Abstract: A high impedance fault isolation system for a radially connected three phase electric power line that utilizes three phase current measurements to determine the presence of a fault without the need for any voltage measurements or a battery powered controller. This eliminates the need for costly phase voltage measuring devices conventionally required to detect high impedance faults, which makes it economical to install fault isolation system at a greater number of locations throughout the power system. The system detects faults using current measurements by computing the negative and zero sequence current components and comparing the amplitudes of the negative and zero sequence components. A fault is detected when the ratio of the amplitudes of the negative and zero sequence components falls within a predefined fault detection range, such as the range from 0.5 to 1.5.

Abstract: A hub for use with a circuit protection system includes a first input port configured to communicatively couple to at least one sensor device, wherein the at least one sensor device includes a light source and at least one light sensor. The hub also includes a first output port configured to communicatively couple to at least one controller, and a processor communicatively coupled to the first input port and to the first output port. The processor is configured to receive a sensor status signal from the at least one light sensor via the first input port in response to a test pulse emitted by the light source, and transmit a hub status signal to the at least one controller via the first output port based at least in part on the sensor status signal.

Abstract: An apparatus and method for providing ground fault protection to a lifting device utilizing an electromagnet and powered by a generator. The apparatus and method rectifies an AC voltage emanating from the generator source and monitors unsafe operating conditions of the generator's circuit wherein operation of the lifting device is ceased when predetermined electrical operating parameters are exceeded.

Abstract: An apparatus, method, and system for providing ground fault circuit interrupter (GFCI)-type functionality for electrical systems that may experience leakage current, such as those used in outdoor sports lighting applications, and may benefit from mitigation of electrical shock hazards. The resulting system is such that an equipment-grounded electrical system, where the grounding system is actively monitored, in conjunction with the envisioned GFCI functionality, may comprise an electrical protection system whereby personal injury is minimized.

Abstract: A solid state power controller (SSPC) for detecting a parallel arc fault in a direct current (DC) power distribution system includes an input, the input being connected to a DC power source; a power switch connected to the input; an output connected to the power switch, the output being connected to a DC motor controller and associated capacitive load; an output current sensor; an output voltage sensor; and an SSPC controller, the SSPC controller being configured to determine the presence of a parallel arc fault in the DC power distribution system and control the power switch via a gate drive based on inputs from the output current sensor and the output voltage sensor.

Abstract: A residual-current circuit breaker includes a summation current transformer having a core, a first secondary winding wound onto the core, and at least one second secondary winding wound onto the core, with lines of an electric network to be protected extending through the core. A tripping apparatus is operably connected to break contacts for opening the break contacts. A first arrangement is provided for detecting alternating residual currents and connected to the first secondary winding of the summation transformer. A second arrangement is connected to the second secondary winding for detecting direct residual currents, wherein a predeterminable alternating operation of the first and second arrangements is controlled by a timer device.

Abstract: Methods and apparatus to minimize saturation in a ground fault detection device are disclosed. An example method includes connecting a capacitor simulator to a node of the ground fault detector device to prevent saturation, and monitoring power-line conductors for ground fault conditions with the ground fault detector device. An example apparatus to simulate a saturation capacitance in a ground fault device includes a sense coil induced by power-line conductors, and at least one of an amplifier or a current detector including an input connected to the sense coil and an output connected to a ground fault detector. The example apparatus also includes a saturation capacitor simulator connected to a node of at least one of the amplifier or the current detector to prevent saturation.

Abstract: A ground-fault circuit-interrupter (GFCI) system is provided that provides reliable and timely tripping of faulted circuits while minimizing so-called “nuisance” tripping. The GFCI includes a voltage unbalance detection device coupled to the main bus circuit for detecting a voltage unbalance during a fault condition. A computer processor in communication with the voltage unbalance detection device is programmed to determine when an actual fault condition exists based on a state of the voltage unbalance and certain predetermined among the fault signal generated by a GFCI unit in the main bus circuit and the fault signals generated by GFCI units in individual feeder circuits.

Abstract: Current differential protection with charging current compensation is provided for a power apparatus, such as a power transmission line. Individual terminals dynamically determine their respective contributions, if any, to the charging current compensation value as availability of one or more voltage sources dynamically changes within the power apparatus. Respective terminals calculate local contributions to a charging current compensation value based on local voltage measurements. A loss of a voltage source is handled by adjusting multipliers for the remaining compensation points to reflect the total charging current. A local contribution is suppressed when the local voltage source is no longer available. After applying the local contributions, an alpha plane analysis may be used to determine when to trip the power apparatus.

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: An automotive vehicle includes a charge port integrated with the vehicle. The charge port includes electrical contacts configured to receive electrical power from an electric grid, and a fault interrupt circuit electrically connected with the electrical contacts.

Abstract: A current sensor assembly used for detecting ground faults, which includes an enclosure surrounding the current sensor for focusing the magnetic flux produced by conductors passing through the current sensor assembly away from the conductors, thereby reducing load-shift error and producing more accurate current readings for ground-fault sensing. The enclosure has two half members that are secured together to form a toroid-shaped shell that surrounds a toroidal core of the current sensor. A secondary winding and an optional test winding is wound around the toroidal core, and the ends of these windings exit one or more apertures formed in the enclosure. The half members have rounded profiles where the flat surfaces transition into different planes so that the magnetic flux does not encounter any sharp edges or transitions inside the enclosure as the flux flows away from the conductors.

Abstract: A direct current arc fault circuit interrupter includes separable contacts and a trip circuit to trip open the contacts. The trip circuit includes a number of alternating current sensors structured to sense a current flowing through the separable contacts, a number of filter circuits cooperating with the AC current sensors to output a number of AC signals, a number of peak detectors cooperating with the filter circuits to output a number of peak current signals, and a processor cooperating with at least the peak detectors. The processor inputs the number of peak current signals as a plurality of peak current signals or inputs the number of peak current signals and determines the plurality of peak current signals. The processor also determines if the peak current signals exceed corresponding predetermined thresholds for a predetermined time, and responsively causes the contacts to trip open.

Abstract: A leakage current protection plug includes a plug housing, a power supply cord, two copper legs embedded within the plug housing, a leakage current protection device composed of two main moving contacts. A reset button presses the moving contacts to contact the two copper legs, a winding assemble, an iron core, a circuit board assemble, an ZCT. Ends of moving contacts are arranged with contacts that conduct individually with the two copper legs upon coming into contact; the power supply cord, through the ZCT, is connected with the moving contacts; the output of the ZCT is connected with the input of the amplification circuit on the circuit board, while the output of the amplification circuit is connected with the winding assemble.

Abstract: A composite electric circuit breaker, and method thereof, is configured to detect signals regarding arc faults, overcurrent, and earth leakage. Arcs and electric currents are detected by a current transformer and earth leakage is detected by a zero phase current transformer. A variation of electric current, the number of arcs which are generated per a unit time, a present electric current value, and electric current earth leakage are combined to judge whether arc faults occur to then interrupt an electric power supply. Temperature is measured on a printed circuit board, and if temperature rise occurs, the electric power supply is interrupted, and an interruption cause is displayed. Electric accidents and occurrence of fires are prevented simultaneously and more accurately. The interruption causes can be confirmed, analyzed and externally monitored through a network, to thus maximize efficiency of electric management.

Abstract: Dynamic grounding including monitoring the floating DC outputs of a power amplifier, detecting an imbalance in the floating DC outputs, generating a compensation signal in response to a detected imbalance, and adjusting the power amplifier to re-balance the floating DC outputs and suppress transients.

Abstract: A circuit breaker apparatus may be used to interrupt overcurrent and ground fault in a circuit. The circuit breaker apparatus may include an overcurrent coil for tripping the circuit breaker apparatus, a voltage coil also for tripping the circuit breaker apparatus located proximate to the overcurrent coil, ground fault electronics connected to the voltage coil and structured to detect a ground fault in the circuit when the ground fault exceeds a threshold level, and a solid state switch. The ground fault electronics can be structured to send a trip signal to close the solid state switch when a ground fault is detected, the solid state switch is configured to force a current through the voltage coil when the solid state switch is closed, the current being of sufficient magnitude to trip the circuit breaker apparatus.

Abstract: A residual current device for an AC electricity supply comprises a housing (10) and a first load conductor (L) inside the housing connected in series between the supply and a load and including a set of contacts (18) by which an electrical connection between the supply and the load may be made or broken. A current transformer is disposed inside the housing and has a toroidal core (TI) the first load conductor passing through the core and forming one primary winding of the current transformer. At least one further load conductor (N) outside the housing passes through the core (T) via an opening (32) in the housing and forms a further primary winding of the current transformer. A secondary winding (W) on the core produces an output in response to a residual current, and a circuit (RCC) inside the housing is responsive to the output on the secondary winding to open the contacts if the residual current is above a predetermined level.

Abstract: A protective device is disclosed having a circuit breaker for an electrical connection between a transformer and a load, wherein an overcurrent device is arranged between the transformer and the load. The overcurrent device has first magnetoelectric transducers arranged at each phase conductor and the neutral conductor, wherein the overcurrent device uses the transducer currents to in each case establish the presence of a first ground-fault current, and wherein the circuit breaker has a switching device, which interrupts at least the phase conductors between the transformer and the load in the event of the presence of a first ground-fault current (unrestricted earth fault).

Abstract: There is disclosed a circuit interrupting device with symmetrical inputs comprising a first input configured for connection to a power source or a load circuit and a second input configured for connection to a power source. There are a plurality of electrical conductors extending from the first and second inputs and a third input configured for connection to a load provided by a user. There is also a first set of transformers comprising at least one differential transformer and at least one neutral transformer connected to detect leakage current in a load circuit coupled to the first set of terminals. There is also a second set of transformers comprising at least one additional differential transformer and at least one additional neutral transformer connected to detect leakage current in a load circuit coupled to the second set of terminals.

Abstract: Fault detection and interruption in connection with photovoltaic technologies are disclosed. An exemplary apparatus for interrupting a photovoltaic energy conversion system that employs a bipolar photovoltaic array includes a fault detector and interrupter configured to be coupled to the first and the second rails of the photovoltaic array, the fault detector and interrupter configured to detect a condition that requires interruption of the photovoltaic energy conversion system and open a PV tie to uncouple two PV arrays of the bipolar photovoltaic array, thereby decoupling the two PV arrays; and a controller configured to, after the PV tie is opened, open a plurality of main DC contactors thereby decoupling the bipolar photovoltaic array from a remainder portion of the energy conversion system.

Abstract: The present invention is directed to a protective wiring device for use in an electrical distribution system. The device includes a plurality of line terminals and a plurality of load terminals configured to be coupled to the plurality of line terminals in a reset state. A detector circuit is coupled to the plurality of line terminals. The detector circuit is configured to generate a detection signal in response to detecting at least one predefined perturbation in the electrical distribution system. A circuit interrupter assembly is coupled between the plurality of line terminals and the plurality of load terminals. The circuit interrupter assembly is configured to decouple the plurality of line terminals from the plurality of load terminals in response to the detection signal. An end-of-life mechanism is coupled to the detector circuit. The end-of-life mechanism is configured to permanently decouple the plurality of line terminals from the plurality of load terminals in the absence of an intervening signal.

Abstract: An apparatus for ground fault current interrupter with overall end-of-life indication and shutdown protection function includes a first silicon-controlled rectifier, a reverse unit, a test switch unit and a ground fault current interrupter. The ground fault current interrupter includes a second silicon-controlled rectifier, a switch unit, a switch control unit and a rectifier filter unit. When a test current leakage signal is generated, a drive power is provided to the reverse unit, and the input power supply generates a current leakage phenomenon. If the ground fault current interrupter fails, then the second silicon-controlled rectifier will not be triggered, which makes the reverse unit trigger the first silicon-controlled rectifier, such that the rectifier filter unit outputs a DC power flowing through the first silicon-controlled rectifier to interrupt a power supply of the switch control unit.

Abstract: A circuit is disclosed for disconnecting a power source upon the detection of a leakage current comprising a power cable having an insulated first and a second wire. The power cable has a conductive shield surrounding the first and second wires with a drain wire electrically contacting the conductive shield. A disconnect switch is interposed between the power source and the power cable. A primary circuit controls the disconnect switch. A secondary circuit is connected to the drain wire for sensing a leakage current between the conductive shield and one of the first and second wires. An optical switch interconnects the primary circuit and the secondary circuit for opening the disconnect switch upon the secondary circuit sensing a leakage current.

Abstract: An apparatus to detect arc is presented. The apparatus includes a fiber sensor to detect characteristics of an arc flash and a processor to process at least two characteristics of the arc flash. The processor is further configured to generate an arc fault signal. A protective device is configured to mitigate the arc flash based on the arc fault signal.

Abstract: A ground fault interrupter to be used by utility company while effecting repairs to the electrical service for a building is positioned to interrupt the power supply to the building in case of a detected ground fault and utilizes a sensor for detecting the fault current at the service entrance to a building; a contact switch, selectively movable between open and closed positions, mounted for temporary use in series with said power supply to the building; and a microprocessor based circuit for measuring and evaluating fault current detected by the sensor and controlling the selective movement of the contact switch between its open and closed positions.

Abstract: A power supply system for use with a component comprises at least three phases of power supply, with each of said three phases passing through a solid state power controller having an on/off switch. Each of the phases of power pass through a current sense transformer. A ground fault circuit receives an outlet from the current sense transformer. The ground fault circuit includes an analog filter connected into a digital processor. An output of the digital processor is operable to control the switches on the solid state power controllers. The three phases distribute power to the component when the switch on their associated solid state power converter is on.

Abstract: A switching circuit, e.g. an RCD, comprises a pair of mechanical contacts (M) in an alternating current electricity supply (N, L) and circuit means (SCR) for opening the contacts to cut off the supply in response to a switching signal (S). The switching circuit includes further circuit means (Rs, Cs, D2, D3, Q1, Q2) for defining successive periods of time (“activation windows”) during which the magnitude of the supply voltage is not at a maximum and allowing the contacts to open in response to a switching signal only during such windows.

Abstract: A leak current breaker is provided which includes a detector (10) to detect a leakage current from electric lines, a first removing unit (12) to convert the detected leakage current into a voltage and a voltage detector (14) to detect a voltage developed in electric lines A under testing, a second removing unit (16) to remove a harmonic component included in the voltage, a phase contrast detector (20) to detect a phase contrast from a signal waveform having the harmonic component removed, a frequency calculator (21) to calculate a frequency occurring on electric lines A on the basis of the signal waveform of the voltage having the harmonic component removed by the second removing unit (16), a phase angle calculator (22) to calculate a phase angle of the leakage current flowing through the electric lines A on the basis of the phase contrast and frequency, a root-mean-square value calculator (24) to calculate a root-mean-square value of the voltage having the harmonic component removed by the first removing uni

Abstract: Resettable circuit interrupting devices using a center latch are provided. The circuit interrupting devices include those with a reset lockout, reverse wiring protection, and/or an independent trip portion.

Abstract: Disclosed herein is a ground fault protection circuit for an electrical distribution system, the electrical distribution system having a plurality of power sources each having an associated main circuit breaker and being electrically coupled to an associated load with a tie circuit breaker electrically coupled therebetween, the main and tie circuit breakers having associated therewith phase and neutral current transformers (CTs) for sensing an associated current. The ground fault protection circuit includes first, second and third auxiliary differential current transformers, each in signal communication with outputs of respective phase and neutral current transformers associated with respective first and second main circuit breakers and a tie circuit breaker. A control circuit has a defined topology that provides signal communication between each of the auxiliary differential current transformers.

Abstract: An ungrounded or floating DC electrical power distribution system may experience a single line to ground fault. Such a fault may not disrupt operation of the system, but its presence may raise a risk of additional problems if left uncorrected. A system for progressively grounding the ungrounded system may be initiated when a line to ground fault is suspected based on the voltage difference measured to a common chassis point. As grounding through successively lower impedance proceeds, fault current may increase and detection of severity of the line to ground fault may be more readily achieved, thus facilitating localization of the fault. Localization may be achieved through an analysis of direction of capacitive currents in isolatable zones of the system.

Abstract: A differential protection device comprising: differential current measuring means, processing means connected to the measuring means and comprising operating rating selection means and time delay selection means to select tripping curves, actuating means, and test means connected to the measuring means. In the protection device the test means are associated with the operating rating selection means and with the time delay selection means to select a minimum or reduced operating rating and to select a minimum or reduced time delay when said test means are actuated.

Abstract: An exemplary ground fault detection device is capable of detecting a ground fault on multiple phases. The ground fault detection device includes a monitoring module that monitors the phases and determines if there is a non-zero electrical energy value sum for a selected interval on each phase. An output module provides a ground fault indication when all of the phases have a non-zero electrical energy sum for the selected interval.

Abstract: A multi-pole circuit breaker for a power distribution system having multiple line conductors carrying AC currents that are out of phase with each other, and a common neutral conductor, comprises first and second current sensors, a ground fault detection circuit, and an arcing fault detection circuit. The first current sensor is adapted to be coupled to both of the line conductors and to the neutral conductor and produces a first output signal indicative of the resultant of the electrical currents flowing in the line and neutral conductors. The ground fault detection circuit receives the first output signal and produces a trip signal in response to the detection of a ground fault.

Abstract: Methods, systems, and devices for controlling a serial arc fault in an electrical circuit are disclosed. In some embodiments, the methods include the following: a. measuring a current in the circuit; b. determining whether the current is below a predetermined value; c. if the current is below ten percent of the predetermined value, determining whether a countdown timer value indicated by a cell pointer value is equal to zero; d. if the countdown timer value is equal to zero, starting a countdown timer, advancing the cell pointer value by one, and restarting the method at step a.; e. if the countdown timer value is not equal to zero, determining whether the interruptions in the current are periodic; f. if the interruptions in the current are not periodic, checking whether an arc event countdown timer is running; and g. if the arc event countdown timer is running, tripping a circuit breaker.

Abstract: A bi-directional fault circuit interrupter comprising a first connection interface, a second connection interface, at least one fault circuit, and at least one switch which is movable from at least one first position to at least one second position to selectively electrically connect the fault circuit to either the first connection interface or the second connection interface. There are also a plurality of conductors configured to electrically connect the first connection interface to the switch and the second connection interface to the switch.

Abstract: A circuit breaker apparatus may be used to interrupt overcurrent and ground fault in a circuit. The circuit breaker apparatus may include an overcurrent coil for tripping the circuit breaker apparatus, a voltage coil also for tripping the circuit breaker apparatus located proximate to the overcurrent coil, and ground fault electronics connected to the voltage coil and structured to detect a ground fault in the circuit when the ground fault exceeds a threshold level. The ground fault electronics can be structured to send a trip signal to the voltage coil when a ground fault is detected, and the voltage coil can be structured to trip the circuit breaker apparatus when it receives the trip signal from the ground fault electronics.

Abstract: A circuit interrupter for interrupting current on a line conductor is provided. The circuit interrupter includes separable contacts, a trip mechanism, a bimetal, a microprocessor, a series arc detection sequence, a low-pass filter circuit, and a high-pass filter circuit. The trip mechanism selectively opens the separable contacts when activated. The series arc detection sequence is resident on the microprocessor and includes a plurality of series fault detection algorithms. The low-pass filter circuit provides a low-pass signal to the series arc detection sequence. The high-pass filter circuit provides a high-pass signal to the series arc detection sequence. The sequence selects a particular algorithm from the plurality of algorithms based on the low-pass signal. The sequence calculates a plurality of statistical features from the high-pass signal and sends an output signal to activate the trip mechanism based on a comparison of the plurality of statistical features to the particular algorithm.

Abstract: A ground fault detector and interrupter for a photovoltaic (PV) energy conversion system, method and apparatus are disclosed. In an exemplary embodiment, the system includes first and second inputs adapted to couple to a first and second rails of a PV array. An inverter is configured to convert DC power generated from the PV array to AC power. A ground fault detector and interrupter, which is coupled to the first and second rails and to the inverter, is configured to detect ground fault conditions in the PV array and to decouple the PV array from the remaining portion of the PV energy conversion system upon such detection. A known signal is coupled to the input of the ground fault detector and interrupter, and then sensed at the output of the ground fault detector and interrupter to determine whether components of the ground fault detector and interrupter are operating properly.

Abstract: A household appliance including at least one current sensor for measuring a fault current occurring in the appliance. A safety device which triggers a safety measure in the appliance in response to a predetermined detected fault current value.

Abstract: A circuit breaker includes for each neutral and phase power conductor, a current sensor sensing an alternating current flowing in a corresponding power conductor, a comparator determining whether the sensed alternating current is positive or negative, a rectifier rectifying the sensed alternating current to provide a rectified current value, and an analog-to-digital converter converting the rectified current value to a signed digital value having a positive sign. A processor cooperates with the comparators and the analog-to-digital converters and includes a routine that changes the positive sign of the signed digital value to a negative sign if the sensed alternating current is negative, adds the signed digital value for each power conductor to provide a sum, and employs the sum to determine whether to output a ground fault signal. The processor further cooperates with an operating mechanism to trip open separable contacts responsive to the ground fault signal.

Abstract: Systems and methods for detecting ground fault at the common DC bus in a high impedance ground system. A fault detection component can detect characteristics of an electrical signal including phase number (n) and fundamental frequency (H). A fast Fourier transform is performed at (n×H) and (2n×H), and the two values are compared. A healthy system (no ground fault) can display a large difference between (n×H) and (2n×H), while in an unhealthy system the difference can be minimal. A system and method of detecting variable phase number and fundamental frequency can be used in the calculation to perform the ground fault detection when these characteristics are variable.

Abstract: A circuit is disclosed for disconnecting a power source upon the detection of a leakage. The circuit comprises a disconnect switch for disconnecting the power source. A primary circuit controls the disconnect switch. A secondary circuit senses a leakage current. An optical switch interconnects the primary circuit and the secondary circuit for opening the disconnect switch upon the secondary circuit sensing a leakage current. The circuit is suitable for use as a leakage current detection and interruption circuit for completely electrically disconnecting and isolating the power source and the primary circuit from the secondary circuit.

Abstract: Solid state power controllers are described that include a switch controlled by a microcontroller and communication contacts. In one aspect of the invention, the microcontroller is galvanically isolated from the communication contacts using magnetoresistive isolation. In another aspect of the invention a number of solid state power controllers are connected to an external microcontroller to form a power distribution array. In addition, messages exchanged between the external microcontroller and the solid state power controllers can be used to configure the solid state power controllers and provide a user interface.

Abstract: A leakage current protection device with a single laminated magnetic core transformer that is formed by punch pressing an amorphous metal material, or a nanocrystalline soft metal material, in a high punch velocity press to form the ring laminations for the magnetic core. In a ground fault circuit interrupter, the single laminated magnetic core transformer serves as the input sensor for both the current imbalance detection circuitry and the low impedance ground fault protection circuitry.

Abstract: Disclosed herein is a ground fault protection circuit for an electrical distribution system, the electrical distribution system having a plurality of power sources each having an associated main circuit breaker and being electrically coupled to an associated load with a tie circuit breaker electrically coupled therebetween, the main and tie circuit breakers having associated therewith phase and neutral current transformers (CTs) for sensing an associated current. The ground fault protection circuit includes first, second and third auxiliary differential current transformers, each in signal communication with outputs of respective phase and neutral current transformers associated with respective first and second main circuit breakers and a tie circuit breaker. A control circuit has a defined topology that provides signal communication between each of the auxiliary differential current transformers.

Abstract: A solid state power control scheme is provided with a ground fault interrupt function. Essentially, if a neutral wire is associated with the power supply, the current is sensed in that neutral wire. The sensed neutral wire current is subtracted from a summed current on the power supply lines. If that result is greater than a predetermined limit, then the ground fault function is actuated and the circuit is opened. For power supplies, both those with and without neutral wires, the current is sensed by a shunt resistor on the power supply line.

Abstract: The present invention is directed to current interrupting devices with overcurrent protection. In one embodiment, a ground fault circuit interrupter (GFCI) is disclosed having both ground fault and overcurrent protection. The GFCI has a current detection circuit that includes a switch connected across the load phase terminal and the line neutral terminal of the device. A comparator compares a predefined threshold voltage to a sensed voltage based on a current through the line and load neutral terminals of the device. If the sensed voltage exceeds the predefined threshold, the comparator causes the switch to conduct thereby tripping the device, disconnecting the load from the line terminals and preventing the overcurrent condition from causing damage to the device and/or load.

Abstract: The invention refers to a method and an apparatus (1) for protecting people against leakage currents while using appliances such as home appliances or the like. The apparatus (1) is provided with a differential switch (20) normally open and a differential current transformer (39) which generates a signal proportional to the leakage current, an elaboration unit (50) interfaced with the latter acquires said signal and keeps the switch (20) closed until a dangerous condition is met, corresponding to an acquired signal having a magnitude greater than a limit value.