Abstract:
A circuit interrupting device having an auto-monitoring circuit for periodically testing various functions and structures of the device. The auto-monitoring circuit initiates an auto-monitoring routine which, among other things, generates a self-test fault condition and determines whether the detection mechanisms within the device properly detect the self-test fault. Processing an early detection signal determines whether the self-test fault was properly detected without interfering with the normal operation of the detection circuitry and without causing a false trip within the device. Additional functionality of the auto-monitoring circuit permits automatic verification that the device is properly wired, that is, not miswired, and determines whether the device has reached the end of its useful life.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application contains subject matter related to subject matter contained in copending U.S. patent application Ser. No. 13/422,797, titled, “SOLENOID COIL HAVING AN ENHANCED MAGNETIC FIELD,” by Stephen P. Simonin, U.S. patent application Ser. No. 13/422,790, titled, “ENHANCED AUTO-MONITORING CIRCUIT AND METHOD FOR AN ELECTRICAL DEVICE,” by Gaetano Bonasia and Kenny Padro and U.S. patent application Ser. No. 13/422,793, titled “REINSTALLABLE CIRCUIT INTERRUPTING DEVICE WITH VIBRATION RESISTANT MISWIRE PROTECTION,” by Gaetano Bonasia et al., which applications are assigned to the assignee hereof, and the entire contents of each of which are expressly incorporated herein by reference. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates generally to switched electrical devices. More particularly, the present invention is directed to self-testing circuit interrupting devices, such as ground fault circuit interrupter (GFCI) devices, that switch to a “tripped” or unlatched state from a “reset” or latched state when one or more conditions is detected. Such devices consistent with the invention disclosed herein have more robust self-testing capabilities than provided in previously known GFCI devices. 
         [0004]    2. Description of Related Art 
         [0005]    GFCI devices having contacts that are biased toward the open position require a latching mechanism for setting and holding the contacts in a closed position. Likewise, switched electrical devices having contacts that are biased toward the closed position require a latching mechanism for setting and holding the contacts in an open position. Examples of conventional types of devices include devices of the circuit interrupting type, such as circuit breakers, arc fault interrupters and GFCIs, to name a few. 
         [0006]    To be commercially sold in the United States a GFCI device must conform to standards established by the Underwriter&#39;s Laboratory (UL) in conjunction with industry-leading manufacturers as well as other industry members, such as various safety groups. One UL standard covering GFCI devices is UL-943, titled “Standard for Safety—Ground Fault Circuit Interrupters.” UL-943 applies to Class A, single- and three-phase, GFCIs intended for protection of personnel and includes minimum requirements for the function, construction, performance, and markings of such GFCI devices. UL-943 requires, among other things, specific fault current levels and response timing requirements at which the GFCI device should trip. Typically, GFCIs are required to trip when a ground fault having a level higher than 5 milliamps (mA) is detected. Further, when a high resistance ground fault is applied to the device, the present version of UL-943 specifies that the device should trip and prevent current from being delivered to the load in accordance with the equation, T=(20/I) 1.43 , where T refers to time and is expressed in seconds and I refers to electrical current and is expressed in milliamps. Thus, in the case of a 5 mA fault, the device must detect the fault and trip in 7.26 seconds or less. 
         [0007]    With such safety-related standards in place, and because GFCI devices are directly credited with saving many lives since their introduction in the early 1970s, they have become ubiquitous throughout the residential and commercial electrical power grid. Like most electro-mechanical devices, however, GFCI devices are susceptible to failure. For example, one or more of the electronic components that drive the mechanical current interrupter device can short-out or otherwise become defective, as can components in the fault detector circuit or elsewhere within the device, rendering the device unable to properly detect the ground fault and/or properly interrupt the flow of electrical current. For this reason it has long been required that GFCI devices be provided with a supervisory circuit that enables manual testing of the ability of the device to trip when a fault is encountered. Such supervisory circuits are typically have a TEST button which, when pressed, actuates a simulated ground fault on the hot and neutral conductors. If the device is functioning properly the simulated fault is detected and the device will trip, i.e., the mechanical interrupter is actuated to open the current path connecting the line side of the device, e.g., where the in AC power is supplied, and load side, where the user connects his or her electrical appliance, etc. and where downstream receptacles or additional GFCI devices are connected. 
         [0008]    A study performed by industry safety groups indicated that most often the public does not regularly test their GFCI devices for proper operation, i.e., by pressing the TEST button. This study further revealed that some GFCI devices that had been in service for an extended period of time became non-functional and were unable to properly detect a fault condition, thus, rendering the device unsafe. Specifically, it was discovered that after extended use GFCI devices fail to trip when a fault occurs, thus rendering the device operable as an electrical receptacle but unsafe in the presence of a fault condition. Because the devices are not being regularly tested, this unsafe condition is exacerbated. That is, people falsely believe the device is operational, in view of the fact that it adequately delivers power, when in fact the device is a potentially life-threatening hazard. 
         [0009]    The discovery that GFCI devices deployed in the field are becoming increasingly non-operational and unsafe in combination with the realization that people do not regularly test their GFCI devices, regardless of manufacturer&#39;s explicit instructions to do so, initiated investigations into possible changes to the UL-943 standard to require the GFCI devices to self-test (e.g., auto-monitor) themselves without the need for human intervention. The changes contemplated to UL-943 further included a requirement for either a warning to the consumer of the loss of protection and/or the device automatic removing itself from service, e.g., permanently tripping. Moreover, these additional self-testing operations would have to be performed without interfering with the primary function of the device, i.e., tripping when an actual fault was encountered. 
         [0010]    The revised self-test functionality mentioned above is not yet a requirement for UL-943 certification, but it is expected that it will be soon. In preparation for this significant UL change, and in view of the seemingly endless reduction in the cost of integrated circuits, many GFCI manufacturers have migrated to digital techniques (e.g., microprocessors and microcontrollers) in favor of previous analog designs to provide both ground fault protection and self-monitoring functionality. The digital solutions offered thus far, however, are not ideal. For example, several related art GFCI designs, including those directed at providing self-test functionality, suffer from nuisance tripping, a situation where the interrupter is actuated when neither a real ground fault, a manually generated simulated ground fault, nor an automatic self-test fault are present. This unfavorable condition is believed by many to be worsened by the additional requirement of automatic self-testing, which results in additional inductive currents being generated within the device. 
         [0011]    It is therefore desired to provide a GFCI device that provides certain self-testing capabilities, including those proposed in the next revision of UL-943, but minimizes the risks associated with nuisance tripping. 
       SUMMARY OF THE INVENTION 
       [0012]    In consideration of problematic issues associated with related art GFCI devices, including but not limited to the problematic issues discussed above, a circuit in accordance with one or more exemplary embodiments of the present invention generally relates to an auto-monitoring circuit that continuously monitors the performance of a GFCI device. More specifically, a processing device, such as a microcontroller or microprocessor, is configured to periodically perform an auto-monitoring routine based on a stored software program for testing and verifying the viability and functionality of various sub-circuits within the GFCI device. To test proper current isolation of the GFCI device, a driver coupled to the microcontroller is operated to initiate a test signal representative of a ground fault each time the auto-monitoring routine is performed, or run, and different circuit nodes are monitored to confirm proper operation of the device. 
         [0013]    An end-of-life indicator is also coupled to the microcontroller to indicate whether the GFCI device has failed to properly detect the test signal or some other malfunction within the device has occurred. To avoid tripping the mechanical current-interrupting device when the test signal is generated, but also allow as much of the GFCI device circuitry to perform its intended function, a unique monitor circuit is provided that takes advantage of various functionality of the digital components, such as the GFCI integrated circuit device and the microcontroller. Specifically, to provide an automatic test function that monitors the fault detection capability of the GFCI device without interfering and causing a false trip under normal conditions, embodiments consistent with the invention include a specifically selected filter capacitor associated with the interrupter drive output of the GFCI integrated circuit (IC) device. Proper selection of the capacitor and other related circuit components prevents the interrupter drive circuit, e.g., silicon controlled rectifier (SCR), from firing, or turning ON, until a real fault condition is encountered. 
         [0014]    In accordance with one aspect of the invention a circuit interrupting device is provided that includes one or more line conductors for electrically connecting to an external power supply, one or more load conductors for electrically connecting to an external load, an interrupting device connected to the line conductors and the load conductors and electrically connecting the line conductors to the load conductors when the circuit interrupting device is in a reset condition and disconnecting the line conductors from the load conductors when the circuit interrupting device is in a tripped condition. A fault detection circuit is also provided that detects a fault condition in the circuit interrupting device and generates a fault detection signal when the fault condition is detected, wherein the fault detection signal is provided to the interrupting device to place the circuit interrupting device in the tripped condition. An auto-monitoring circuit is electrically coupled to the fault detection circuit and the interrupting device and continuously monitors one or more signals to determine an operating state of the circuit interrupting device, wherein at least one of the monitored signals includes a first auto-monitoring input signal the value of which is at least partially determined by a value of a pre-trigger signal generated by the fault detection circuit, wherein the pre-trigger signal does not activate the interrupting device to place the circuit interrupting device in the tripped condition. 
         [0015]    According to another aspect of the invention a circuit interrupting device is provided that includes a wiring device having a fault detection circuit configured to detect one or more fault conditions in the wiring device and generate a pre-trigger signal when the fault condition meets predetermined criteria, wherein the one or more fault conditions includes a self-test fault condition. A programmable circuit device is also provided that is programmed to execute an auto-monitoring routine that includes the steps of generating a self-test fault signal at a first output port of the programmable circuit device, wherein the self-test fault signal generates a self-test fault condition in the wiring device, input the pre-trigger signal to the programmable circuit device at a first input port, determining the value of the pre-trigger signal, processing the value of the pre-trigger signal, determining whether the fault detection circuit successfully detected the self-test fault based on the processed value of the pre-trigger signal, incrementing a failure count if it is determined that the fault detection circuit failed to successfully detect the self-test fault and resetting the failure count if it is determined that the fault detection circuit did successfully detect the self-test fault. 
         [0016]    According to a further aspect of the invention a method of monitoring the operational state of an electrical wiring device is provided where the method includes the steps of periodically generating a self-test fault signal, detecting the self-test fault signal, generating a pre-trigger signal when the self-test fault signal is detected, incrementing a counter if the value of the pre-trigger signal is greater than or equal to a first threshold, resetting the counter if the value of the pre-trigger signal is less than the first threshold; determining that either a real fault condition or a simulated fault condition has occurred if the value of the pre-trigger signal is greater than a second threshold less than the first threshold, ceasing generation of the self-test fault signal if it is determined that either a real fault condition or a simulated fault condition has occurred, and continuing generation of the self-test fault signal if it is determined that either a real fault condition or a simulated fault condition has not occurred. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0017]    Exemplary embodiments of the disclosed invention are described in detail below by way of example, with reference to the accompanying drawings, in which: 
           [0018]      FIG. 1  is a side elevation view of a self-testing GFCI receptacle device in accordance with an exemplary embodiment of the present invention; 
           [0019]      FIG. 2  is a side elevation view of the self-testing GFCI receptacle shown in  FIG. 1  with the front cover of the housing removed; 
           [0020]      FIG. 3  is a side elevation view of a core assembly of the self-testing GFCI receptacle device shown in  FIG. 1 ; 
           [0021]      FIG. 4  is a schematic of an exemplary circuit consistent with an exemplary embodiment of the present invention; 
       
    
    
     DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS 
       [0022]    Exemplary embodiments of devices consistent with the present invention include one or more of the novel mechanical and/or electrical features described in detail below. For example, one or more of the exemplary embodiments of the invention disclosed include auto-monitoring or, self-test, features. Some self-test features and capabilities with respect to GFCI devices have been disclosed previously, for example, in U.S. Pat. Nos. 6,807,035, 6,807,036, 7,315,437, 7,443,309 and 7,791,848, and U.S. patent application Ser. No. 13/422,790, filed on Mar. 16, 2012, all which are commonly assigned to the same assignee of this application and the entire respective contents of which are incorporated herein by reference for all that is taught. An auto-monitoring feature consistent with the present invention disclosed herein is more robust than that which has been previously disclosed and reduces the probability of false or nuisance tripping by the device. For example, additional features are provided that relate to the determination of an end-of-life (EOL) condition and actions taken subsequent to such determination. Further exemplary novel electrical and mechanical features consistent with the invention are described herein below with reference to the figures. 
         [0023]    Referring to  FIG. 1 , a GFCI receptacle  10  according to an exemplary embodiment of the invention includes a front cover  12  having a duplex outlet face  14  with phase  16 , neutral  18  and ground  20  openings. Face  14  also has opening  22  accommodating RESET button  24  adjacent opening  26  accommodating TEST button  28  and six respective circular openings,  30 - 35 . In accordance with this exemplary embodiment openings  30 ,  33  accommodate two respective indicators, such as different colored LEDs, openings  32 ,  34  accommodate respective bright LEDs used, for example, as a nightlight, opening  31  accommodates a photoconductive photocell used, for example, to control the nightlight LEDs, and opening  35  provides access to a set screw for adjusting a photocell device in accordance with this and other exemplary embodiments. Rear cover  36  is secured to front cover  12  by eight fasteners  38 —four fasteners  38  are shown in  FIG. 1  and four additional fasteners are provided on the side of receptacle  10  obscured from view in  FIG. 1 . For example, each fastener  38  may include a barbed post  50  on front cover  12  and corresponding resilient hoop  52  on rear cover  36 , similar to that which is described in detail in U.S. Pat. No. 6,398,594, the entire contents of which are incorporated herein by reference for all that is taught. Ground yoke/bridge assembly  40  having standard mounting ears  42  protrudes from the ends of receptacle  10 . 
         [0024]    Referring to  FIG. 2 , front cover  12  has been removed to expose manifold  126 , which provides support for printed circuit board  390  and yoke/bridge assembly  40 . According to the embodiment shown, manifold  126  includes four dovetail interconnects  130  that mate with corresponding cavities  132  along the upper edge of rear cover  36 . One dovetail-cavity pair is provided on each of the four sides of manifold  126  and rear cover  36 , respectively. 
         [0025]      FIG. 3  is a side elevation view of core assembly  80 . Core assembly  80  includes circuit board  82  that supports most of the working components of the receptacle, including the circuit shown in  FIG. 4 , sense transformer  84  and grounded neutral transformer  85  (not shown). Line contact arms  94 ,  96  pass through transformers  84 ,  85  with an insulating separator  98  therebetween. Line contact arms  94 ,  96  are cantilevered, their respective distal ends carrying phase and neutral line contacts  102 ,  104 . Load contact arms  98 ,  100  are also cantilevered with their respective distal ends carrying phase and neutral load contacts  101 ,  103 . The resiliency of the cantilevered contact arms biases the line contacts  102 ,  104  and load contacts  101 ,  103  away from each other. Load contact arms  98 ,  103  rest on a movable contact carriage  106 , made of insulating (preferably thermoplastic) material. 
         [0026]      FIG. 4  is a schematic drawing of the electrical and mechanical components of a GFCI receptacle device consistent with one or more of the exemplary embodiments of the present invention. The circuit shown in  FIG. 4  can be employed in a GFCI device as described above with respect to various embodiments of the invention. The circuit of  FIG. 4  is consistent with the mechanical operation of the exemplary embodiments described above; however, a GFCI device consistent with embodiments of the invention need not employ the precise electrical circuit depicted in  FIG. 4  and those of ordinary skill in the art, after viewing  FIG. 4  and/or reviewing the description set forth below, would be able to modify certain aspects of the circuit to achieve similar overall results. Such modifications are contemplated and believed to be within the scope of the invention set forth herein. 
         [0027]      FIG. 4  is a schematic drawing of an electrical circuit in accordance with an exemplary embodiment of the invention. The circuit shown in  FIG. 4 , or various sub-circuits thereof, can be implemented in a variety electrical wiring devices, however, for purposes of description here the circuit of  FIG. 4  is discussed in conjunction with its use in the GFCI receptacle device shown in  FIGS. 1-3 . 
         [0028]    The circuit of  FIG. 4  includes phase line terminal  326  and neutral line terminal  328  for electrical connection to an AC power source (not shown), such as a 60-hertz, 120 volt rms power source as used in the United States for mains power. The circuit of  FIG. 4  and the software resident on and implemented therewith, can be modified to accommodate other power delivery systems as well. Such modifications and the resultant circuit and wiring device in which the circuit and software are would ultimately be used are contemplated by the inventor and considered to be within the spirit and scope of the invention described herein. For example, power delivery systems that use different voltages and frequencies are within the scope of the invention. 
         [0029]    Referring to  FIG. 4 , phase conductor  330  and neutral conductor  332  are respectively connected to the phase and neutral line terminals and each pass through sense transformer  334  and grounded neutral transformer  336 , which are part of a detection circuit described below. By way of example, phase and neutral line terminals correspond to input terminal screws  326 ,  328  in  FIG. 1  above and phase and neutral line conductors  330 ,  332  represent line contact arms  94 ,  96 , respectively, as described above with respect to  FIG. 3 . Each of line conductors  330 ,  332  has a respective fixed end connected to the phase and neutral line terminals and each includes a respective movable contact, e.g. contacts  102 ,  104  from the embodiment described above. Face phase and face neutral conductors  338 ,  340 , respectively, include electrical contacts (not shown) fixed thereto. The face conductors are electrically connected to and, in the embodiment shown are integral with, respective face terminals  342 ,  344 , to which plug blades from a load device (not shown), such as an electrical appliance, would be connected when the electrical receptacle device is in use. 
         [0030]    The circuit shown in  FIG. 4  according to this embodiment also includes optional load phase and load neutral terminals  346 ,  348 , respectively, which electrically connect to a downstream load (not shown), such as one or more additional receptacle devices. Load terminals  346 ,  348  are respectively connected to cantilevered load conductors  277 ,  278 , each of which includes a movable contact (not shown in  FIG. 4 ) at its distal end. The load contacts are disposed below respective phase and neutral line contacts and phase and neutral face contacts and are coaxial with them such that when the line conductors are moved toward the load and face conductors, the three sets of contacts mate and are electrically connected together. When the device is in this condition it is said to be “reset” or in the reset state. 
       The Detector Circuit 
       [0031]    With continued reference to  FIG. 4 , detector circuit  352  includes transformers  334 ,  336  as well as a GFCI integrated circuit device (GFCI IC),  350 . In accordance with the present embodiment GFCI IC  350  is the well-known 4141 device, such as an RV4141 device made by Fairchild Semiconductor Corporation. Other GFCI IC devices could also be used in the circuit of  FIG. 4  instead of the 4141 and such a modification is within the spirit and scope of the invention. 
         [0032]    GFCI IC device  350  receives electrical signals from various other circuit components, including transformers  334 ,  336 , and detects one or more kinds of faults, such as a real fault, a simulated fault or self-test ground fault, as well as a real or simulated grounded neutral fault. For example, when a sufficient current imbalance in line conductors  330 ,  332  occurs, a net current flows through the transformers  334 ,  336 , causing a magnetic flux to be created about at least transformer  334 . This magnetic flux results in electrical current being induced on conductor  333 , which is wound around sense transformer  334 . Respective ends of conductor  333  are connected to the positive and negative inputs to the sense amplifier of GFCI IC device  350  at input ports V-REF and VFB, respectively. The induced current on conductor  333  causes a voltage difference at the inputs to the sense amplifier of GFCI IC  350 . When the voltage difference exceeds a predetermined threshold value, a detection signal is generated at one or more of outputs of GFCI IC  350 , such as the SCR trigger signal output port (SCR_OUT). The threshold value used by GFCI IC  350  is determined by the effective resistance connected between the op-amp output (OP_OUT) and the positive input to the sense amplifier (VFB). 
         [0033]    The current imbalance on line conductors  330 ,  332  results from either a real ground fault, a simulated ground fault or a self-test ground fault. A simulated ground fault is generated when test switch  354  in  FIG. 4  closes, which occurs when TEST button  28  ( FIG. 1 ) is pressed. As described in further detail below, a self-test fault occurs when auto-monitoring circuit  370  initiates an auto-monitoring test sequence that includes an electrical current being generated on independent conductor  356 . 
         [0034]    According to the present embodiment, when test switch  354  closes, some of the current flowing in line conductors  330 ,  332  and load conductors  338 ,  340  is diverted from the phase face conductor  338  (and phase load conductor  277  when the device is in the reset state) around sense transformer  334  and through resistor  358  to neutral line conductor  332 . By diverting some of the current through resistor  358  in this manner, an imbalance is created in the current flowing through conductor  330  and the current flowing in the opposite direction through conductor  332 . When the current imbalance, i.e., the net current flowing through the conductors passing through the sense transformer, exceeds a threshold value, for instance 4-5 milliamps, this simulated ground fault is detected by detector circuit  352  and the SCR output of GFCI IC  350  (SCR_OUT) is activated. 
         [0035]    When the SCR output of GFCI IC  350  is activated, the gate of SCR  360  is turned ON allowing current to flow from the phase line conductor  330  through diode  359  and SCR  360 . The current flowing through SCR  360  turns ON the gate of SCR  361  and SCR  369 . When SCR  361  is turned ON, current flows from phase line conductor  330  through secondary coil  363  of dual-coil solenoid  362 , fuse  365 , diode  367  and SCR  361 . Further, when SCR  369  is turned ON, current flows from phase line conductor  330  through primary coil  364  of dual-coil solenoid  362 , fuse  372 , diode  374  and SCR  369 . The current flowing through both coils  363 ,  364  generates a magnetic field that moves an armature within solenoid  362 . When the solenoid armature moves, it unlatches a contact carriage, (e.g.,  106  in  FIG. 3 ) which is part of interrupting device  315 , and the carriage drops under the natural bias of line conductors  330 ,  332 , that is, away from the face conductors  338 ,  340  and load conductors  277 ,  278 . The device is now said to be “tripped,” as a result of the successful manual simulated fault test sequence, and the device will not deliver power to a load until it is reset. The time it takes from the instant switch  354  closes until the device is tripped and current no longer flows from phase line conductor  330  to either the face and load conductors and through solenoid coils  363 ,  364 , is so short that fuses  365 ,  372  remain intact. 
       Manual Testing Via the Reset Operation 
       [0036]    With continued reference to  FIG. 4 , closing reset switch  300 , e.g., by pressing RESET button  24  ( FIG. 1 ), also initiates a test operation. Specifically, when reset switch  300  closes, a voltage supply output, VS, of GFCI IC  350  is electrically connected to the gate of SCR  360  through conductor  308 , thus, turning ON SCR  360 . When SCR  360  is turned ON, current is drawn from line conductor  330  through diode  359  and SCR  360  and ultimately to ground. Similar to when SCR  360  is turned ON by pressing the TEST button, as discussed previously, turning ON SCR  360  by pressing the RESET button results in SCR  361  and SCR  369  also being turned ON and current flowing through solenoid coils  363 ,  364 . The current flowing through coils  363 ,  364  of solenoid  362  generates a magnetic field at the solenoid and the armature within the solenoid is actuated and moves. Under typical, e.g., non-test, conditions, the armature is actuated in this manner to trip the device, such as when an actual fault occurs. 
         [0037]    When reset switch  300  closes, however, the device is likely already in the tripped condition, i.e., the contacts of the line, face and load conductors are electrically isolated. That is, the RESET button is usually pressed to re-latch the contact carriage and bring the line, face and load contacts back into electrical contact after the device has tripped. If the armature of solenoid  362  fails to fire when the RESET button is pressed, and the reset mechanism, including the contact carriage, fails to engage the reset plunger on its return after the RESET button is released, the device will not reset. Accordingly, if, for example, the device has not been wired to the AC power lines, or it has been mis-wired, that is, the device has been wired with the AC power not connected to the line terminals,  326 ,  328 , no power is applied to the GFCI IC  350 . If no power is applied to GFCI IC  350 , the gate of SCR  360  cannot be driven, either by the SCR output of GFCI IC  350  or when the REST button is pressed. Under this condition the device will not be able to be reset. The mis-wire condition is prevented in accordance with a wiring device consistent with the present embodiment by ensuring the device is shipped to the user in the tripped condition. Because the device cannot be reset until AC power is properly applied to the line terminals, the mis-wire condition is prevented. 
       The Auto-Monitoring Circuit 
       [0038]    With continued reference to the exemplary circuit schematic shown in  FIG. 4 , auto-monitoring circuit  370  includes a programmable device  301 . Programmable device  301  can be any suitable programmable device, such as a microprocessor or a microcontroller, which can be programmed to implement the auto-monitoring routine as explained in detail below. For example, according to the embodiment shown in  FIG. 4 , programmable device  301  is implemented by an ATMEL™ microcontroller from the ATtiny 10 family. It could also be implemented by a Microchip microcontroller such as a PIC10F204/206. 
         [0039]    According to one exemplary auto-monitoring, or automatic self-testing, routine in accordance with the embodiment shown in  FIG. 4 , microcontroller  301  initiates the auto-monitoring routine approximately every three (3) seconds by setting a software auto-monitoring test flag. The auto-monitoring test flag initiates the auto-monitoring routine within the circuit interrupting device and confirms that the device is operating properly or, under certain circumstances, determines that the circuit interrupting device has reached its end-of-life (EOL). When the auto-monitoring routine runs with a positive, i.e., successful, result, the auto-monitoring circuit enters a hibernation state until microcontroller  301  sets the test flag again and initiates another auto-monitoring routine. 
         [0040]    If the auto-monitoring routine runs with a negative result, e.g., it cannot be determined that the circuit interrupting device is functioning properly or it determines that it is, in fact, not operating properly, a failure counter is incremented and microcontroller  301  initiates another auto-monitoring routine when instructed by the software program stored in memory within the device. In addition to the failure count being incremented, a temporary indication of the failure is also provided. For example, according to the present embodiment, when such a failure occurs, I/O port GP0 of microcontroller  301  is controlled to be an output and light emitting diode (LED)  376  is controlled to flash, e.g., one or more times, to indicate the failure to a user. If the failure counter reaches a predetermined value, i.e., the auto-monitoring routine runs with a negative result a certain number of times, the number being stored and implemented in software, the auto-monitoring routine invokes an end-of-life (EOL) sequence. The EOL sequence includes one or more of the following functions; (a) indicate that EOL has been reached, for example, by continuously flashing or illuminating an indicator light and/or generating an audible sound, (b) attempt to trip the device, (c) prevent an attempt to reset the device, (d) store the EOL event on non-volatile memory, e.g., in the event there is a power failure, and (e) clear the EOL condition when the device is powered down. 
         [0041]    In accordance with this embodiment, when the auto-monitoring software determines it is time to run the auto-monitoring routine, i.e., based on the auto-monitor timer, a stimulus signal  302  is turned ON at I/O port GP1 of microcontroller  301 . When the stimulus signal is turned ON, electrical current flows through resistor  303  and a voltage is established at the base of transistor  304 , turning the transistor ON. When transistor  304  is turned ON, current flows from dc voltage supply  378  through resistor  305 , which is, for example, a 3 k-ohm resistor, and continues through electrical conductor  356  and transistor  304  to ground. Regarding dc voltage source  378 , according to the present embodiment the value of this voltage source is designed to be between 4.1 and 4.5 volts dc, but the value of this voltage supply can be any other suitable value as long as the value used is adequately taken into account for other circuit functionality described below. 
         [0042]    According to this exemplary embodiment, electrical conductor  356  is a wire, but it could also be a conductive trace on a printed circuit board. Conductor  356  is connected at one end to resistor  305 , traverses through sense transformer  334  and is looped approximately ten (10) times around the core of the transformer and connected at its other end to the collector of transistor  304 . Thus, when the software auto-monitoring test flag is set in microcontroller  301  and transistor  304  is turned ON, current flows through conductor  356  which comprises an independent conductor separate from phase line conductor  330  and neutral line conductor  332 , which also traverse through the center of sense transformer  334 . 
         [0043]    If the circuit interrupting device according to the present embodiment is functioning properly, as current flows through conductor  356  and through the sense transformer a magnetic flux is generated at sense transformer  334 . The flux generates a signal on conductor  333  which is detected by detection circuit  352 , including GFCI IC device  350 . In accordance with this embodiment, when device  350  detects the flux created at sense transformer  334 , a voltage level is increased at one of the I/O ports of device  350 , for example at the output port labeled CAP in  FIG. 4 , thus increasing the voltage on conductor  306 . 
         [0044]    According to this embodiment, capacitor  307  is connected between the CAP I/O port of microcontroller  301  and ground. As is known in the art, attaching a capacitor directly between the CAP output of a 4141 GFCI IC device and ground causes the SCR trigger signal (SCR_OUT) output from GFCI IC device  350  to be delayed by a predetermined period of time. The amount of time the trigger signal is delayed is typically determined by the value of the capacitor. According to the present embodiment, however, capacitor  307  is not connected directly between the CAP output and ground. Instead, capacitor  307  is also connected to the ADC I/O port GP0 of microcontroller  301  via a circuit path that includes diode  310  in series with resistor  311 , e.g., 3 M-Ohm, which completes a voltage divider circuit with resistor  312 , e.g., 1.5 M-Ohm. This additional circuitry connected to the capacitor at the CAP output of GFCI IC device  350  drains current from the delay capacitor. 
         [0045]    By measuring the value of the signal at ADC I/O port (GP0) and confirming it is above a certain level, it can be determined whether or not the self-test fault signal generated on conductor  356  was properly detected by detection circuit  352  and it can further be confirmed whether GFCI IC device  350  is capable of generating the appropriate SCR trigger signal. Also, to avoid tripping the device during a self-test auto-monitoring fault, the voltage at capacitor  307  is measured and proper self-test fault detection is confirmed before a drive signal is output at SCR_OUT of GFCI IC device  350 . 
         [0046]    If the current drain on capacitor  307  is too high, GFCI IC device  350  may not operate properly. For example, if as little as 3-4 microamps of current is drained from capacitor  307 , grounded neutral conditions, which are also intended to be detected by GFCI IC device  350 , may not be accurately detected, e.g., pursuant to UL requirements, because the SCR trigger signal (SCR_OUT) will not fire within the necessary amount of time. According to the present embodiment, less than about 1.3 microamps, or about 5% of the specified delay current for the GFCI IC device  350 , is drained for the ADC I/O port GP0 of microcontroller  301 . This small current drain from capacitor  307  has no effect on the ability of the device to properly detect real ground faults and/or real grounded neutral faults. 
         [0047]    According to this embodiment, approximately 50 nanoamps of current is drawn off of capacitor  307 . Parallel resistors  311  and  312  connected to the ADC I/O port GP0 of microcontroller  301  create a 4.5 megaohm drain which limits the current pulled from capacitor  307  to a maximum of 1.0 microamp. GFCI IC device  350  uses approximately 40 microamps of current to generate the SCR trigger but microcontroller  301  only requires approximately 50 nanamps to read the SCR trigger signal off of capacitor  307  before the SCR trigger signal is output from SCR_OUT. Accordingly, by selecting the proper value for capacitor  307 , in conjunction with appropriate value selections for resistors  311  and  312 , as well as diode  310 , it is possible to maintain the correct delay for the SCR trigger signal (SCR_OUT) from GFCI IC device  350  and use the ADC in microcontroller  301  to measure the signal at ADC input (GP0) to determine whether the test signal on conductor  356  has been properly detected by detection circuit  352 . 
         [0048]    It should also be noted that in the embodiment shown in  FIG. 4 , LED  376  is also connected to ADC I/O port (GP0) of microcontroller  301 . Accordingly, whether or not LED  376  is conducting or not will affect the drain on capacitor  307 , as well as the delay of the SCR trigger signal and the ability of microcontroller  301  to properly measure the signal output from the CAP I/O port of GFCI IC device  350 . Thus, in regard to the circuit shown in  FIG. 4 , LED  376  is selected such that it does not turn ON and begin conducting during the time microcontroller  301  is measuring the signal from the CAP output of GFCI IC device  350 . For example, LED  376  is selected such that its turn-ON voltage is about 1.64 volts, or higher which, according to the circuit shown in  FIG. 4 , can be measured at I/O port GP0. Additionally, to prevent any signal adding to capacitor  307  when LED  376  is being driven, diode  310  is provided. 
         [0049]    According to this embodiment, the circuit path that includes diode  310  and the voltage divider,  311 ,  312 , is connected to I/O port GP0 of microcontroller  301 , which serves as an input to an analog-to-digital converter (ADC) within microcontroller  301 . The ADC of microcontroller  301  measures the increasing voltage established by the charging action of capacitor  307 . When a predetermined voltage level is reached, microcontroller  301  turns OFF the auto-monitoring stimulus signal  302  which, in turn, turns OFF transistor  304 , stopping the current flow on conductor  356  and, thus, the flux created at sense transformer  334 . When this occurs, it is determined by microcontroller  301  that a qualified auto-monitoring event has successfully passed and the auto-monitoring fail counter is decremented if the present count is greater than zero. 
         [0050]    In other words, according to this embodiment an auto-monitoring routine is repeated by microcontroller  301  on a predetermined schedule. Based on the software program stored in memory within microcontroller  301 , the auto-monitoring routine is run, as desired, anywhere from every few seconds to every month, etc. When the routine is initiated, the flux created at sense transformer  334  occurs in similar fashion to the manner in which flux would be created if either an actual ground fault had occurred or if a simulated ground fault had been manually generated, e.g., by pressing the TEST button as described above. 
         [0051]    There is a difference, however, between an auto-monitoring (self-test) fault generated by the auto-monitoring routine and either an actual ground fault or a simulated fault generated by pressing the TEST button. When either an actual or simulated ground fault occurs, a difference in the current flowing in the phase and neutral conductors,  330  and  332 , respectively, should be generated. That is, the current on conductor  330  should be different than the current on conductor  332 . This differential current flowing through sense transformer  334  is detected by GFCI IC device  350 , which drives a signal on its SCR_OUT I/O port to activate the gate of SCR  360  and turn it ON. When SCR  360  turns ON, current is drawn through coils  363 ,  364  which causes interrupting device  315  to trip, causing the contact carriage to drop which, in turn, causes the line, face and load contacts to separate from each other. Thus, current is prevented from flowing through phase and neutral conductors  330 ,  332  to the phase and neutral face terminals  342 ,  344 , and the phase and neutral load terminals  346 ,  348 , respectively. 
         [0052]    In comparison, when the auto-monitoring routine is performed in accordance with the present invention, no differential current is created on the phase and neutral conductors  330 ,  332  and the interrupting device  315  is not tripped. Instead, during the auto-monitoring routine, the flux generated at sense transformer  334  is a result of current flowing through conductor  356 , which is electrically separated from phase and neutral conductors  330 ,  332 . The current generated on conductor  356  is present for only a brief period of time, for example, less than the delay time established by capacitor  307 , discussed previously. 
         [0053]    If the voltage established at the input to the ADC input (GP0) of microcontroller  301  reaches a programmed threshold value within this predetermined period of time during an auto-monitoring routine, it is determined that the detection circuit  352  successfully detected the current flowing through the core of sense transformer  334  and the auto-monitoring event is deemed to have passed. Microcontroller  301 , thus, determines that detection circuit  352 , including GFCI IC device  350 , is working properly. Because the current flowing through sense transformer  334  during the auto-monitoring routine is designed to be substantially similar in magnitude to the differential current flowing through the transformer during a simulated ground fault, e.g., 4-6 milliamps, it is determined that detection circuit  352  would be able to detect an actual ground fault and provide the proper drive signal to SCR  360  to trip interrupter  315 . 
         [0054]    Alternatively, auto-monitoring circuit  370  might determine that the auto-monitoring routine failed. For example, if it takes longer than the predetermined period of time for the voltage at the ADC input at GP0 of microcontroller  301  to reach the given voltage during the auto-monitoring routine, it is determined that the auto-monitoring event failed. If this occurs, an auto-monitoring fail tally is incremented and the failure is indicated either visually or audibly. According to one embodiment, the ADC port (GP0) of microcontroller  301  is converted to an output port when an auto-monitoring event failure occurs and a voltage is placed on conductor  309  via I/O port GP0, which is first converted to a output port by the microcontroller. This voltage at GP0 generates a current on conductor  309  that flows through indicator LED  376  and resistor  380  to ground. Subsequently, ADC I/O port (GP0) of microcontroller  301  is converted back to an input port and remains ready for the next scheduled auto-monitoring event to occur. 
         [0055]    According to this embodiment, when an auto-monitoring event failure occurs, indicator LED  376  illuminates only for the period of time when the I/O port is converted to an output and an output voltage is generated at that port; otherwise LED  376  remains dark, or non-illuminated. Thus, if the auto-monitoring routine is run, for example, every three (3) seconds, and an event failure occurs only a single time or sporadically, the event is likely to go unnoticed by the user. If, on the other hand, the failure occurs regularly, as would be the case if one or more of the components used in the auto-monitoring routine is permanently disabled, indicator LED  376  is repetitively turned ON for 10 msec and OFF for 100 msec by microcontroller  301 , thus drawing attention to the device and informing the user that critical functionality of the device has been compromised. Conditions that cause the auto-monitoring routine to fail include one or more of the following, open circuited differential transformer, closed circuited differential transformer, no power to the GFCI IC, open circuited solenoid, SCR trigger output of the GFCI IC continuously high, and SCR output of the GFCI IC continuously low. 
         [0056]    According to a further embodiment, if the auto-monitoring fail tally reaches a predetermined limit, for example, seven (7) failures within one (1) minute, microcontroller  301  determines that the device is no longer safe and has reached its end-of-life (EOL). If this occurs, a visual indicator is activated to alert the user that the circuit interrupting device has reached the end of its useful life. For example, when this EOL state is determined, the ADC I/O port (GP0) of microcontroller  301  is converted to an output port, similar to when a single failure is recorded as described above, and a signal is either periodically placed on conductor  309  via GP0, i.e., to blink LED  376  at a rate of, for example, 10 msec ON and 100 msec OFF, or a signal is continuously placed on conductor  309  to permanently illuminate LED  376 . The auto-monitoring routine is also halted at this time. 
         [0057]    In addition to the blinking or continuously illuminated LED  376 , according to a further embodiment when EOL is determined, an optional audible alarm circuit  382  on printed circuit board (PCB)  390  is also activated. In this situation the current through LED  376  establishes a voltage on the gate of SCR  384  such that SCR  384  is turned ON, either continuously or intermittently, in accordance with the output signal from GP0 of microcontroller  301 . When SCR  384  is ON, current is drawn from phase line conductor  330  to activate audible alarm  386  (e.g., a buzzer) providing additional notice to a user of the device that the device has reached the end of its useful life, i.e., EOL. For example, with respect to the present embodiment, audible alarm circuit  382  includes a parallel RC circuit including resistor  387  and capacitor  388 . As current is drawn from phase line conductor  330 , capacitor  388  charges and discharges at a rate controlled by the value of resistor  387  such that buzzer  386  sounds a desired intermittent alarm. 
         [0058]    A further aspect of this embodiment includes dimmable LED circuit  396 . Circuit  396  includes transistor  398 , LEDs,  400 ,  402 , light sensor  404  (e.g., a photocell) and resistors  406 - 408 . When the ambient light, e.g., the amount of light in the vicinity of the circuit interrupting device according to the present embodiment, is rising, light sensor  404  reacts to the ambient light level to apply increasing impedance to the base of transistor  398  to dim the LEDs as the ambient light increases. Alternatively, when the ambient light decreases, e.g., as night begins to fall, the current flowing through sensor  404  increases, accordingly. As the ambient light level decreases, LEDs  400  and  402  illuminate brighter and brighter, thus providing a controlled light level in the vicinity of the device. 
         [0059]    A further embodiment of the invention shown in  FIG. 4  includes a mechanism for providing microcontroller  301  with data related to whether the device is tripped or in the reset condition. As shown in  FIG. 4 , opto-coupler  392  is connected between phase and neutral load conductors  277 ,  278  and I/O port (GP3) of microcontroller  301 . Microcontroller  301  uses the value of the signal (voltage) at port GP3 to determine whether or not GFCI IC device  350  is being supplied with power and whether the device is tripped or in the reset condition. When GFCI IC device  350  is powered, e.g., via its voltage input port (LINE), which occurs when AC power is connected to line terminals  326 ,  328 , a voltage is generated at the output port (VS). This voltage is dropped across zener diode  394 , which is provided to maintain the voltage supplied to the microcontroller within an acceptable level. Diodes  366 ,  368 , connected between the phase line conductor and power supply input port (LINE) of GFCI IC  350  ensures that the voltage level supplied to GFCI IC and the VS output remain below approximately 30 volts. The voltage signal dropped across zener diode  394  is connected to input port GP3 of microcontroller  301 . If microcontroller  301  does not measure a voltage at GP3, it determines that no power is being supplied by GFCI IC device  350  and declares EOL. 
         [0060]    Alternatively, if microcontroller  301  measures a voltage at GP3, it determines whether the device is tripped or in the reset state based on the value of the voltage. For example, according to the circuit in  FIG. 4 , if the voltage at GP3 is measured to be between 3.2 and 4.0 volts, e.g., between 76% of VCC and 100% of VCC, it is determined that there is no power at the face ( 342 ,  344 ) and load ( 346 ,  348 ) contacts and, thus, the device is in the tripped state. If the voltage at GP3 is between 2.4 and 2.9 volts, e.g., between 51% of VCC and 74% of VCC, it is determined that there is power at the face and load contacts and the device is in the reset state. 
         [0061]    According to a further embodiment, when EOL is determined, microcontroller  301  attempts to trip interrupting device  315  in one or both of the following ways: (a) by maintaining the stimulus signal on third conductor  356  into the firing half-cycle of the AC wave, and/or, (b) by generating a voltage at an EOL port (GP2) of microcontroller  301 . When EOL has been declared, e.g., because the auto-monitoring routine fails the requisite number of times and/or no power is being supplied from the supply voltage output (VS) of GFCI IC device  350 , microcontroller  301  produces a voltage at EOL port (GP2). Optionally, microcontroller  301  can also use the value of the input signal at GP3, as described above, to further determine whether the device is already in the tripped state. For example, if microcontroller  301  determines that the device is tripped, e.g., the load and face contacts are not electrically connected to the line contacts, microcontroller  301  may determine that driving SCR  369  and/or SCR  361  in an attempt to open the contacts and trip the device is unnecessary and, thus, not drive SCR  369  and SCR  361  via GP2. 
         [0062]    The voltage at GP2 directly drives the gate of SCR  369  and/or SCR  361  to turn SCR  369  and/or SCR  361  ON, thus, enabling it to conduct current and activate solenoid  362 . More specifically, when SCR  369  and/or SCR  361  are turned ON, current is drawn through coil  364  of dual coil solenoid  362 . For example, dual coil solenoid  362  includes inner primary coil  364 , which comprises an 800 turn, 18 Ohm, 35 AWG coil, and outer secondary coil  363 , which includes a  950  turn, 16.9 Ohm, 33 AWG coil. Further details of the construction and functionality of dual coil  362  can be found in U.S. patent application Ser. No. 13/422,797, assigned to the same assignee as the present application, the entire contents of which are incorporated herein by reference for all that is taught. 
         [0063]    As described above, when it is determined via the auto-monitoring routine that detection circuit  352  is not successfully detecting ground faults, e.g., it does not detect the flux resulting from current flowing in conductor  356 , or it is not otherwise generating a drive signal at the SCR_OUT output port of GFCI IC device  350  to drive the gate of SCR  360  upon such detection, microcontroller  301  determines EOL and attempts to trip interrupting device  315  by methods mentioned above. Specifically, microcontroller  301  attempts to directly trip directly driving the primary coil  364 , by the back-up path GP2 to SCR 369  and SCR 361 . There is at least one difference, however, between the signal on conductor  356  when the auto-monitoring routine is being run normally, and the signal on conductor  356  generated when EOL is determined. That is, under EOL conditions, GP2 energizes both SCR 361  and SCR  369  to be triggered and coil  362  and coil  363  to be energized, thus activating solenoid  362  and  369  to trip interrupting device  315 . 
         [0064]    If interrupting device  315  is opened, or if interrupting device  315  was otherwise already open, power-on indicator circuit  321  will be OFF. For example, in the embodiment shown in  FIG. 4 , power-on indicator circuit  321  includes LED  322  in series with resistor  323  and diode  324 . The cathode of LED  322  is connected to the neutral load conductor  278  and the anode of diode  324  is connected to phase load conductor  277 . Accordingly, when power is available at the load conductors, that is, the device is powered and in the reset state, current is drawn through the power-on circuit on each alternating half-cycle of AC power, thus, illuminating LED  322 . If, on the other hand, power is not available at the load conductors  277 ,  278 , for example, because interrupting device  315  is open, or tripped, or the device is reset but no power is being applied, LED  322  will be dark, or not illuminated. 
         [0065]    Additional embodiments and aspects thereof, related to the auto-monitoring functionality consistent with the present invention, as well as further discussion of some of the aspects already described, are provided below. 
         [0066]    The sinusoidal AC waveform discussed herein is connected to the phase and neutral line terminals  326 ,  328  when the self-test GFCI device is installed correctly. According to one embodiment the AC waveform is a 60 Hz signal that includes two half-cycles, a positive 8.333 millisecond half-cycle and a negative 8.333 millisecond half-cycle. The so-called “firing” half-cycle refers to the particular half-cycle, either positive or negative, during which a gate trigger signal to SCR  360  results in the respective gates of SCR  361  and SCR  369  being driven and the corresponding respective solenoid coils  363 ,  364  conducting current, thus, “firing” solenoid  362  and causing the armature of the solenoid to be displaced. A “non-firing” half-cycle refers to the alternate half-cycle of the AC waveform, i.e., either negative or positive, during which current does not flow through the SCR or its respective solenoid coil, regardless of whether or not the SCR gate is triggered. According to the present embodiment, whether the positive or negative half-cycle is the firing half-cycle is determined by a diode, or some other switching device, placed in series with the respective solenoid coil. For example, in  FIG. 4 , diodes  359 ,  374  and  367  are configured such that the positive half-cycle is the “firing” half-cycle with respect to SCRs  360 ,  369  and  361 , respectively. 
         [0067]    According to a further embodiment of a circuit interrupting device consistent with the invention, microcontroller  301  optionally monitors the AC power input to the device. For example, the 60 Hz AC input that is electrically connected to the phase and neutral line terminals  326 ,  328  is monitored. 
         [0068]    More particularly, a full 60 Hz AC cycle takes approximately 16.333 milliseconds to complete. Thus, to monitor and confirm receipt and stabilization of the AC waveform, a timer/counter within microcontroller  301  is implemented. For example, within the three (3) second auto-monitoring window the 60 Hz input signal is sampled once every millisecond to identify a leading edge, i.e., where the signal goes from negative to positive values. When a leading edge is detected a flag is set in the software and a count is incremented. When the three (3) second test period is finished, the count result is divided by 180 to determine whether the frequency is within a specified range. For example, if the frequency is stable at 60 Hz, the result of dividing by 180 would be 1.0 because there are 180 positive edges, and 180 cycles, in three (3) seconds worth of a 60 Hz signal. If the frequency is determined to not be within a given range, for example, 50-70 Hz, the auto-monitoring self-test fault testing is stopped, but the monitoring of GP3 continues. Accordingly, a premature or errant power failure determination is avoided when a circuit interrupting device in accordance with the invention is connected to a variable power source, such as a portable generator, and the power source exhibits a lower frequency at start-up and requires a stabilization period before the optimal frequency, e.g., 60 Hz, is achieved. 
         [0069]    If the frequency is not stable at the optimal frequency, or at least not within an acceptable range, initiation of the auto-monitoring routine is delayed until the frequency is stabilized. If the frequency does not achieve the optimal frequency, or a frequency within an acceptable range, within a predetermined time, a fail tally is incremented. Similar to the fail tally discussed previously with respect to the auto-monitoring routine, if the tally reaches a given threshold, microcontroller  301  declares EOL. 
         [0070]    As described above, according to at least one exemplary embodiment, programmable device  301  is implemented in a microcontroller. Because some microcontrollers include non-volatile memory, e.g., for storing various data, etc., in the event of a power outage, according to a further embodiment, all events, timers, tallies and/or states within the non-volatile memory are cleared upon power-up of the device. Accordingly, if the fail tally or other condition resulted from, improper device installation, inadequate or improper power, or some other non-fatal condition with respect to the circuit interrupting device itself, the fail tally is reset on power-up, when the tally incrementing event may no longer be present. Another way of avoiding this potential issue in accordance with the invention is to utilize a programmable device that does not include non-volatile memory. 
         [0071]    While various embodiments have been chosen to illustrate the invention, it will be understood by those skilled in the art that other modifications may be made without departing from the scope of the invention as defined by the appended claims.