Abstract: A system and a method of diagnosing a contactor through a sound sensor, which determines whether a contactor is erroneously operated based on a result of sensing a mechanical transition sound generated during an on/off operation of the contactor. The contactor diagnosis may be applied to a battery management system and may further include counting the number of transition operations of the contactor and/or may be used for diagnosing the life of the contactor.

Abstract: An energy metering system includes a plurality of sensors arranged in proximity to circuit breakers of a distribution panel for sensing a magnetic field in the area of the circuit breakers and providing corresponding sensor data. The system further includes a data processing system for converting the sensor data of the plurality of sensors into electrical load information for a plurality of electrical circuits protected by corresponding circuit breakers. The system further includes a calibration unit configured to determine at least a reference voltage and a reference current of at least one circuit. The data processing system is configured to calibrate a relationship between the sensor data and the load information based on the reference voltage and reference current determined by the calibration device in a calibration mode of the energy metering system.

Abstract: A control system for an electrical load, which control system is intended to receive a voltage supplied by a mains electricity supply and includes a control switch, which is designed to take an open state or a closed state, a signalling indicator connected in parallel with the switch and designed to take two different states that are each linked to the open state or the closed state of the switch, a control device connected to the signalling indicator and designed to limit a voltage on the terminals of the electrical load below a threshold value when the switch is in the open state.

Abstract: A generator coupling kit is provided. In exemplary embodiments, the generator coupling kit may comprise a wire adapted to couple with a generator on a first end, the wire adapted to couple with an outdoor box on a second end; the outdoor box adapted to couple with the wire; an indoor electrical panel adapted to couple with the outdoor box via a generator breaker; and the generator breaker adapted to couple with indoor electrical panel, the generator breaker adapted to couple with the outdoor box via internal wiring, the generator breaker comprising a circuit breaker.

Abstract: A method and system is disclosed for monitoring and viewing physical parameters while the emulator is emulating a design. Additionally, the parameters are in real time or substantially real time, such as after a periodic update. In one embodiment, a monitoring portion of the emulator periodically monitors the emulator boards and power supplies for physical information. The physical information is communicated to a workstation for communication to a user. For example, the workstation can display the physical information in a graphical user interface (GUI) that shows which boards are plugged in the system and which slots are empty. In yet another aspect, the user can select a particular board in the system and view communication information, such as data errors, status, link errors, global errors, etc.

Abstract: An electric energy distribution system may include plural loads configured to receive electric energy from a common feed or branch. Each of the loads may be configured to operate in at least first and second modes such that it may consume current, VA or power up to a first cap when running in its first mode and up to a second cap when running in its second mode. The first cap may be higher than the second cap. A sensor component may monitor a parameter that corresponds to an aggregate amount of electric energy being consumed by all of the plural loads from the common feed or branch. A manager component may be configured, when the parameter meets or exceeds the threshold, to select one of the loads currently running in its first mode and to cause the selected load to run in its second mode.

Abstract: A method and system is disclosed for monitoring switchgear. The current supplied to the main bus is measured. The current flowing through a plurality of feeder circuits is also measured. The temperature of the main bus at one or more nodes is measured, wherein a node is a connection point between the main bus and each feeder circuit. The current flowing through one of the nodes is determined by subtracting the current flow through each the feeder circuit upstream from the node, from the current supplied by the input circuit. An alarm condition is determined if the temperature at a node exceeds a predetermined temperature value for a given current flow through the node. The alarm condition is thereafter displayed to a switchgear operator.

Abstract: A fuse box system and method providing for visual and/or remote sensing of interrupted fusing elements is disclosed. The system incorporates LEDs and/or remote sensing apparatus to permit indication of a “blown” fuse and/or circuit protection breaker. This system may be configured for both polarized and/or non-polarized applications and generally provides for indicator illumination when a fuse/breaker is blown. Some preferred embodiments may incorporate current sourcing technologies to permit operation of the system over wide range of system voltages, as well as provisions for wired and/or RF/wireless interrogation of the fuse/breaker status. Alternate embodiments including systems/methods to permit remote sensing of fuse status and/or circuit current monitoring, and may be retrofit within existing fuse/breaker panel systems in some configurations.

Abstract: A motor control center comprises a plurality of bays in which switchgear components, circuit protective components, automation components and power electronic components are disposed for driving motors and other loads. Network optical conductors are routed through one or more wireways adjacent to the bays. Distribution nodes are coupled to the conductors and are interconnected with respective network terminals within the bays. Components within individual bays for which EtherNet and/or Internet connectivity is desired are coupled to the network terminals. The conductors may comprise plastic optical fibers and may be designed to operate in the relatively high voltage environment of the motor control center bays.

Abstract: An electrical circuit tester including a resistive load and a testing station for detecting the variable load. The testing station includes at least one electrical current transducer capable of detecting the variable load in an adjacent electrical power circuit. The detection of the variable load is communicated to the testing station and a variable load detection function.

Abstract: A motive unit, such as a generator, is disclosed. The motive unit has a fault transmitter to provide a status indication of a component of the motive unit. Failure of a component, such as a diode on the rotor of a generator, can be accordingly communicated.

Abstract: A circuit breaker includes an actuator, a switching device connected to the actuator, and a test unit configured to test a connection between the actuator and the switching device by detecting a first connection voltage at the connection between the actuator and the switching device. The test unit is further configured to test the operation of the switching device by turning the switching device on without operating the actuator.

Abstract: A motor control center comprises a plurality of bays in which switchgear components, circuit protective components, automation components and power electronic components are disposed for driving motors and other loads. Network optical conductors are routed through one or more wireways adjacent to the bays. Distribution nodes are coupled to the conductors and are interconnected with respective network terminals within the bays. Components within individual bays for which EtherNet and/or Internet connectivity is desired are coupled to the network terminals. The conductors may comprise plastic optical fibers and may be designed to operate in the relatively high voltage environment of the motor control center bays.

Abstract: Monitoring assemblies for determining an operational state of a circuit protector in an electrical circuit.

Abstract: A wireless electrically isolated plug-n-play communications system for branch circuit breakers. The system providing means for automatically connecting the wireless electrically isolated communication system between the branch circuit breaker and a communications strip as the branch circuit breaker is being installed in the load center.

Abstract: A system includes a number of electrical switching apparatus having separable contacts, an operating mechanism structured to open and close the separable contacts, a trip mechanism cooperating with the operating mechanism to trip open the separable contacts, a test circuit structured to test the trip mechanism and determine a failure to protect condition thereof, and a communication circuit structured to communicate the failure to protect condition. The system also includes an electrical distribution panel having a housing housing the number of electrical switching apparatus, and a communication interface structured to receive the failure to protect condition from the communication circuit and annunciate the failure to protect condition.

Abstract: A power supply device for supplying power to a communication device includes a power source, a first fuse, a second fuse, a voltage converter, a photo coupler, and a central processing unit (CPU). The voltage converter is configured for receiving first power signals from the power source via the first fuse and the second fuse, and converting the first power signals to second power signals. The photo coupler connected in parallel to the third resistor, configured for outputting a first electrical signal upon the condition that the first fuse and the second fuse are operational, and outputting a second electrical signal upon the condition that at least one of the first fuse and the second fuse is blown. The CPU is connected to the photo coupler, configured for generating an alarm message upon receiving the second electrical signal from the photo coupler.

Abstract: A user interface for a wireless device used to monitor multiple groups of faulted circuit indicators. Each group of faulted circuit indicators includes a radio interface unit, which is coupled to each of the faulted circuit indicators in the group. The user interface includes an identification indicator, which includes a plurality of radio interface unit status indicators, each of which corresponds to a particular radio interface unit, and which indicates a selected radio interface unit. The user interface also includes a way indicator comprising a plurality of faulted circuit indicator status indicators, each of which corresponds to a particular faulted circuit indicator coupled to the selected radio interface unit. In addition, each radio interface unit status indicator indicates whether a particular radio interface unit coupled to a faulted circuit indicator is asserting a fault condition.

Abstract: A system includes a number of electrical switching apparatus having separable contacts, an operating mechanism structured to open and close the separable contacts, a trip mechanism cooperating with the operating mechanism to trip open the separable contacts, a test circuit structured to test the trip mechanism and determine a failure to protect condition thereof, and a communication circuit structured to communicate the failure to protect condition. The system also includes an electrical distribution panel having a housing housing the number of electrical switching apparatus, and a communication interface structured to receive the failure to protect condition from the communication circuit and annunciate the failure to protect condition.

Abstract: A circuit breaker includes separable contacts, an operating mechanism opening and closing the contacts, a first processor determining an open or closed state of the contacts, and a wireless transceiver transmitting the open or closed state from the first processor and receiving a signal. A first accessory includes a wireless receiver, a second processor and outputs. A second accessory includes a wireless transmitter, a third processor and a circuit generating the signal for or communicating the signal to the third processor, which outputs the signal to the wireless transmitter, which transmits the signal to the wireless transceiver. The first processor receives the signal from the wireless transceiver and causes the mechanism to open or close the contacts. The wireless receiver receives the open or closed state from the wireless transceiver. The second processor receives the open or closed state from the wireless receiver and outputs the same to the outputs.

Abstract: Presented is a communications protocol for use by interconnected hazardous condition detectors, such as smoke and carbon monoxide detectors for use in dwellings and other structures. This communications protocol provides conventional signaling to indicate the presence of a smoke condition necessitating the generation of a smoke temporal pattern by all interconnected detectors. The protocol further defines a signaling method by which conventional smoke detectors that are incapable of providing temporal patterns other than that required for a smoke alarm condition will not be sent into an alarm mode of operation upon receipt of a signal other than the conventional smoke alarm signal. This communications protocol defines a pulsed signal to indicate a non-smoke alarm condition that is of a duration that will not trigger the conventional smoke alarms.

Abstract: A control apparatus for a plurality of devices, especially circuit breakers. The control apparatus includes activation circuitry for each device, and a power supply for supplying electrical power to the activation circuitry. The control apparatus adds a respective electrical signature component to the supplied electrical power upon detection that a respective device has operated. The signature components allow analysis equipment to determine which device has operated by analysing the supplied electrical power.

Abstract: The programmable panel schedule is an apparatus for monitoring and modifying electrical circuits. The programmable panel schedule can eliminate the need to rely on paper schedules and permit a building engineer to instantly assess any monitored circuit for changes, additional capacity and usage history.

Abstract: A power protection system for protection against an electrical transient surge and/or interference. Such a system can be useful in the dispensing of fuel at gas stations, convenience stores, truck stops, and other such locations, for protection of the low voltage signal wires that go from the dispenser to the store. Broadly contemplated are modular arrangements where removal of a corrupted module in a cabinet containing several modules will still keep the general communications circuit intact. Particularly contemplated are modules which include integral fuses and indicator lights.

Abstract: A control system includes an enclosure, a control panel, and a plurality of controls, indicators, or both mounted on the control panel or in the enclosure. At least some of the plurality of controls, indicators, or both are configured to wirelessly communicate with each other inside the enclosure, and at least some controls including wirelessly controlled relays are configured to control devices outside the enclosure. Also, the wirelessly configured controls, indicators, or both are further configured to communicate with a plurality of other controls, indicators, or both in the control system.

Abstract: A method to identify a person driving a vehicle and his/hers driving style, and also to switch on the vehicle either to a driving-allowing mode or to a drive-stop mode, is provided. In the method, the vehicle includes a scanner, and the driver is provided with a data-containing card or object. According to the method, the driving style information of the driver is stored on the card or object, and on starting driving the driver inserts the card or object into the vehicle scanner. Thereafter, data received from selected vehicle controls and/or data from varying information-collecting detectors is compared with information stored on the driver's driving style card, and on basis of the comparison the control unit in the vehicle either allows driving or enters a drive-stop mode.

Abstract: A digital signal path selector is disclosed in its simplest form for selectively connecting two input terminals to two output terminals. Both input terminals and output terminals are laid out on a control panel, on which there are also provided two input select pushbuttons, positioned one adjacent each input terminal, and two output select pushbuttons positioned one adjacent each output terminal. The input select pushbuttons and the output select pushbuttons are arranged so close to one another that any one input select pushbutton and any one output select pushbutton are capable of concurrent depression with the thumb and forefinger of one hand in order to specify one associated input terminal and one associated output terminal for creation of a signal path therebetween.

Abstract: A power distribution panel with a chassis defining an interior with a first opening and a second opposing opening. The panel including a module with a bottom, a first face and a second face, and including a power input terminal, a plurality of power output terminals, and an electrical circuit connecting each power output terminal to the power input terminal, each circuit including a circuit protection device. The power input terminal, the power output terminals and the circuit protection devices are mounted to one of the first or second faces. The module is configured to be received through the first opening and removably mounted within the interior so that the power input terminal, the power output terminals and the circuit protection devices are accessible through one of the first and second openings when the module is mounted within the chassis. A module including power distribution components and circuitry adapted to be removably mounted within a power distribution panel chassis.

Abstract: Presented is a communications protocol for use by interconnected hazardous condition detectors, such as smoke and carbon monoxide detectors for use in dwellings and other structures. This communications protocol provides conventional signaling to indicate the presence of a smoke condition necessitating the generation of a smoke temporal pattern by all interconnected detectors. The protocol further defines a signaling method by which conventional smoke detectors that are incapable of providing temporal patterns other than that required for a smoke alarm condition will not be sent into an alarm mode of operation upon receipt of a signal other than the conventional smoke alarm signal. This communications protocol defines a pulsed signal to indicate a non-smoke alarm condition that is of a duration that will not trigger the conventional smoke alarms.

Abstract: An electrical safety monitor (20) includes a housing (50) with a display face (70) and a securing section (54) that connects with an electrical panel (62). Electrical circuitry (30) is contained in the housing (50). The electrical circuitry (30) communicates with electrical lines (L1, L2, L3, GND) of the panel (62), and defines high impedance electrical paths between pairs of electrical lines (L1, L2, L3, GND). Each high impedance path includes a positive light emitting diode (D1, D2, D3, D4) arranged to draw current from a line carrying a positive electrical energy potential and a negative light emitting diode (D5, D6, D7, D8) arranged to draw current from a line carrying a negative electrical energy potential relative to the positive electrical energy potential. The positive and negative light emitting diodes are disposed on the display face (70) of the housing (50). Each light emitting diode produces light responsive to current flow in a high impedance path that includes the light emitting diode.

Abstract: A fused disconnect switch assembly includes a pull out fuse assembly and a switch housing assembly. The fuse assembly includes a line side conducting portion, a load side conducting portion, and a fuse element therebetween. The switch housing assembly includes a fuse receptacle for receiving the fuse, a first contact assembly coupled to the line side conducting portion of the fuse and a second contact assembly coupled to the load side conducting portion of the fuse when the fuse is inserted into the receptacle. An open fuse indication device is in communication with conducting portions of the fuse, and an alarm terminal output extends from the switch assembly housing and is in communication with the open fuse indication device. The open fuse indication device provides local fuse state indication and the alarm terminal output facilitates remote fuse state indication when coupled to external circuitry.

Abstract: The present invention provides an improved fused disconnect. More specifically, the present invention provides a fusible disconnect that includes a single line side terminal, two independent load side terminals, two independent removable fuse carriers and two independent blown fuse indicators. The common line side terminal provides power to both of the removable fuse carriers. The present invention therefore enables a single, standard sized disconnect to isolate and provide overload protection for two electrical load devices, thus reducing the required number of fused disconnects by one half. The present invention also reduces the required number of line side connections by one half. To this end, in an embodiment of the present invention, a multiple pole fused disconnect includes a housing, a line terminal secured to the housing and a plurality of load terminals secured to the housing.

Abstract: The present invention provides an improved fused disconnect. More specifically, the present invention provides a fusible disconnect that includes a single line side terminal, two independent load side terminals, two independent removable fuse carriers and two independent blown fuse indicators. The common line side terminal provides power to both of the removable fuse carriers. The present invention therefore enables a single, standard sized disconnect to isolate and provide overload protection for two electrical load devices, thus reducing the required number of fused disconnects by one half. The present invention also reduces the required number of line side connections by one half. To this end, in an embodiment of the present invention, a multiple pole fused disconnect includes a housing, a line terminal secured to the housing and a plurality of load terminals secured to the housing.

Abstract: A protective relay, system, and relay operation method which allows logic functions to be distributed amongst multiple protective relays associated with a power distribution system. The protective relays include communications ports for exchanging messages over a peer-to-peer communications network, and include programmable logic. Each protective relay receives logic operands contained in the messages from remote protective relays, executes logic equations using the received operands, provides protective control if needed, and outputs operands to other protective relays.

Abstract: A semiconductor apparatus, including an intelligent power module, facilitates preventing sudden stop of an inverter due to an anomaly from affecting a factory operation adversely. When an anomaly occurs in IGBTs of the inverter, one of protection circuits outputs an alarm signal via an alarm enable line. In advance to the alarm signal, when the protection circuit detects a sign of a possible anomaly from a collector current or a chip temperature of any of the IGBTs exceeding a second predetermined collector current level or a second predetermined temperature level higher than the normal collector current value or the normal chip temperature but lower than a first predetermined collector current level or a first predetermined temperature level for outputting the alarm signal, the protection circuit outputs a preliminary alarm signal via a preliminary alarm line without turning off the pertinent IGBT.

Abstract: A fuse extractor and puller including a generally cylindrical fuse receiving portion, a lifting and inserting tower attached to the cylindrical fuse receiving portion, and a gripping head attached to the tower and having specially molded characters etched thereon. The tower portion of the fuse puller is hollow and incorporates a continuity detector having an indicator for indicating the condition of a fuse comprising a light extending through the top of the gripping portion, and first and second spring contacts attached to the continuity detector, adapted to contact the electrical terminals of a fuse positioned within the puller. The tower further includes a cantilevered support for supporting the continuity detector so that the light may be pressed downwardly against the gripping portion and the stress created thereby is absorbed, preventing damage to the light.

Abstract: A blown fuse commutator strip which is removably attachable to a pre existing plug-in type fuse, with the commutator strip having an indicator thereon which will notify the user that the fuse has blown and needs replacing.

Abstract: An apparatus and method for distributing power includes a housing, at least one input terminal, and at least one output terminal. The input and output terminals are each positioned in the housing. The input terminal is operatively connected to the output terminal. At least one circuit breaker is positioned in the housing. The circuit breaker includes an on position and an off position. The circuit breaker is operatively connected to the input terminal and the output terminal. An alarm circuit is operatively connected to the output terminal to prevent an alarm signal when an electronic chassis is not operatively connected to the output terminal and the circuit breaker is in the off position.

Abstract: Provided is a modular precharge circuit capable of rapidly recharging an equipment circuit path prior to insertion of a modular fuse or modular circuit breaker. The precharge circuit includes a switch to begin the operation of precharging, and a charge indicator to indicate appropriate charging has occurred. Charging occurs through use of a resistive network which receives an inrush current due to capacitance in the equipment circuit path. Once an equipment circuit path has been precharged to a desired level, a charge indicator signifies such charging is complete and the precharged unit is removed whereafter an appropriate fuse module and/or circuit breaker module is inserted. The precharge circuit further includes a fusing element and an alarm indicator wherein when the circuit enters a fault state such that the fuse is open, the alarm indicator signifies such a situation.

Abstract: There is disclosed a multi-phase fuse status indicator having a green "good" and a red "bad" indicator LED for each line fuse of the respective phases, the current to the LED's being pulsed to cause them to provide a blinking indication. Power used for the logic circuit for the LED's and the LED's themselves and the related heat dissipation is less than 10 watts and is supplied from the power lines connected through the fuses regardless of the fuses' condition. Only two simple conductor connections are required from the fuse status indicator to each fused line of the multi-phase power system.

Abstract: For use within an electrical distribution to control current paths through a plurality of associated circuit breakers, a circuit arrangement comprises a plurality of circuit breakers, each having a status related to open contact position and a closed contact position. An informational display is included within the load-center to display the plurality of statuses at a user access side of the display, and a control circuit, coupled to the circuit breakers and the informational display, automatically monitors the contact status of the circuit breakers and drives the informational display so that a display of the statuses is provided.

Abstract: An electrical distribution system having a load center for programmably and remotely controlling a plurality of circuit breakers, an expander unit coupled to the load center and a plurality of external switches for providing signals to the load center representative of the status of the switches. The load center contains a control module that continually receives inputs from the expander unit via an interface module. It also contains a keyboard and display for programming instructions for closing and opening the individual circuit breakers and for displaying the status of the circuit breakers. The interface module, coupled to the control module, causes the circuit breakers to open and close according to programmed instructions received from the control module or another external device. The expander unit contains a plurality of input circuits coupled to external switches.

Abstract: The present invention provides a circuit breaker control arrangement that is reliable, accurate and cost-effective to manufacture, install and maintain. This circuit breaker arrangement also provides increased modularity by alleviating the need for installing wires to connect each circuit breaker with the control station. The present invention uses circuit breakers that contain internal control technology for interrupting and establishing an associated current path. At least one coded signal designates each circuit breaker, and a communication bus carries these coded signals to each circuit breaker. Decoding technology located on each circuit breaker determines whether the coded signal corresponds to that circuit breaker. If the coded signal does correspond to that circuit breaker, then the decoding technology responds by sending the appropriate response signal over the communication bus, and the circuit breaker's internal control technology either interrupts or establishes the associated current path.

Abstract: A monitoring apparatus includes sensors for interconnection with the load output terminal of a corresponding circuit breaker. The sensors sense the closed and open states of the corresponding circuit breakers and produce closure signals at outputs. The sensor outputs are interconnected in series to produce a combined closure signal for all of the circuit breakers. An indicating circuit interconnected with the combined closure signal outputs a signal, such as a relay contact or an audible, visual, or digital signal, to indicate the combined closure status of the circuit breakers.

Abstract: A fuse box is provided with LED's interconnected with all fuses carried by the fuse box for identifying a blown fuse. The LED's are interconnected with the fuses between the positive (current in) input and ground. When a fuse is blown, the fuse results in an open circuit and the flow of electricity is rerouted through the LED to illuminate the LED. Also provided is a liner which fits over an existing fuse box and includes receptacles for fuses with corresponding LEDs associated with each receptacle for indicating a blown fuse. Also provided are individual liners for individual fuses. The individual liner is sized and configured to accept a fuse therein on a first side, and to extend into a fuse box on a second side thereof. The individual liner includes a LED interconnected therewith for indicating a blown fuse. Also provided is a remote indicator having a plurality of indicators positioned away from a fuse box. Additionally provided is a remote fuse box.

Abstract: A fuse protection and fuse blowing circuit includes a fuse register which has an additional fuse with respect to other fuse registers used in the system. The additional fuse has an output which indicates a blown/not blown state of the additional fuse, and that output is fed back to a blow enable input of each of the other fuses in the fuse register and the other fuse registers. When the additional fuse is set to the blown state, none of the other fuses are allowed to be blown, thereby protecting the device against any accidental blowing of fuses.

Abstract: A power outlet box with special protection logic including a circuit having an on-off switch connected to the power input lead and a first fuse of relatively high rating protecting a first electrical outlet. A number of serially arranged outlets are connected to the power input lead through a selector switch which connects to one of a plurality of fusible links having lower ratings than the first fuse. The capacity of the outlets is controlled by the rating of the fuse selected.

Abstract: An electrically powered annunciating system, for use in electrical panel boxes, having a sensing circuit including a first acoustical transducer to transmit a sonic signal to an annunciating circuit having a second acoustical transducer at a spaced distance from the first transducer to operate the annunciating circuit responsive to a sonic signal received from the first transducer. The sensing circuit powers the first acoustical transducer to produce a sonic signal responsive to a sensed electrical event such as termination of power to an electrical component. The annunciating circuit includes a tuned amplifier for signal purification and amplification, a time delay integrator to prevent accidental circuit operation caused by noise and an annunciator and a communication interface activated responsive to a sonic signal received by the second transducer.

Abstract: Apparatus for generating alarms for a group of circuit interrupters, especially those which respond to arcing faults, includes a device associated with each circuit interrupter providing an indication of a tripped condition and a common alarm generator which generates an alarm when any one, or at least any one of a number of selected circuit interrupters, is in the tripped condition. In one embodiment of the invention, switches indicating that associated circuit interrupters are tripped generate auxiliary trip signals on a common alarm bus. The auxiliary trip signals are latched by a latch on the common alarm bus which energizes a relay to activate a local and/or remote alarm. The latch is reset by a switch on the load center door. In another embodiment of the invention, an IR beam is blocked from reaching a photo-detector whenever a circuit interrupter handle is in the tripped position which also results in energization of a relay to actuate the common alarm.

Abstract: A status indicator for monitoring a fuse or a circuit breaker, including optically isolated triggering and alarm circuits which can be integrated into a fuse holder or circuit breaker housing. More particularly, a status indicator having an LED connected in series with a fuse or circuit breaker across a power source, and a phototransistor arrangement, connected across the power source, in series with an alarm circuit. The arrangement is configured so that as long as current flows through the fuse or circuit breaker, the LED produces light which causes the phototransistor to be maintained in a non-conducting state, and the status indicator to remain in a non-alarm state. Upon failure of the fuse or circuit breaker, current flow to the LED is interrupted, resulting in the phototransistor being biased into a conductive state, and the alarm circuit being activated.