Abstract:
The present invention is directed to a protective device that includes a plurality of line terminals and a plurality of load terminals, the plurality of load terminals including a plurality of hot load terminals and a plurality of neutral load terminals. The device also includes a circuit interrupter having four sets of moveable contacts, the four sets of moveable contacts being configured to couple the plurality of line terminal to the plurality of load terminals in a reset state and to decouple the plurality of line terminals from the plurality of load terminals in a tripped state. A test circuit includes an end of life detection circuit coupled to the plurality of line terminals or the plurality of load terminals by a switch mechanism associated with the four sets of moveable contacts. The test circuit includes a manually actuatable button and a fusible element, the fusible element assuming a permanently open state if the circuit interrupter does not enter the tripped state within a predetermined period after the manually actuatable button has been actuated.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This is a continuation of U.S. patent application Ser. No. 12/235,380 filed on Sep. 22, 2008, which is a continuation of U.S. patent application Ser. No. 11/382,345 filed on May 9, 2006 which is a continuation of U.S. patent application Ser. No. 10/729,392 filed on Dec. 5, 2003, now U.S. Pat. No. 7,068,481, which is a continuation of U.S. patent application Ser. No. 10/263,028 filed on Oct. 2, 2002, now abandoned, the contents of which are 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. 10/263,028 claims priority to Provisional Patent Application Ser. No. 60/326,531, filed on Oct. 2, 2001. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates generally to the field of devices for protecting electrical circuits in the event of faults, and more particularly to a device that protects from arc faults and ground faults. 
     2. Technical Background 
     The electrical distribution system is defined to include the circuit breaker, branch circuit conductors, wiring devices, cord sets or extension cords, and electrical conductors within an appliance. A protective device is incorporated in an electrical distribution system for protecting a portion of the system from electrical faults. Ground fault circuit interrupters, also called GFCIs, are one type of protective device that has become quite widely used. They 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. 
     Arc fault circuit interrupters, also called AFCIs, are another type of protective device but that has been in use more recently. 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 that has been considered, 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 that has been considered, 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. 1 . 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 an SCR  22  which 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 which 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. 2 , the mechanical layout for the circuit diagram of  FIG. 1  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. 3 , the mechanism of  FIG. 2  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 which returns armature  32  to a resting position against solenoid  24 , opening contacts  35  and  37  and disconnecting power to the load. 
     Protective devices have been located in an electrical distribution system in a variety of conventional device housings such as but not limited to circuit breakers typically installed inside a panel at the service entrance having an interrupting contact that disconnects the load in response to sustained overcurrent, receptacle outlets or snap switches typically installed inside a wall box, portable housings typically installed in plugs or connectors or as protective modules within appliances. Constructional requirements for the different device housings differ. Some differences arise from the pertinent UL (Underwriters Laboratories) safety standards, for example, UL standard 943 for GFCIs and UL standard 1699 for AFCIs. Unlike circuit breaker and receptacle devices, portable devices are susceptible to a poor connection between the receptacle and neutral plug blade. Therefore, only portable devices must continue to afford provide protection or interrupt load side power due to neutral supply conductor failure. This requirement for the portable protective device has often been accomplished using a relay with normally open contacts serving as the circuit interrupter. Other differences arise from the nature of the housing itself, wherein protective devices that are housed in a circuit breaker and that require a power supply most conveniently derive power for the supply power from the load side of the circuit interrupter. 
     Some of the protective devices discussed above employ complicated circuitry that is both expensive and subject to failure. Some of the protective devices that have been considered by designers may include complicated mechanical linkages. Some of the devices under consideration may require a power supply for powering the protective circuitry, the power being derived from the line terminals of the protective device. Inconveniently, the protective device is housed in a circuit breaker enclosure and the circuit breaker derives power from the load side terminals of the protective device. 
     SUMMARY OF THE INVENTION 
     Briefly stated, the present invention is directed to a protective device that addresses the needs described above. In particular, the present invention provides a test facility that drives the device both into a tripped state and into a reset lockout state in response to the detection of an end of life condition. The test facility determines that the device has failed by monitoring its response to a simulated fault condition. 
     One aspect of the present invention is directed to a electrical wiring device that includes a plurality of line terminals and a plurality of load terminals. A sensor is coupled to the plurality of line terminals or the plurality of load terminals. The at least one sensor provides a sensor output signal corresponding to electrical perturbations propagating on the plurality of line terminals or the plurality of load terminals. A fault detection circuit is coupled to the sensor, the fault detection circuit being configured to generate a fault detection signal if the sensor output signal substantially corresponds to at least one predetermined fault criterion. An actuator assembly is responsive to the fault detection signal, the actuator assembly including a breaker coil configured to generate an actuation force in response to being energized. A circuit interrupter is coupled to the actuator assembly, the circuit interrupter including four sets of movable contacts configured to be driven into a reset state in response to a reset stimulus, the four sets of movable contacts being configured to be driven into a tripped state in response to the actuation force. A reset mechanism includes a reset button configured to provide the reset stimulus. A test assembly is coupled to the reset mechanism, the test assembly including a test circuit coupled to a reset lockout mechanism, the test circuit including a circuit portion coupled to at least one of the plurality of line terminals or the plurality of load terminals by a switch element, the switch element being closed in the reset state by operation of the reset mechanism and opened in the tripped state, the circuit portion being substantially isolated from the plurality of line terminals and the plurality of load terminals in the tripped state, the test circuit being configured to generate a simulated fault condition in response to a user input, the reset lockout mechanism being configured to trip the circuit interrupter and disable the reset mechanism if any one of the sensor, fault detection circuit, actuator assembly, or circuit interrupter assembly fail before a predetermined time elapses. 
     Another aspect of the invention is directed to a protective device that includes a plurality of line terminals and a plurality of load terminals, the plurality of load terminals including a plurality of hot load terminals and a plurality of neutral load terminals. The device also includes a circuit interrupter having four sets of moveable contacts, the four sets of moveable contacts being configured to couple the plurality of line terminal to the plurality of load terminals in a reset state and to decouple the plurality of line terminals from the plurality of load terminals in a tripped state. A test circuit includes an end of life detection circuit coupled to the plurality of line terminals or the plurality of load terminals by a switch mechanism associated with the four sets of moveable contacts. The test circuit includes a manually actuatable button and a fusible element, the fusible element assuming a permanently open state if the circuit interrupter does not enter the tripped state within a predetermined period after the manually actuatable button has been actuated. 
     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  shows a circuit diagram for a ground fault circuit interrupter (GFCI) according to the prior art; 
         FIG. 2  shows a partial sectional view of a prior mi mechanical implementation of the schematic of  FIG. 1 ; 
         FIG. 3  shows the mechanical implementation of  FIG. 2  in the tripped state; 
         FIG. 4  shows a partial sectional view of a mechanical implementation of an embodiment of the invention; 
         FIG. 5  shows a partial sectional view of the mechanical implementation of  FIG. 4  is shown in the lock-out position; 
         FIG. 6  shows a three-dimensional view of some of the components of the embodiment of  FIG. 4 ; 
         FIG. 7  shows a protective device according to an embodiment of the invention; 
         FIG. 8  shows a protective device according to an embodiment of the invention; 
         FIG. 9  shows a protective device according to an embodiment of the invention; 
         FIG. 10  shows a protective device according to an embodiment of the invention; 
         FIG. 11  shows a protective device according to an embodiment of the invention; 
         FIG. 12  shows a protective device according to an embodiment of the invention; and 
         FIG. 13  shows a protective device according to an embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION 
     Reference will now be made in detail to the present exemplary embodiments of the invention, examples of which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or like parts. An exemplary embodiment of the GFCI of the present invention is shown in  FIGS. 4-13  and is designated generally throughout by reference numeral  2 . 
     As embodied herein and depicted in  FIG. 4 , a partial sectional view of a mechanical implementation of an embodiment of the invention is shown. A resistor  8 ′, shown schematically in  FIG. 1  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 120 V AC supply is required by UL to be 15 K-Ohms, which dissipates nominally 0.96 Watts 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. 5 , a partial sectional view of the mechanical implementation of  FIG. 4  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 which 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 . Thus resistor  8 ′ is integral to the lock-out feature of the present invention. 
     Referring to  FIG. 6 , components of the embodiment of  FIG. 4  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. 7 , a protective device  710  shows a resistor  700  which is then used as the resistor body which constrains spring  400 . There are other ground fault circuit interrupters whose trip thresholds are greater than 6 milliamperes intended for a variety of supply voltages or phase configurations, and intended for personnel protection or fire prevention. Alternate trip levels typically include 30 milliamperes in the U.S. or Europe, or 300 or 500 milliamperes in Europe, to which the invention as described applies. 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  from 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. 7  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. 7  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. 8 , a protective device  810  which is an alternate embodiment to  FIG. 7  shows a resistor  800  which serves the same function as resistor  700  in  FIG. 7  but is coupled to the load side of the interrupting contacts, i.e., contact armatures  32 ,  34 . This may be important for 6 milliamperes 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. 7  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. 8  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. 9 , a protective device  910  which is an alternative embodiment to  FIG. 8  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. Note that the bus bar arrangement includes four sets of movable interrupting contacts. Resistor  900  serves the same function as resistor  800  in  FIG. 8  except that resistor  900  is coupled to moveable bus bar  902 ′. Note that bus bar &#39; 902  functions as an auxiliary switch mechanism coupling the circuit portion that includes resistor  900  the line terminals ( 3 ,  5 ) and the load terminals ( 37 ,  39 ) in the reset state. Moreover, when the circuit interrupter is tripped, the auxiliary switch mechanism of bus bar &#39; 902  substantially isolates resistor  900  from the line terminals ( 3 ,  5 ) and the load terminals ( 37 ,  39 ) by introducing an air gap between resistor  900  and the neutral conductors. 
     For receptacle housings it is possible for the installer to mis-wire a GFCI such that the supply voltage is connected to load terminals  37  and  39 , which would cause resistor  800  ( FIG. 8 ) 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. 9  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. Mis-wiring thus does not cause a permanent lock-out of device  910 . 
     Referring to  FIG. 10 , a protective device  1010  which is an alternate embodiment to  FIG. 7  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. 7 , i.e., resistor  1004  is normally in such a position as to leave spring  400  ( FIG. 6 ) 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. 10  shows an alternative to  FIG. 8  wherein a hazardous current does not occur when the hot and neutral supply conductors are inadvertently transposed as described in  FIG. 8 . In addition,  FIG. 10  shows another remedy for the issue described in the  FIG. 9  embodiment wherein resistor  1004  melts solder only if protective device  1010  is non-operational and not when protective device  1010  is mis-wired. 
     Referring to  FIG. 11 , 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. 1-5 , 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. 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. 12 , elements of the circuit diagram of  FIG. 11  are combined with elements of the circuit diagram of  FIG. 8  in a protective device  1210 , wherein components having like functions bear like numbers. The concept shown in  FIG. 11  is thus combined with the embodiment of  FIG. 8  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. 13 , 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. 1 ) 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. 1 ), 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. 7 ) 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. 4 ), wherein lockout spring  400  causes armatures  32  and  34  to be permanently disconnected. 
     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.