Abstract:
A combined arc fault circuit interrupter and leakage current detector interrupter. A current sensor, amplifier, and comparator are employed to detect the presence of leakage current in alternating current power conductors. Upon the detection of an amount of current leakage beyond a threshold level, a relay is opened, disconnecting a source of AC power from a power conductor being monitored, such as an appliance line cord. An arc sensor, envelope detector, amplifier, and microcontroller are employed to detect the presence of an arc fault in the alternating current power conductors. The arc fault detection algorithm implemented by the microcontroller is capable of discriminating between high frequency noise which is not caused by a parallel or series arc fault, with high frequency anomalies which are the result of arcing.

Description:
FIELD OF INVENTION 
       [0001]    The present invention relates, in general, to electrical conductor fault detection, and, specifically, to the detection of arc faults and leakage current faults in alternating current power conductors. 
       DESCRIPTION OF RELATED ART 
       [0002]    The National Electrical Code (NEC) is a widely followed safety standard regarding electrical wiring and equipment. Many state and local governments in the United States have mandated compliance with the NEC. 
         [0003]    Since the year 2002, the NEC has required that single-phase cord-and-plug-connected room air conditioners be provided with factory-installed Leakage Current Detection and Interruption (LCDI) and Arc Fault Circuit Interrupter (AFCI) protection. The LCDI or AFCI protection is required to be an integral part of the attachment plug, or be located in the power supply cord within 300 millimeters, or 12 inches, of the attachment plug. 
         [0004]    AFCI devices are designed to provide protection against parallel arcing, series arcing, or both parallel and series arcing. A series arc is a break in a single conductor where the arcing takes place between the broken conductor ends. A parallel arc is from line-to-line or line-to-ground. When an arc fault is detected, the AFCI device disconnects the appliance cord from the source of AC power. 
         [0005]    AFCI devices typically monitor an AC power line for anomalies in the line which may be characteristic or indicative of an arc fault. However, not all anomalies are characteristic of an arc fault, but are instead “normal” noise introduced into the AC power line as the result of the use of a dimmer switch or various electrical equipment. 
         [0006]    LCDI are designed to prevent electrical shock, by detecting the leakage of current from the line or neutral conductors of the AC power cord. If leakage is detected in either conductor, the LCDI device disconnects the appliance cord from the source of AC power. 
         [0007]    In view of the NEC and its widespread adoption, there is a significant need for AFCI and LCDI devices, particularly when such devices are integral with the power plug of a line cord of a room air conditioner. 
         [0008]    Accordingly, it is an object of the present invention to provide a combined AFCI/LCDI device which is integral to the power plug of a corded home appliance, such as a room air conditioner. 
         [0009]    It is another object of the present invention to provide a method for detecting electrical arcing in an alternating current carrying power conductor, wherein the method accurately discriminates between anomalies in the electrical power line-which are the result of actual arcing, versus anomalies with are not the result of arcing, such as may be caused by the presence of a dimmer switch or other devices. 
         [0010]    It is yet another object of the present invention to provide an apparatus for detecting electrical arcing in an alternating current power line, wherein the apparatus accurately discriminates between anomalies in the electrical power line which are the result of true arcing, versus anomalies with are not the result of arcing, such as may be caused by the presence of a dimmer switch. 
         [0011]    These and other objects and features of the present invention will become apparent in view of the present specification, drawings, claims and abstract. 
       BRIEF SUMMARY OF INVENTION 
       [0012]    The present invention comprises a method for detecting electrical arcing in an alternating current power line. A digital signal is produced that is indicative of a presence of detected high frequency variations in the alternating current power line. The digital signal is analyzed for the presence of at least two different criteria indicative of potential electrical arcing in the alternating current power line. An arc fault signal is generated when at least two of the at least two different criteria indicative of potential electrical arcing are determined to be present in the digital signal. 
         [0013]    Analyzing the digital signal for the presence of at least two different criteria indicative of potential electrical arcing in the alternating current power line may include analyzing the digital signal for the presence of at least three, or at least four different criteria indicative of potential electrical arcing in the alternating current power line. 
         [0014]    The digital signal that is analyzed a plurality of pulses. The analysis of the digital signal includes analyzing a quantity of pulses occurring within a predetermined window of time to determine if the quantity of pulses meets or exceeds a predetermined threshold quantity. 
         [0015]    The analysis of the digital signal further includes analyzing a plurality of adjacent pulses to determine if they have substantially different pulse widths. The analysis of the digital signal further includes analyzing a plurality of adjacent pulses to determine if they have substantially different intervals between adjacent pulses. The analysis of the digital signal further includes adding durations of intervals between a plurality of adjacent pulses together to determine if an interval duration summation exceeds a predetermined threshold. 
         [0016]    In a preferred embodiment, the present invention comprises a method for detecting both electrical arcing and leakage current in an alternating current power line, by also detecting the occurrence of a leakage current fault in the alternating current power line. 
         [0017]    The present invention also comprises an apparatus for detecting electrical arcing in an alternating current power line. The apparatus includes an arc sensor, a digital signal generator circuitry operably coupled to the arc sensor and generating at least one digital signal indicative of a presence of high frequency variations in the alternating current power line, and an analyzer operably coupled to the to the digital signal generator and capable of determining the presence of at least two different criteria indicative of potential electrical arcing in the alternating current power line. The analyzer generates an arc fault signal when at least two of the at least two different criteria indicative of potential electrical arcing are determined by the analyzer to be present in the digital signal. In a preferred embodiment, the apparatus further includes a leakage current fault detector for detecting the leakage of current from the alternating current power line. 
     
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         [0018]      FIG. 1  is a block diagram of the present AFCI/LCDI apparatus; 
           [0019]      FIG. 2  is a schematic diagram of the present AFCI/LCDI apparatus; 
           [0020]      FIG. 3  is a flow chart of a portion of the present arc fault detection method, implemented by the microcontroller of the present AFCI/LCDI apparatus; 
           [0021]      FIG. 4  is a flow chart of a portion of the present arc fault detection method, implemented by the microcontroller of the present AFCI/LCDI apparatus; 
           [0022]      FIG. 5  is waveform graph of voltage in a monitored AC power line under arcing conditions; 
           [0023]      FIG. 6  is a waveform graph of a digital signal produced by a portion of the present AFCI/LCDI apparatus in response to the monitored AC power line under the arcing conditions depicted in  FIG. 5 ; 
           [0024]      FIG. 7  is a waveform graph of voltage in a monitored AC power line showing variations in the normal sinusoidal AC waveform resulting from the use of a dimmer switch in association with the AC power line; and 
           [0025]      FIG. 8  is a waveform graph of a digital signal produced by a portion of the present AFCI/LCDI apparatus in response to the monitored AC power line under conditions depicted in  FIG. 7 . 
       
    
    
     DETAILED DESCRIPTION OF INVENTION 
       [0026]    The present AFCI/LCDI apparatus  10  is shown in  FIG. 1  as comprising arc sensor  20 , current sensor  30 , arc detection circuitry  40 , leakage current detection circuitry  50 , silicon-controlled rectifier (SCR)  60 , relay  70 , DC power supply, or regulator  80 , reset switch  90 , test switch  100 , and power indicating light emitting diode (LED)  110 . 
         [0027]    In a preferred embodiment, the apparatus is entirely contained within a relatively compact, insulating housing that serves as the power plug connected to the power cord of a household appliance, such as a room air conditioner. The power plug includes three male prongs extending from the housing to mate with a conventional female alternating current (AC) power outlet. In particular, prong  1  corresponds to the neutral portion of the AC power, prong  2  corresponds to the line (sometimes referred to as live, phase, hot or active) portion of the AC power, and prong  3  (shown in  FIG. 2 ) corresponds to the earth ground portion. Connectors  6 ,  7 , and  8  (shown in  FIG. 2 ) permit connection of the neutral, line and earth ground conductors of the appliance cable, respectively, and may be in the form, for example, of screw-down terminals. The insulated housing may further include a strain relief clamp or grommet for use in association with the appliance cable. 
         [0028]    In addition to prongs  1 ,  2  and  3 , portions of reset switch  90  and test switch  100  preferably protrude through corresponding openings in the housing, to permit manual operation of these switches. In addition, power indicating LED  110  is preferably visible through a corresponding window or aperture in the housing. All of the AFCI/LCDI circuitry are preferably contained within a single printed circuit board carried within the housing. 
         [0029]    In an alternative embodiment, the AFCI/LCDI circuitry and housing may be coupled “in-line”, as a portion of the power cord, between the AC power plug and the home appliance. In this embodiment, prongs  1 ,  2  and  3  are replaced with suitable connectors for attachment to a power cord, similar to connectors  6 ,  7  and  8 . 
         [0030]    Both arc sensor  20  and current sensor  30  preferably comprise zero-phase current transformers, each constructed of a conducting wire coil wound around the circumference of an annular core, all encased within an insulated casing. The core may be constructed from an 80% nickel-iron permalloy, exhibiting high magnetic permeability, low coercivity, near zero magnetostriction, an magnetoresistive characteristics. As shown in  FIG. 1 , both the line and neutral conductors of the AC power line to be monitored are passed through a central aperture, or bore, of current sensor  30 , while only the line conductor is passed through a central aperture of arc sensor  20 , before both conductors are coupled to relay  70 . 
         [0031]    Current sensor  30  accordingly operates as a differential sensor, detecting differences in current carried through the line and neutral conductors. The output of current sensor  30 , a voltage indicative of the differential current, is amplified by amplifier  160 . Comparator  170  compares the output of amplifier  160  to a predetermined reference voltage. If the output of amplifier  160  exceeds the reference voltage, comparator  170  outputs an OFF signal  175  to SCR  60 . SCR  60  may comprise, for example, a conventional triac device. SCR  60 , in turn, drives relay  70 , causing it to switch from its normally closed position to its open, latched position. Relay  70  is a double pole single throw (DPST) switch, and SCR  60  accordingly causes both switches of relay  70  to simultaneously open. This, in turn, simultaneously breaks the line conductor connection between prong  2  and connector  7 , and the neutral conductor connection between prong  1  and connector  6 . Relay  60  includes a mechanical latching mechanism which, once the relay is tripped open, maintains the DPST switch in an open, nonconducting orientation until reset switch  90  is manually actuated. Other latching mechanisms, such as a magnetic latch, may alternatively be used. 
         [0032]    Arc sensor  20  responds to high frequency transient current in the line conductor. The output of arc sensor  20  is rectified and then fed to envelope detector  120 , which reshapes the signal, and filters out ripple. The output of envelope detector  120  is amplified by amplifier  130 . Comparator  140  compares the output of amplifier  130  to a predetermined reference voltage. The output of comparator  140  is thus a pulsed digital signal  145  that is indicative of the occurrence of high frequency variations in the line conductor. These high frequency variations are anomalies to the otherwise smooth, sinusoidal voltage of the line conductor. Test switch  100  effectively overrides the output of amplifier  130  and, when manually depressed, forces comparator  140  to output a constantly asserted, rather than a pulsed signal to MCU  150 . This, in turn, is interpreted by MCU  150  as being a request to test the AFCI/LCDI device, causing MCU  150  to emit an OFF signal  175  to SCR  60 . 
         [0033]    As shown in  FIG. 1 , pulsed digital signal  145  is fed to an input port of microcontroller unit (MCU)  150 . MCU  150  may be any suitable microprocessor or microcontroller, preferably with on-chip read-only and random access memory for program and data storage, respectively. MCU  150  operates as an analyzer, continuously analyzing pulsed digital signal  145  for the presence a plurality of characteristics which are indicative of an arcing condition, or an arc fault occurring in the power line that is being monitored by the present AFCI/LCDI apparatus. If MCU  150  determines that an arc fault has occurred, it issues an OFF signal  175  to SCR  60 . 
         [0034]    AFCI/LCDI apparatus  10  is shown in further detail in  FIG. 2 . In  FIG. 2 , resistors and variable resistors are generally depicted using the European and International Electrotechnical Commission symbol convention, rather than the United States and Japanese symbol convention. 
         [0035]    As shown in  FIG. 1 , variable resistor  9  permits the load across the line and neutral conductors to be manually adjusted. Regulator or DC power supply  80  ( FIG. 1 ) is shown as comprising a full wave bridge rectifier, constructed of diodes  81 ,  82 ,  83  and  84 . The output of the DC power supply is Vdd  85 , a 5-volt supply powering, amongst other components, power indicating LED  110 , MCU  150  and operational amplifiers  135 ,  144 ,  163  and  174 . 
         [0036]    Amplifier  160  ( FIG. 1 ) is shown in  FIG. 2  as comprising variable resistor  161 , resistor  162 , operational amplifier  163 , resistor  166  and capacitor  167 . Variable resistor  161  permits fine adjustment of the output of amplifier  160 . Comparator  170  ( FIG. 1 ) is shown in  FIG. 2  as comprising resistors  171 ,  172 ,  173  and operational amplifier  174 . 
         [0037]    Relay  70  ( FIG. 1 ) is shown in  FIG. 2  as comprising solenoid  71 , and switches  72  and  73 , having a common throw. Solenoid  71  contains an armature which is normally in the extended position. When activated, SCR  60  energizes the coil of solenoid  71 , causing a portion of the armature to retract within the coil. This, in turn, opens switches  72  and  72 , causing them to remain latched in an open position until reset switch  90  is manually activated. 
         [0038]    As shown in  FIG. 2 , the output of arc sensor  20  is rectified by diodes  181 ,  182 , and the rectified output is fed to amplifier  130  ( FIG. 1 ), comprising capacitor  131  and  134 , resistors  132  and  133 , and operational amplifier  135 . The output of amplifier  130  is fed to comparator  140  ( FIG. 1 ), comprising resistors  141 ,  142  and  143 , and operational amplifier  144 . Pull-up resistor  102  permits test switch  100  to pull up the reference voltage to comparator  144  at conductor  101 , forcing a constantly asserted digital signal  145  to be input to MCU  150 . 
         [0039]    Crystal  151  and capacitors  152  and  153  establish an appropriate clock frequency for MCU  150 . MCU  150  repeatedly samples digital input  145 , and analyzes the signal for adjacent pulses having characteristics which are considered to be indicative of an arc fault condition in the power line being monitored. When such a condition is deemed to exist by the software or firmware programming executed by MCU  150 , MCU  150  emits OFF signal  175 , which, in turn, causes SCR  60  to trip relay  70 . As a result, relay  70  can be tripped to the open position by either an output of MCU  150 , when an arc fault condition is deemed to exist, or the output of leakage current detection circuitry  50 , when excessive current leakage is detected. 
         [0040]    The top level algorithm  200  executed by the MCU is shown in  FIG. 3 . In step  210 , a power-on condition is detected by the MCU. Next, program initialization  220  is performed, including the clearing of random access memory. MCU may perform an internal self-test at this time. Next, the arc fault analysis function  230  is performed. In step  240 , a test is made to determine if an arc fault was detected by arc fault analysis function  230 , as indicated by a Boolean flag set by the function. If not, branch  241  is taken, and the arc fault analysis function  230  is again performed. If, however, an arc fault was detected by arc fault analysis function  230 , branch  242  is taken. In step  250 , an OFF signal is emitted on an appropriate output pin of the MCU, causing the solenoid to energize and, in turn, causing the relay contacts to transition from the closed, conducting position to the open and latched, nonconducting position. Processing ends in exit step  260 . 
         [0041]    Arc fault analysis function  230  is shown in further detail in  FIG. 4 . Upon function entry  300 , a sample of the pulsed digital signal  145  output from comparator  140  ( FIG. 1 ) is taken by the MCU and stored in internal random access memory, in the form of a “sliding window” of such samples, analogous to a first-in, first-out queue of such samples taken over time. This permits a snapshot of the pulsed digital signal over the immediately prior 125 milliseconds to be reviewed and analyzed by the MCU. 
         [0042]    In step  320 , a test is made to determine if a first criteria indicative of potential electrical arcing in the alternating current power line has occurred. In particular, a test is made to determine if at least four pulses have occurred in the pulsed signals sampled by the MCU over the last 125 milliseconds, indicating at least four anomalous, high frequency events in the otherwise sinusoidal signal of the line conductor. Four pulses is a predetermined threshold quantity of pulses considered to be a criterion which may be indicative of electrical arcing. If not, no arc fault condition is deemed to have occurred, and branch  321  is taken to  370 , where prior arc memory status variables are cleared in preparation for the next round of arc fault analysis. The arc fault analysis function exits in step  380 . 
         [0043]    If at least four pulses have occurred in the last 125 milliseconds, transition  322  is taken to step  330 . In step  330 , a test is performed to determine if a second criteria indicative of potential electrical arcing in the alternating current power line has occurred. In this test, the intervals T 1 , T 2 , T 3  . . . Tn ( FIGS. 6 ,  8 ) between adjacent pulses are added together to form an interval duration summation. If the interval duration summation does not exceed a predetermined threshold of 50 milliseconds, no arc fault condition is deemed to have occurred, and transition  331  is taken to step  370 . 50 milliseconds is a threshold duration value that is considered to be a criterion which may be indicative of electrical arcing. 
         [0044]    Otherwise, two criteria indicative of potential electrical arcing in the alternating current power line are now deemed to have occurred, and transition  332  is taken to step  340 . In step  340 , the individual pulse widths w 1 , w 2 , w 3  . . . wn of all of the pulses sampled over the last 125 milliseconds are compared to each other. If all of the pulses are substantially similar in width, no arc fault condition is deemed to have occurred, and transition  341  is taken to step  370 . 
         [0045]    Otherwise, if all of the pulse widths are substantially different or dissimilar in duration, three criteria indicative of potential electrical arcing in the alternating current power line are now deemed to have occurred, and transition  342  is taken to step  350 . In step  350 , the intervals T 1 , T 2 , T 3  . . . Tn ( FIGS. 6 ,  8 ) between adjacent pulses sampled over the last 125 milliseconds are compared to each other. If all of the pulse intervals are substantially similar to each other, no arc fault condition is deemed to have occurred, and transition  351  is taken to step  370 . 
         [0046]    Otherwise, if the pulse interval times are substantially different or dissimilar, four criteria indicative of potential electrical arcing in the alternating current power line are now deemed to have occurred, and transition  352  is taken to step  360 . Upon all four of the above-identified criteria being met for the same 125 milliseconds of sampled data derived from the arc sensor, an arc fault in the power line is deemed to have occurred. Accordingly, in step  360 , a Boolean variable in random access memory is set, indicating that an arc fault is considered to have occurred in the alternating current power line that is being monitored. Transition is taken to step  380 , where the current iteration of arc fault analysis processing  230  ends. 
         [0047]    Although, in a preferred embodiment, the presence of all four of the above-described criteria are necessary conditions for an arc fault to have occurred, it is also contemplated that a combination of fewer than all four conditions being met may result in an arc fault being deemed to have occurred, such as, for example, any of the individual criterion identified above, any combination of any two of the above-identified criteria, or any combination of any three of the above-identified criteria being met. 
         [0048]    A waveform diagram showing a monitored power line under arcing conditions is shown in  FIG. 5 , with voltage plotted along vertical axis  501  and time plotted along horizontal axis  502 , showing approximately 125 milliseconds of data from vertical axis  501  to reference line  509 . High frequency variations in the normally sinusoidal wave of the AC power line, potentially indicative of the presence of arcing, are shown at positions  503 ,  504 ,  505 ,  506 , and  507 . 
         [0049]    A waveform diagram showing the pulsed digital signals  145  ( FIGS. 1 and 2 ) produced by the arc detection circuitry and output by comparator  140 , corresponding to a monitored AC power line having the characteristics of  FIG. 5  passing through the aperture of arc sensor  20 , is shown in  FIG. 6 , with voltage plotted along vertical axis  601  and time plotted along horizontal axis  602 , showing approximately 125 milliseconds of data from vertical axis  601  to reference line  609 . Referring to  FIGS. 5 and 6 , high frequency variation  503  causes the apparatus to produce a digital signal pulse having a pulse width of w 1 . High frequency variation  504  causes the apparatus to produce a digital signal pulse having a pulse width of w 2 . High frequency variation  505  causes the apparatus to produce a digital signal having a pulse width of w 3 . High frequency variation  506  causes the apparatus to produce a digital signal having a pulse width of w 4 . High frequency variation  507  causes the apparatus to produce a digital signal having a pulse width of wn. In  FIG. 6 , the interval between pulses w 1  and w 2  is designated T 1 . The interval between pulses w 2  and w 3  is designated T 2 . The interval between pulses w 3  and w 4  is designated T 3 . The interval between pulses w 4  and wn is designated Tn. 
         [0050]    In  FIG. 6 , five digital pulses are shown occurring within the 125 millisecond period, or window. The sum of the durations, or pulse widths w 1  through wn of these five digital pulses exceed 50 milliseconds. The pulse widths w 1  through wn are not substantially similar to each other, but are rather substantially dissimilar and non-uniform, with w 3  being the longest duration, w 1  and wn being of lesser duration, and w 2  and w 4  being of still lesser duration. The intervals between pulses T 1  through Tn are also not substantially similar to each other, but are rather substantially dissimilar and non-uniform, with T 3  being the longest interval, t 2  being the next longest, Tn being the next longest, and T 1  being the shortest interval. As can be seen, all four of the criteria indentified above as being indicative of potential electrical arcing in the alternating current power line are all present in the digital waveform of  FIG. 6 . As a result, the MCU, executing the algorithm of  FIGS. 3 and 4  to perform the analysis of the digital pulses derived from the arc sensor, will issue an OFF signal to the SCR, opening the relay and disconnecting the line and neutral conductors of an appliance line cord attached to the terminals of the AFCI/LCDI apparatus from the prongs of the apparatus which, in turn, are plugged into an AC power source. 
         [0051]    A waveform diagram showing a monitored power line displaying high frequency variations, but which is not under actual arcing conditions, is shown in  FIG. 7 . An AC power line may exhibit such high frequency variations when, for example, a dimmer switch is coupled in-line with the AC power source. In  FIG. 7 , voltage is plotted along vertical axis  701  and time is plotted along horizontal axis  702 , showing approximately 125 milliseconds of data from vertical axis  701  to reference line  709 . High frequency variations in the normally sinusoidal wave of the AC power line, which are not in this case indicative of the presence of arcing, are shown at several positions including positions  703 ,  704 ,  705 ,  706 ,  707  and  708 . 
         [0052]    Another waveform diagram showing the pulsed digital signals  145  ( FIGS. 1 and 2 ) produced by the arc detection circuitry and output by comparator  140 , corresponding to a monitored AC power line having the characteristics of  FIG. 7  passing through the aperture of arc sensor  20 , is shown in  FIG. 8 , with voltage plotted along vertical axis  801  and time plotted along horizontal axis  802 , showing approximately 125 milliseconds of data from vertical axis  801  to reference line  809 . Referring to  FIGS. 7 and 8 , high frequency variation  703  causes the apparatus to produce a digital signal pulse having a pulse width w 1 . High frequency variation  704  causes the apparatus to produce a digital signal having a pulse width of w 2 . High frequency variation  705  causes the apparatus to produce a digital signal having a pulse width of w 3 . High frequency variation  706  causes the apparatus to produce a digital signal having a pulse width of w 4 . High frequency variation  707  causes the apparatus to produce a digital signal having a pulse width of wn. High frequency variation  708  causes the apparatus to produce a digital signal having a pulse width of wn+1. In  FIG. 8 , the interval between pulses w 1  and w 2  is designated T 1 . The interval between pulses w 2  and w 3  is designated T 2 . The interval between pulses w 3  and w 4  is designated T 3 . The interval between pulses wn and wn+1 is designated Tn. 
         [0053]    In  FIG. 8 , at least nine digital pulses are shown occurring within the 125 millisecond period, or window, exceeding the predetermined threshold of four pulses. As the duty cycle of the asserted digital signal shown in  FIG. 8  does not exceed 40 percent, the sum of the durations, or pulse widths w 1  through wn+1 of these digital pulses does not exceed the predetermined threshold of 50 milliseconds. The pulse widths w 1  through wn are all substantially uniform and similar to each other. The intervals between pulses T 1  through Tn are also likewise all substantially uniform and substantially similar to each other. As can be seen, all four of the criteria identified above as being indicative of potential electrical arcing in the alternating current power line are not all collectively present in the digital waveform of  FIG. 8 . In particular, only the first of the four criteria have been met. As a result, the MCU, executing the algorithm of  FIGS. 3 and 4  to perform the analysis of the digital pulses derived from the arc sensor, will not issue any OFF signal to the SCR as a result of its analysis of the digital waveform of  FIG. 8 , and the line and neutral conductors of an appliance line cord attached to the terminals of the AFCI/LCDI apparatus will accordingly remain in electrical contact with the prongs of the apparatus and, in turn, with the AC power source, even in the presence of high frequency anomalies in the monitored AC power line, since these high frequency variations are the result of the presence of a dimmer switch in line with the AC power source, and not any arcing of the line cord conductors. The MCU algorithm, and the AFCI/LCDI device, overall, is thus capable of accurately discriminating between high frequency variations and anomalies in the AC power signal which are the result of actual arcing conditions, versus those which are not the result of arcing conditions and, accordingly, which should not result in the triggering of a relay to disconnect a power cord and appliance from an AC power source. 
         [0054]    It will be understood that modifications and variations may be effected without departing from the spirit and scope of the present invention. It will be appreciated that the present disclosure is intended as an exemplification of the invention and is not intended to limit the invention to the specific embodiments illustrated and described. The disclosure is intended to cover, by the appended claims, all such modifications as fall within the scope of the claims.