  10  includes a checking circuit  100 . Checking circuit  100  causes GFI  102  to trip due an internal fault also known as an end of life condition. Examples of an end of life condition include, but are not limited to, a non-functional sensor  2 , grounded neutral transmitter  3 , ground fault detector  16 , filtering circuit  22 , SCR  24 , snubber  36 , solenoid  38 , or power supply  18 . An internal fault may include a shorting or opening of an electrical component, or an opening or shorting of electrical traces configured to electrically interconnect the components, or other such fault conditions wherein GFI  102  does not trip when a grounded neutral fault occurs. 
     Referring to  FIG. 20 , checking circuit  100  includes several functional groups. The components of each group are in parenthesis. These functions include a fault simulation function ( 92 , 94 , 96 ), a power supply function  78 , a test signal function ( 38 ,  80 ,  82 ,  84 ), a failure detection function ( 86 ), and failure response function ( 88 , 90 , 91 ). 
     Fault simulation is provided by polarity detector  92 , switch  94 , and test loop  96 . Polarity detector  92  is configured to detect the polarity of the AC power signal, and provide an output signal that closes switch  94  during the negative half cycle portions of the AC power signal, when SCR  24  cannot turn on. Test loop  96  is coupled to grounded neutral transmitter  3  and ground fault detector  2  when switch  94  is closed. Loop  96  has less than 2 Ohms of resistance. Because polarity detector  92  is only closed during the negative half cycle, electrical loop  96  provides a simulated grounded neutral condition only during the negative half cycle. However, the simulated grounded neutral condition causes detector  16  to generate a fault detect output signal on line  20 . 
     The test signal function provides an oscillating ringing signal that is generated when there is no internal fault condition. Capacitor  82  and solenoid  38  form a resonant circuit. Capacitor  82  is charged through a diode  80  connected to the AC power source of the electrical circuit. SCR  24  turns on momentarily to discharge capacitor  82  in series with solenoid  38 . Since the discharge event is during the negative half cycle, SCR  24  immediately turns off after capacitor  82  has been discharged. The magnitude of the discharge current and the duration of the discharge event are insufficient for actuating trip mechanism  40 , and thus interrupting contacts  42  remain closed. When SCR  24  discharges capacitor  40  during the negative AC power cycle, a field is built up around solenoid  38  which, when collapsing, causes a recharge of capacitor  82  in the opposite direction, thereby producing a negative voltage across the capacitor when referenced to circuit common. The transfer of energy between the solenoid  38  and capacitor  82  produces a test acceptance signal as a ringing oscillation. Winding  84  is magnetically coupled to solenoid  38  and serves as an isolation transformer. The test acceptance signal is magnetically coupled to winding  84  and is provided to reset delay timer  86 . 
     The failure detection function is provided by delay timer  86  and SCR  88 . Delay timer  86  receives power from power supply  78 . When no fault condition is present, delay timer  86  is reset by the test acceptance signal during each negative half cycle preventing timer  86  from timing out. If there is an internal fault in GFI  102 , as previously described, the output signal on line  20  and associated test acceptance signal from winding  84  which normally recurs on each negative half cycle ceases, allowing delay timer  86  to time out. 
     SCR  88  is turned on in response to a time out condition. SCR  88  activates solenoid  90 , which in turn operates the trip mechanism  40 . Subsequently, interrupter contacts  42  are released and the load-side terminals ( 12 ,  14 ) are decoupled from the power source  0  f the electrical circuit. If a user attempts to reset the interrupting contacts by manually depressing the reset button  44 , the absence of test acceptance signal causes GFI  10  to trip out again. The internal fault condition can cause GFI  10  to trip, and can also be indicated visually or audibly using indicator  91 . Alternatively, solenoid  90  can be omitted, such that the internal fault condition is indicated visually or audibly using indicator  91 , but does not cause GFI  10  to trip. Thus the response mechanism in accordance with the present invention can be a circuit interruption by circuit interrupter  40 , an indication by indicator  90 , or both in combination with each other. GFI  10  includes a light source  108 . GFI  10  may include an indicator  91  viewable through front housing  104   a  in a similar manner as trip indicator  502  as depicted in  FIG. 5 . Indicator  91  may be “on continuously” in an “on” state or may “blink” in an “on” state when GFI  10  (or protective device  1310 ) has reached an end of life condition. In particular, indicator  91  may be a blinking red indicator. The trip indicator need not be a light source, but rather could be an audible signal that emits a steady sound or a beeping sound, or could be an indicating flag. In another aspect, GFI  10  (or protective device  1310 ) includes a light source  108 , trip indicator  502 , and internal fault (end of life) indicator  91 . In another aspect, indicator  91  and trip indicator  502  are combined into a single visual indicator. In another aspect, indicator  91  and light source  108  are combined in a single visual indicator. For those aspects in which a single indicator is employed, the various types of indication are distinguished by different colors, blinking patterns, or the like. Checking circuit  100  is also susceptible to end of life failure conditions. Checking circuit  100  is configured such that those conditions either result in tripping of GFI  102 , including each time reset button  44  is depressed, or at least such that the failure does not interfere with the continuing ability of GFI  102  to sense, detect, and interrupt a true ground fault or grounded neutral condition. For example, if SCR  88  develops a short circuit, solenoid  90  is activated each time GFI  102  is reset and GFI  102  immediately trips out. If one or more of capacitor  82 , solenoid  90  or winding  84  malfunction, an acceptable test signal will not be generated, and checking circuit  100  will cause GFI  102  to trip out. If polarity detector  92  or switch  94  are shorted out, the grounded neutral simulation signal is enabled during both polarities of the AC power source. This will cause GFI  102  to trip out. If polarity detector  92  or switch  94  open circuit, there is absence of grounded neutral simulation signal, and delay timer  86  will not be reset and GFI  102  will trip out. Solenoids  38  and  90  are configured to operate trip mechanism  40  even if one or the other has failed due to an end of life condition. Therefore if solenoid  90  shorts out, trip mechanism  40  is still actuatable by solenoid  38  during a true fault condition. If power supply  78  shorts out, power supply  18  still remains operational, such that GFI  102  remains operative. 
     Although much less likely to occur, some double fault conditions cause GFI  102  to immediately trip out. By way of illustration, if SCR  88  and SCR  24  simultaneously short out, solenoids  38  and  90  are both turned on, resulting in activation of trip mechanism  40 . 
     In another embodiment, solenoid  90  can be omitted and SCR  88  reconnected as illustrated by dotted line  93 . During a true fault condition, solenoid  38  is turned on by SCR  24 . When an end of life condition in GFI  102  is detected by checking circuit  100 , solenoid  38  is turned on by SCR  88 . The possibility of a solenoid  38  failure is substantially minimized by connecting solenoid  38  to the load side of interrupting contacts  42 . 
     As has been described, wire loop  96  includes a portion of the neutral conductor. A segment of the hot conductor can be included in electrical loop  96  instead of the neutral conductor to produce a similar simulation signal (not shown.) Other modifications may be made as well. The neutral conductor (or hot) conductor portion has a resistance  98 , typically 1 to 10 milliohms, through which current through load  8  flows, producing a voltage drop. The voltage drop causes a current in electrical loop  96  to circulate which is sensed by differential sensor  2  as a ground fault. Consequently, ground fault detector  16  produces a signal on output  20  due to closure of test switch  94  irrespective of whether or not an internal fault has occurred in neutral transmitter  3 . In order to assure that grounded neutral transmitter  3  is tested for a fault by checking circuit  100 , electrical loop  96  can be configured as before but not to include a segment of the neutral (or hot) conductor, as illustrated by the wire segment, shown as dotted line  95 . 
     As depicted in  FIG. 21 , a circuit schematic of the diagram depicted in  FIG. 20  is shown. In  FIG. 21 , ground fault detector  16  is an RV 4141 integrated circuit manufactured by Fairchild Semiconductor. Ground fault detector  2  is implemented as a toroidally shaped magnetic core  200  about which a winding  202  is wound. Winding  202 , typically having 1,000 turns, is coupled to an input terminal  204  of ground fault detector  16 . Grounded neutral transmitter  3  is implemented as a second toroidally shaped magnetic core  206  about which a winding  208  is wound. Winding  208 , typically having 200 turns, is coupled in series with a capacitor  210  to the gain output terminal  212  of ground fault detector  16 . Hot and neutral conductors  13  and  11 , and wire segment  95  if used, pass through the apertures of cores  200  and  206 . 
     During either a true grounded neutral condition, or during a simulated grounded neutral condition, low level electrical noise indigenous to the electrical circuit or to ground fault detector  16  creates a magnetic flux in either core  200  or  206 , or both, flux in core  206  having been induced by winding  208 . Core  206  induces a circulating current in electrical loop  96 , which induces a flux in core  200 . The resulting signal from winding  202  is amplified by the gain of ground fault detector  16  to produce an even greater flux in core  206  via winding  208 . Through the regenerative feedback action as has been described, ground fault detector  16  breaks into oscillation, typically 5 to 10 kHz. The oscillation produces a signal on output  20  during a grounded neutral fault or simulated grounded condition as has been previously described. 
     As shown in  FIG. 21 , switch  94  may be implemented as an analog switch, such as USW 1 MAX 4626, manufactured by Maxim Semiconductor. Polarity detector  92  may be implemented using transistor  214 , which closes switch  94  during the negative half cycle portions of the AC power supply of the electrical distribution system. 
     Delay timer  86  includes a capacitor  216 , which is configured to hold a pre-established voltage when test acceptance signals are properly received. The pre-established voltage prevents transistor  218  from turning SCR  88  ON. An end of life condition is signaled by the cessation of the test acceptance signal. In the absence of the test acceptance signal, the voltage on capacitor  216  decays below the pre-established voltage within a pre-established time interval, the rate of decay being established by bleeder  220 . In response, transistor  218  actuates SCR  88  and GFI  102  is tripped. The pre-established time interval is chosen such that checking circuit  100  is not responsive to normal transient conditions that may exist in the electrical circuit, such as momentary or intermittent loss of AC power supply voltage or momentary voltage transients, but responsive solely to end of life conditions. 
     GFCI  10  may be equipped with a manually accessible test button  222  for closing switch contacts  224  for initiating a simulated grounded hot fault signal, or alternatively, a simulated grounded neutral fault signal. If GFI  10  is operational, closure of switch contacts  224  initiates a tripping action. The purpose of the test button feature may be to allow the user to control GFCI  10  as a switch for applying or removing power from load  8 , in which case test button  22  and reset button  44  have been labeled “off” and “on” respectively. Usage of test button  222  does not affect the performance of checking circuit  100 , or vice-versa. 
     GFCI  10  may also be equipped with a miswiring detection feature such as miswire network  46 . Reference is made to U.S. Pat. No. 6,522,510, which is incorporated herein by reference as though fully set forth in its entirety, for a more detailed explanation of miswire network  46 . Briefly stated, miswire network  46  is configured to produce a simulated ground fault condition. During the installation of GFCI  10  if the power source voltage is coupled to the line terminals  11  and  13  as intended, the current through network  46  causes GFI  102  to trip but the current through network  46  continues to flow, until such time as network  46  open circuits due to heating of a fusible component included in network  46 . The fusible component may be implemented by resistor  228 , configured to fuse in typically 1 to 10 seconds. When the fusible component opens, the GFCI is able to be reset. Subsequently, GFI  102  and checking circuit  100  operate in the previously described manner. However, if the power source is connected to the load terminals, i.e., if GFCI  10  is miswired during installation, GFI  102  trips as before, but interrupting contacts  42  immediately terminate the current flow through network  46 , typically in less than 0.1 seconds. This time period is too brief an interval to cause the fusible component to fail. Thus, when GFCI  10  is miswired the fusible element in network  46  remains intact, and reset button  44  cannot effect a resetting action. GFCI  10  cannot be reset regardless of signals to or from checking circuit  100 . 
     If GFCI  10  is properly wired and tested during an installation, miswire network  46  will fuse open and not be available to afford miswire protection if GFCI  10  happens to be re-installed. However, the checking circuit  100  can be configured to extend miswire protection to the re-installation. During the course of re-installation, the user depresses test button  222  to close contacts  224 . If GFCI  10  has been miswired, power supply  78  is connected to the load side of interrupting contacts  42  and delay timer  86  receives power. Power supply  18  is connected to a bus bar  230  between interrupting contacts  42  and  42 ′. Since interrupting contacts  42 ′ are open, ground fault detector  16  does not receive power, and test acceptance signal is not communicated by winding  84  to charge capacitor  216  to a voltage greater than the pre-determined threshold. As a result, transistor  218  turns SCR  88  ON, and solenoid  90  activates trip mechanism  40 . Whenever the reset button is depressed, the trip mechanism is activated such that the interrupter contacts do not remain closed. Thus, the checking circuit  100  interprets miswiring as it would an end-of-life condition. Thereafter, GFCI  10  can only be reset when it is re-installed and wired properly. 
     A circuit schematic of the diagram depicted in  FIG. 20  is shown in  FIG. 22 . Grounded neutral transmitter  3 ′ includes a saturating core  300  and a winding  302  coupled to hot and neutral terminals  13  and  11 . During a true grounded neutral fault condition, saturating core  300  induces current spikes in the electrical loop  96 . Reversals in the magnetic field in core  300  correspond to the zero crossings in the AC power source. The reversals in the magnetic field generate current spikes. Current spikes occurring during the positive-transitioning zero crosses produce a signal during the positive half cycle portions of the AC power source. The signal is sensed as a differential signal by ground fault sensor  2 , and detected by ground fault detector  16 . Subsequently, GFI  102  is tripped. A simulated grounded neutral condition is enabled by polarity detector  92  and switch  94 . Polarity detector  92  closes switch  94  during the negative half cycle. Thus, the current spikes occur during the negative half cycle portions but not during the positive half cycle portions of the AC power source. As described above, the output of detector  16  (line  20 ) during the negative half cycle portions of the AC power source are unable to turn on SCR  24 . However, the output signal is used by checking circuit  100  to determine whether or not an end of life condition has occurred. 
     In yet another embodiment (not shown), the grounded neutral transmitter winding  208  can be connected to a local oscillator that provides a continuous oscillatory output signal regardless of the presence or absence of electrical loop  96 . 
     The frequency from the oscillator is typically 5 to 10 kHz. The oscillator induces a flux in core  206  via winding  208 . The true grounded neutral fault couples the flux in core  206  into differential sensor  2 , causing GFI  102  to trip as described above. The simulated grounded neutral condition, enabled by closure of switch  94  during the negative half cycle portions of the AC power source, provides for an end of life test signal, whose absence is interpreted by checking circuit  100  as an end of life condition. 
     It will be apparent to those of ordinary skill in the pertinent art that modifications and variations can be made to switch  94 , but there is shown by way of example a MOSFET device, designated as MPF930 and manufactured by ON Semiconductor Phoenix, Ariz.). In another embodiment, switch  94  may be monolithically integrated in the ground fault detector  16 . 
     In response to a true ground fault or grounded neutral condition, ground fault detector  16  produces an output signal  20  during the positive half cycle portions of AC power source. The signal turns on SCR  24  and redundant SCR  88  to activate solenoid  38 . Solenoid  38  causes trip mechanism  40  to operate. 
     When a simulated grounded neutral condition is introduced in the manner described above, a test acceptance signal is provided to delay timer  86  during the negative half cycle portions of the AC power source. Delay timer  86  includes a transistor  304  that discharges capacitor  306  when the test acceptance signal is received. Capacitor  306  is recharged by power supply  18  by way of resistor  308  during the remaining portion of the AC line cycle. Again, if there is an internal failure in GFCI  10 , the test acceptance signal is not generated and transistor  304  is not turned on. As a result, capacitor  306  continues to charge until it reaches a predetermined voltage. At the predetermined voltage SCR  88  is activated during a positive half cycle portion of the AC power source signal. In response, solenoid  38  causes the trip mechanism  40  to operate. Alternatively, SCR  88  can be connected to a second solenoid  90  in the manner described in  FIG. 20 . Because  FIG. 21  is a circuit schematic of the diagram depicted in  FIG. 20 , the indicator circuit that includes indicator  91  has substantially the same or similar functionality. 
     In the exemplary circuit depicted in  FIG. 22 , both GFI  102  and checking circuit  100  derive power from power supply  18 . Redundant components can be added such that if one component has reached end of life, another component maintains the operability of GFI  102 , thereby enhancing reliability, or at least assuring the continuing operation of the checking circuit  100 . For example, the series pass element  310  in power supply  18  can include parallel resistors. Resistor  312  can be included to prevent the supply voltage from collapsing in the event the ground fault detector  16  shorts out. Clearly, if the supply voltage collapses, delay timer  86  maybe prevented from signaling an end of life condition. Those of ordinary skill in the art will recognize that there are a number of redundant components that can be included in GFCI  10 , the present invention should not be construed as being limited to the foregoing example. 
     Alternatively, SCR  88  may be connected to an end of life resistor  314  as shown by dotted line  316 , instead of being connected to solenoid  38  or  90 . When SCR  88  conducts, the value of resistor  314  is selected to generate an amount of heat in excess of the melting point of solder on its solder pads, or the melting point of a proximate adhesive. The value of resistor  314  is typically 1,000 ohms. Resistor  314  functions as part of a thermally releasable mechanical barrier. When the solder pads are melted, resistor  314  is dislodged causing the barrier to move, and trip mechanism  40  to operate. The actuation of the barrier causes interrupting contacts  42  and/or  42 ′ to be permanently open. In other words, depressing reset button  44  will not close interrupting contacts ( 42 , 42 ′). Reference is made to U.S. Pat. No. 6,621,388, which is incorporated herein by reference as though fully set forth in its entirety, for a more detailed explanation of resistor  314 . Since end of life resistor  314  affords a permanent decoupling of the load side of GFCI  10  from the AC power source, it is important that the end of life resistor  314  only dislodge when there is a true end of life condition and not due to other circumstances, such as transient electrical noise. For example, SCR  88  may experience self turn-on in response to a transient noise event. Coupling diode  318  may be included to decouple resistor  314  in the event of a false end of life condition. Coupling diode  318  causes SCR  88  to activate solenoid  38  when it is ON. Note that when the interrupting contacts are in the reset state, a circuit path is formed between the upper bus bar, through the solenoid  38  and indicator  91 , such that indicator  91  functions as a reset indicator. As noted above with respect to the earlier embodiments, indicator  91  may be implemented as part of the indicator elements  108  ( FIG. 2 ) or as part of indicator  502  ( FIG. 5 ). 
     Referring to  FIGS. 23   a - 23   g , timing diagrams illustrating the operation of the circuits depicted in  FIG. 21  and  FIG. 22  are shown.  FIGS. 23   a  through  23   e  pertain to the embodiment shown in  FIG. 21 . Referring to  FIG. 23   a , the AC power source signal is shown, having positive half cycles  400  and negative half cycles  402 . Referring to detector  16  in  FIG. 21 ,  FIG. 23   b  represents the waveform at gain output terminal  212 . Voltage signal  404  is the quiescent level when there is no grounded neutral condition, whether a simulated fault condition or true fault condition. The quiescent voltage level  404  is centered between pre-established voltage thresholds  406  and  406 ′. The threshold levels are established by ground fault detector  16 . During each negative half cycle  402 , switch  94  is closed to initiate the simulated grounded neutral signal resulting in the on-set of oscillation signal  408 . 
     The amplitude of the oscillation  410  may decay in relationship to the instantaneous voltage of power supply  18 .  FIG. 23   c  shows the output voltage signal  412  present on detector output line  20 . The duration of each output signal  412  corresponds to the interval in which the voltage at gain output terminal  212  is either greater than threshold  406 , or less than threshold  406 ′. Output signal  412  is detected by delay timer  86  as the above described test acceptance signal. 
       FIG. 23   d  represents a true grounded neutral condition that occurs in combination with the simulated grounded neutral condition. Those of ordinary skill in the art will recognize that the present invention functions equally well during a true ground fault or true arc fault condition. Referring back to  FIG. 23   d , an oscillation signal  416  is present during at least one positive half cycle  400  as a result of the fault condition.  FIG. 23   e  is a representation of the voltage signal  418  at the output of filter  22 . There are two things that are of note. First, voltage signal  418  occurs during the positive half cycle  400 . Second, once voltage  418  is greater than voltage threshold  414 , SCR  24  is turned ON, and GFI  102  is tripped out. 
       FIGS. 23   a ′,  23   f  and  23   g  pertain to the embodiment of  FIG. 22 . As described above, the embodiment of  FIG. 22  employs saturating neutral core  3 ′.  FIG. 23   a ′ is identical to  FIG. 23   a  and repeated for the reader&#39;s convenience.  FIG. 23   f  shows voltage signal  404  at the gain output terminal  212  during a simulated grounded neutral condition. Negative-tending impulses  419  corresponds to each negative half cycle of the AC power source  402 . The impulses shown in  FIGS. 23   f  and  23   g  compared to the oscillation signals shown in  FIGS. 23   b  and  23   d  produce similar results. During a true grounded neutral condition, there is additionally at least one positive-tending impulse  420  during a positive half cycle  400  of the AC power source. The results shown in  FIG. 23  are equally applicable to a true ground fault condition or a true arc fault condition. 
     Another exemplary circuit schematic is depicted in  FIG. 24 . Protective device  700  is configured to protect the electrical circuit from a plurality of fault conditions that include ground faults, grounded neutral faults, arc faults to ground, parallel arc faults between the line and neutral conductors, and series arc faults within a line or neutral conductor. Protective device  700  includes one or more additional sensors, such as sensor  702 , to detect series arc faults and parallel line to neutral arc faults, since differential transformer  2  is configured to ignore all but differential currents. In one embodiment, sensor  702  is a current sensor configured to sense the current on the hot or neutral conductor. Fault detector  704  is similar to ground fault detector  16 , but is also configured to detect and respond to other signals, such as arc recognition signatures. Output  708  operates in a manner similar to what has been described for output  20 , but further provides trip signal for the above described fault conditions during the positive half cycle portions of the AC power source. 
     Other features illustrated in  FIG. 24  include a trip indicator  706  that illuminates or annunciates when protective device  700  is tripped. The end of life lockout feature embodied in  FIG. 24  allows solenoid  38  and power supply  18  to be connected to the line side of interrupting contacts  42  without sacrificing protection if solenoid  38  reaches end of life. In particular, solenoid  38  is configured to carry current only momentarily. A shorted or opened component may result in. a continuous current being supplied. For example, this may occur when SCR  24  is shorted out. Since solenoid  38  is not coupled to the AC power source through interrupting contacts  42 , the opening of the contacts fails to limit the duration of the current to prevent overheating of the solenoid. However, the current flowing through solenoid  38  also flows through SCR  24 . As a result, SCR  88  is activated and power is applied to end of life resistor  314 . As described above, the resistor will be heated to a temperature greater than the melting point of the solder, or proximate adhesive, and the resistor  314  will fail. Of course, this results in a lock-out condition wherein interrupting contacts  42  are permanently opened. Thus, the end of life lockout feature is effective even if solenoid  38  is impaired through over activation. 
     In yet another feature, an auxiliary impedance  710 , preferably including an inductance, couples power from the AC power source to polarity detector  92  and miswire network  46 . The value of impedance  710  is chosen to be greater than 50 ohms in the presence of high frequency impulse noise on the electrical circuit, such as caused by lightning activity. The impedance permits a small metal oxide varistor  15 ′, rated less than one Joule, to protect polarity detector  92  and miswire network  46  from damage. Likewise, the inductance of solenoid  38  is chosen such that snubber network  36  protects SCR  24  and power supply  18  from damage. The use of an auxiliary impedance in combination with other impedances, such as the impedance of a solenoid, is an alternative design that avoids using an across-the-line metal oxide varistor such as MOV  15  in  FIG. 20 . An across-the-line varistor is typically greater than 12 mm in size. The excessive size is a result of a requirement that the varistor successfully absorb the full energy of the voltage impulse. As shown, auxiliary impedance  710  is a stand-alone component, but could have been shown as sharing one of the magnetic cores of the inductors that have been previously described. 
     Like some of the previous embodiments described herein, GFCI  700  includes a wiring state detection circuit  46  which is shown in the &#39;522 patent. Circuit  46  describes a wiring state detection indicator  706 . The &#39;522 patent includes four embodiments that further include various wiring state detection circuits and indicators, all of which are incorporated herein as though fully set forth in their entirety. 
     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. 
     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. 
     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. 
     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. 
     No language in the specification should be construed as indicating any non-claimed element as essential to the practice of the invention. 
     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.