CN111200273B - Protective switchgear for low-voltage circuits for detection of series arc faults - Google Patents

Abstract

The invention relates to a protection switching device for low-voltage circuits, in particular for detecting series fault arcs, wherein a current measurement is carried out by means of a measuring resistor, via which the current of a conductor of the low-voltage circuit is conducted in order to determine the magnitude of the current of the low-voltage circuit. The measuring resistor is connected with the measuring circuit through at least one wire-shaped connecting line. The measurement circuit is powered by a power supply. The connection of the measuring circuit connected to the wire-like connection line is connected to the output of the power supply via a pull-up resistor, so that a break in the wire-like connection line can be determined and signaled by the voltage at the input of the measuring circuit exceeding a first threshold value.

Description

Protective switchgear for low-voltage circuits for detection of series arc faults

technical field

The invention relates to an inventive switching device for a low-voltage circuit, such as a fire switch or a circuit breaker, and a method according to the invention for protecting a switching device for a low-voltage circuit.

Background technique

Low voltage refers to voltages up to 1000 volts AC or up to 1500 volts DC. Low voltage means in particular a voltage greater than a low voltage having a value of 10 volts alternating current or 120 volts direct current.

A low-voltage circuit or a low-voltage network or a low-voltage system is a circuit whose measured current is up to 125 amperes, in particular up to 63 amperes.

An arc fault is an arc that occurs in a fault situation, i.e. an arc is formed due to a fault in an electrical circuit. For example due to faulty clamping, faults or faulty conductive connections in electrical circuits, eg junction boxes, switches or sockets of low-voltage circuits.

Instead of (disturbing) arcs, such as arcs that occur during normal operation of the network, for example during switching or at the brushes of electric motors.

A series arc fault is an arc that occurs in the current path of an electrical circuit, ie the current flowing through the arc also flows, for example, through a consumer. That is, if current flows in a "nearly interrupted" conductor, a so-called series fault arc forms at the point of interruption.

A fire switch is a relatively new type of protection device for electrical circuits or voltage networks which is used to identify such arc faults. The fire switch can be used in particular in domestic installations, for example in fuse boxes, in order to detect such faults and, if a fault exists or if a fault arc limit value is exceeded, to initiate the interruption of the circuit, to perform the interruption itself or to output Arc fault identification signal.

Line protective switches are well-known overcurrent protection devices which are used in electrical installation technology for low-voltage circuits. Line protection switches protect lines from damage due to excessive current and/or heating caused by short circuits. A line protection switch automatically disconnects a circuit in the event of an overload and/or short circuit. The line protection switch is a safety element that does not automatically reset.

In contrast to line protection switches, power switches are set for currents greater than 125A, and sometimes even from 63 Amps onwards. Therefore, the design of the line protection switch is simpler and utilizes fine wire technology.

用于针对长时间持续的过电流或热过载触发的双金属保护元件或双金属元件；用于在超过过电流界限值时或者在短路情况下短时触发的、具有线圈的电磁触发器；以及一个或多个灭弧室或用于灭弧的设备。此外，线路保护开关还具有用于要保护的电路的导体的连接元件等。Line protection switches are usually designed electromechanically with switching contacts or operating current triggers for interrupting the current

Bimetal protective elements or bimetallic elements for triggering against long-lasting overcurrents or thermal overloads; electromagnetic triggers with coils for brief triggering when an overcurrent limit value is exceeded or in the event of a short circuit; and One or more interrupters or devices for extinguishing arcs. Furthermore, the circuit breaker also has connection elements etc. for the conductors of the circuit to be protected.

In principle, circuit breakers monitor the magnitude of the current in a circuit and interrupt the circuit when a current limit value or a current-time interval limit value is exceeded.

Furthermore, fault current protective switches are known. Fault current protective switches monitor the sum of the currents in the circuit to be protected, which is usually zero, and interrupt the circuit when the fault current limit or differential current limit is exceeded, because there is usually a faulty and potentially life-threatening current flow .

It is known to combine a line protective switch with a fault current protective switch by inserting a fault current module into the line protective switch. Furthermore, a combined line protection switch and fault current switch is given, which is also called a residual current operated circuit breaker with overcurrent protection (RCBO for short).

In particular, fire switches and more and more new types of electronic circuit protection switches use measuring resistance to determine the magnitude of the current in the low-voltage circuit, in the case of a single-phase low-voltage circuit with a phase line and a neutral line, the low-voltage circuit is conducted via the measuring resistance current. Determines the magnitude of the current flow in a low voltage circuit from the voltage drop across a measured resistor of known resistance value. To this end, at least one or two connecting lines are connected to the measuring resistor, said connecting lines leading to the measuring circuit, which can be part of the control unit, for example. The control unit analyzes the voltage drop, determines the magnitude of the current or its equivalent, compares it with a current limit value, and initiates interruption of the circuit when the current limit value is exceeded. This can be done, for example, by a control unit. In a similar manner, the evaluation of the current (possibly together with other monitored variables) can be used to detect (series) fault arcs, as for example in a fire switch.

If the connecting line between the measuring resistor and the measuring circuit/control unit is damaged, the magnitude of the current flow cannot be determined and thus faults in the low-voltage circuit cannot be detected.

Contents of the invention

Therefore, the technical problem to be solved by the present invention is to improve protective switching devices, such as fire switches or line protective switches, in particular for detecting series fault arcs or overcurrents, which carry out the determination of the current magnitude by measuring the resistance , in particular the wire break detection of the connecting wire between the measuring resistor and the measuring circuit/control unit can be realized.

This technical problem is solved by a circuit breaker arrangement having the features according to the invention or by a method according to the invention.

According to the present invention, a protective switch device for low-voltage circuits, such as single-phase circuits, such as a fire switch or/and line protection switch is provided, which has:

- a first input connection for a first conductor (eg a phase conductor) of the low-voltage circuit, which is connected by a first line to a first output connection,

- a second input connection for a second conductor of the low-voltage circuit, such as a neutral conductor or a neutral conductor, which is connected by a second line to a second output connection,

- measuring resistance, which is inserted into the first or second line, in particular into the phase line, to determine the magnitude of the current (I) of the low-voltage circuit,

- a power supply connected on the input side to the first and second lines to supply energy to a control unit, in particular for recognizing series fault arcs or/and for recognizing overcurrent conditions,

- wherein the control unit has a first and a second measuring connection, which are connected to the measuring resistor.

According to the invention, the first or the second measuring connection is connected to the output of the power supply via a pull-up resistor.

In particular, the measuring connection connected to the connection on the output connection side of the measuring resistor is connected to the output of the power supply via a pull-up resistor.

A pull-up resistor is a resistor used to specify and pull up a potential. The potential can thus be set or pulled to a specific value. Pull-up resistors are also logically referred to as pull-down resistors, which pull the potential down, ie set it to a "lower" level. A defined potential should be applied in the event of a fault. The pull-up resistor is a "potential regulation resistor".

This has the advantage that in the event of a wire break of the connecting line between the measuring resistor and the measuring connector (fault situation), the measuring connector is pulled to a potential above (or below) the normal potential of the measuring resistor. A wire break is thus determined by a threshold comparison with a first threshold and, if necessary, signaled.

The present invention also provides an advantageous design solution.

In an advantageous refinement of the invention, the measuring resistor is connected via a wire-like connecting line to a measuring connection, which is connected via a pull-up resistor to an output of the power supply.

Wire-like connecting wires are electrical circuits in the form of rigid wires or flexible stranded wires, respectively with insulation or without insulation (lack of insulation).

Advantageously, the components can be arranged on a printed circuit board and the remaining components can advantageously be connected to the printed circuit board by means of connecting wires. The connection line can thus advantageously be monitored.

In an advantageous refinement of the invention, the power supply and control unit are arranged on a printed circuit board, which has at least part of the first and second lines.

This has the particular advantage that a particularly good integration of the components comprising the line can be achieved.

In an advantageous refinement of the invention, the measuring connections which are not connected via the pull-up resistor to the output of the power supply are at least partially connected via conductor tracks of the printed circuit board to the measuring resistor.

This has the particular advantage that a further advantageous integration can be achieved, so that only wire-shaped connecting lines, which can advantageously be monitored according to the invention, are required to measure the resistance.

In an advantageous refinement of the invention, the control unit has a measuring circuit, in particular using an ASIC or an amplifier, to determine the magnitude of the current or its equivalent value from the voltage drop across the measuring resistor.

This has the particular advantage of providing a compact and precise implementation for determining the magnitude of the current and for monitoring the voltage.

In an advantageous refinement of the invention, the control unit has a microprocessor. In particular, the processor can be connected to the measuring circuit.

This has the particular advantage that numerical analysis and programming are possible, whereby numerous functions can be implemented and limit values can be easily adjusted.

In an advantageous refinement of the invention, a pressure-limiting element is connected between the first and the second measuring connection. In particular, this can be realized in the form of one or two diodes. In particular in the case of two diodes, the two diodes can be connected in antiparallel. As the diode, a silicon diode, a Z diode, or the like can be used.

This has the particular advantage that a voltage limitation of the measuring circuit/control unit is achieved, whereby damage due to excessively high voltages is avoided.

In an advantageous refinement of the invention, the control unit is designed such that a series arc fault in the low-voltage circuit is detected and, when an arc fault limit value is exceeded, an arc fault detection signal is output, in particular the low-voltage circuit is interrupted.

This has the particular advantage that an arc fault protection function including monitoring is implemented.

In an advantageous configuration of the invention, the pull-up resistor has a resistance value between 100 ohms and 10 megaohms, in particular a resistance value between 1 kohms and 1 megaohms, more particularly 10 kohms to 100 kohms ohms between and including values of 10 kohms and 100 kohms.

This has the particular advantage that there are resistor values which cause a small influence on the measurement result but which nevertheless enable the pull-up function.

In an advantageous refinement of the invention, the pull-up resistor has a resistance value at least 1000 times, in particular 10000 times, 100000 times, 1000000 times, 10000000 times or 100000000 times the resistance value of the measuring resistor.

This has the particular advantage that there are also resistor values which have a lesser influence on the measurement result but which nevertheless enable the pull-up function.

In an advantageous refinement of the invention, the measuring resistor has a constant resistance value at least in the temperature range.

The temperature range refers to the application temperature range of the protective switching device. In particular, a temperature range of -25°C to 70°C, 105°C or 150°C is meant.

A constant resistance value refers to a resistance value that changes only slightly. In particular, this is common in measuring resistances. In particular, constant resistance refers to a resistance having a temperature coefficient of up to 200 ppm per Kelvin, 150 ppm per Kelvin, 100 ppm per Kelvin, 75 ppm per Kelvin, or even better 50 ppm per Kelvin.

Alternatively or in particular a temperature coefficient of α=(-80...+40)·10 ⁻⁶ K ⁻¹ or α=±50·10 ⁻⁶ K ⁻¹ is meant.

This has the particular advantage that precise and reproducible current measurements can be achieved at many locations of use and under varying ambient conditions.

In an advantageous refinement of the invention, the voltage drop across the measuring resistor is a voltage proportional to the current.

This has the particular advantage that precise measurements can be achieved, especially by means of linear components.

In an advantageous refinement of the invention, the measuring resistor has a bimetal or a bimetal protection element.

This has the particular advantage that a particularly simple current measurement can be realized, wherein in addition a thermoelectric overcurrent protection function can also be realized.

In an advantageous refinement of the invention, the bimetal protective element is connected in series with the measuring resistor.

This has the particular advantage that a particularly precise current measurement and a thermoelectric overcurrent protection function can be achieved.

In an advantageous refinement of the invention, a wire break detection signal is output when it is detected that the input voltage at the measuring connection exceeds a first threshold value. In particular, an optical, electrical (switching contact) or acoustic signal is emitted in the event of a wire break detection signal.

This has the particular advantage that an alarm can be output in the event of a wire break.

In an advantageous refinement of the invention, an interrupting unit is provided for interrupting the low-voltage circuit, which interrupts the low-voltage circuit, in particular when a wire break detection signal is present.

This has the particular advantage that the circuit is interrupted, ie protected, in the event of a wire break and subsequent lack of monitoring.

In an advantageous refinement of the invention, the interrupting unit is connected upstream of the input side of the power supply or/and has contacts for interrupting the first and/or second line.

This has the particular advantage that the protective switching device is not energized in the event of a fault.

In an advantageous refinement of the invention, the low-voltage circuit is a low-voltage AC circuit.

This has the particular advantage that the invention is particularly well suited for AC circuits.

In an advantageous refinement of the invention, the protective switch device is a fire switch, a circuit breaker, a power switch or a fault current breaker. Alternatively, the protective switching device has a fire protection function, a line protection function or a fault current protection function.

This has the particular advantage that the invention can be used especially in the mentioned arrangement for protecting electrical circuits.

Furthermore, according to the invention, a parallel method for protecting switching devices for low-voltage circuits is claimed,

- wherein the current measurement is performed by means of a measuring resistor via which a current of a conductor of the low-voltage circuit is conducted to determine the magnitude of the current of the low-voltage circuit,

- the measuring resistance is connected to the measuring circuit via at least one wire-like connecting line,

- The measurement circuit is powered by the power supply.

According to the invention, the connection of the measurement circuit connected to the wire-like connection is connected via a pull-up resistor to the output of the power supply, so that a break in the wire-like connection can be determined by the voltage at the input of the measurement circuit exceeding a first threshold value and transmit signal.

In an advantageous refinement of the invention, the signal is output via an optical display, activation of a switching contact or/and interruption of an electrical circuit.

All configurations of the invention lead to an improvement of the protective switching device.

Description of drawings

The described characteristics, features and advantages of the present invention as well as their implementations will be more clearly and distinctly understood in conjunction with the following description of the embodiments explained in detail with reference to the accompanying drawings.

Here, in the attached picture:

Figure 1 shows a first diagram for explaining the protective switching device of the present invention,

Figure 2 shows a second diagram for explaining the protective switching device of the present invention,

FIG. 3 shows a third diagram for explaining the protective switching device of the invention.

Detailed ways

Figure 1 shows a diagram of a protective switching device SG for a low-voltage circuit, such as a fire switch, a line protection switch or a combined fire switch/line protection switch, in particular for the detection of series faults Arc, which has:

- a first input connection E1 for the first conductor L1 of the low-voltage circuit, which is connected to the first output connection A1 by a first line LT1,

- a second input connection E2 for the second conductor N of the low-voltage circuit, which is connected to the second output connection A2 via a second line LT2,

- a measuring resistor MR that can be inserted into the first or second line LT1, LT2, in the example according to FIG. 1 a measuring resistor is inserted into the first line LT1 in order to determine the magnitude of the current of the low-voltage circuit,

- a power supply NT connected on the input side to the first and second lines LT1, LT2 for supplying energy to a control unit SE designed especially for detecting series fault arcs or/and overcurrents,

In this case, the control unit SE has a first and a second measuring connection ME, MA, which are connected to the respective input-connection-side or output-connection-side connection of the measuring resistor MR.

In this example, the first measuring connection ME is connected to the input-connection-side end of the first line LT1 ; the second measuring connection MA is connected to the output-connection-side end of the first line LT1 .

According to the invention, the first or the second measuring connection is connected to the output of the power supply NT via a pull-up resistor PR. In the example according to FIG. 1 , the second measuring connection MA is connected to the output of the power supply NT via a pull-up resistor PR.

The control unit SE can have a measuring circuit MS and a microprocessor MCU, which are each supplied with energy, for example, by a power supply NT.

FIG. 2 shows the arrangement according to FIG. 1 , with the difference that the measuring resistor MR is connected via a wire-like connecting line DVL to a measuring connection, which is connected via a pull-up resistor PR to the output of the power supply NT.

In this example, the second measuring connection MA is connected to the output-connection-side connection of the measuring resistor MR via a wire-like connecting line DVL.

It is also possible to connect a series resistance VR upstream of one or both measuring connections; in this example, the second measuring connection MA has a series resistance VR, so that the wire-like connecting line DVL is connected to the second measuring connection MA via the series resistance VR.

Furthermore, the power supply NT and the control unit SE are arranged on a printed circuit board LP having at least a part of the first and second lines LT1, LT2. Furthermore, the measuring connections which are not connected via the pull-up resistor PR to the output of the power supply NT are at least partially connected via the conductor tracks LB of the printed circuit board LP to the measuring resistor MR. In this example, the first measuring connection ME is connected to the connection on the input connection side of the measuring resistor MR via a conductor track LB and a first line LT1 , which can also be embodied as a conductor track of a printed circuit board.

Furthermore, the control unit SE has a measurement circuit using an ASIC (ASICA) to determine the magnitude of the current or its equivalent value from the voltage drop across the measurement resistor MR. The ASIC interfaces with the microprocessor MCU.

Furthermore, a pressure-limiting element D1 , D2 is connected between the first and the second measuring connection. In the example according to FIG. 2 there are voltage limiting elements in the form of (one or) two diodes D1 , D2 . In an example, the two diodes D1 , D2 are connected in anti-parallel for voltage limiting.

In the example according to FIG. 2 , the measuring resistor is implemented in the form of a bimetal or bimetal protective element BM, wherein, as shown in the example, the bimetal or bimetal protective element does not have to be located on the printed circuit board LP. The bimetallic or bimetallic protective element is arranged on the outside of the printed circuit board LP and is connected on the output terminal side (A1) via a wire-like connecting line (DVL) to the measuring terminal, in particular to the power supply NT via a pull-up resistor PR. The measuring connection is connected; in this example the second measuring connection MA.

Furthermore, an interruption unit UE is provided for interrupting the low-voltage circuit. In particular, the interrupting unit can interrupt the low-voltage circuit in the event of a wire break detection signal. In the example according to FIG. 2 the interruption unit UE is connected before the input side of the power supply NT. As shown in FIG. 2 , the interrupting unit can have contacts for interrupting the first and/or second line LT1 , LT2 .

FIG. 3 shows the arrangement according to FIG. 2 , with the difference that the bimetal protective element BM is connected in series with the measuring resistor MR. In this case, a wire-shaped connecting line DVL is installed at the connection point between the measuring resistor MR and the bimetallic protective element BM.

In the example of FIG. 3 , the measuring circuit MS of the control unit SE is realized by using an amplifier AMP for determining the magnitude of the current or its equivalent value from the voltage drop across the measuring resistor MR.

In this case, the measuring resistor MR is connected on the other side via a line LT1 and a conductor track LB to the first measuring input ME of the control unit SE or of the measuring circuit MS, for example the amplifier AMP.

In this case, the measuring resistor MR and/or the bimetal protection element BM can be arranged wholly or partially on the printed circuit board LP.

In one refinement, the control unit SE is designed to detect a series arc fault in the low-voltage circuit and to output an arc fault detection signal when an arc fault limit value is exceeded, in particular by means that can also be arranged in the protective switchgear The interruption unit UE outside the casing of the SG interrupts the low-voltage circuit.

The measuring resistor MR advantageously has a resistance value in the milliohm range. For example in the range of 1 to 10 or 100 milliohms. The higher the measuring current of the protective switching device, the lower the resistance value of the measuring resistor should be.

The pull-up resistor PR advantageously has a resistance value between 100 ohm and 10 megohm, in particular between 1 kohm and 1 megohm, more particularly between 10 kohm and 100 kohm or 1 megohm Values (including 10 kΩ and 100 kΩ or 1 MΩ).

The pull-up resistor PR advantageously has a resistance value at least 1000 times, in particular 10000 times, 100000 times, 1000,000 times, 10000000 times or 100000000 times the resistance value of the measuring resistor MR. The higher the value, the smaller the measurement error. On the other hand, a stable potential must be provided.

The voltage output by the power supply NT may be, for example, 3.3 volts. Silicon diodes, for example, can be used as voltage-limiting elements. Silicon diodes typically have a forward voltage of 0.7 volts. When it is detected that the input voltage at the measuring connection exceeds a first threshold value, a wire break detection signal is output. In this example, the first threshold may have a magnitude of 0.5 or 0.6 volts. The first threshold should be lower than the voltage limiting value of the voltage limiting element.

In the event of wire break detection, for example optical (eg LED), electrical (switching contacts on/off) or/and acoustic signals are emitted.

It can also interrupt low voltage circuits. Due to the absence of monitoring through a wire break, a safe state is created in the circuit.

Advantageously, the invention can be implemented as a method.

The present invention is explained again below in another way. Measuring resistors (shunts) are used to measure current (load current) in low-voltage circuits. In some cases, the connection to the measuring resistor may be damaged/damaged. For example, if the measurement resistor is connected to an electric wire (wire-shaped connecting wire), the electric wire may break. This type of fault cannot be recognized. In the event of such a failure, if there is no identifiable indication, the device cannot be put into service/damaged.

According to the invention, a so-called pull-up resistor with a much higher resistance than the measuring resistor is added at the input of the control unit/measuring circuit or the current conditioning circuit. When the measurement resistor is connected to the measurement circuit, the effect of the pull-up resistor can be ignored. When the connection to the measuring resistor is interrupted, the voltage on the measuring circuit will be very high, corresponding to or proportional to the output voltage of the power supply (possibly, proportional to a voltage divider with a pull-up resistor, that is to say the voltage decreases up). This high and constant voltage, in particular a direct voltage, can be detected by the measuring circuit or by a microprocessor MCU connected at the output of the measuring circuit.

A wire breakage recognition signal can be output.

The measuring resistor can be bimetallic. The measurement circuit can be an analog circuit with resistors, an operational amplifier circuit or a fully integrated finishing IC such as an ASIC.

A possible implementation of the invention consists in its use in a fire switch for detecting series arc faults. Furthermore, applications are made in circuit breakers or combined fire switch/circuit breakers, for example in housings with a width of 1 TE.

In the case of a pure circuit breaker, the measuring resistor can be implemented as a bimetal of the circuit breaker.

In the case of fire switching functions, the control unit or the measuring circuit can be designed as an ASIC for the arc fault detection function including amplification and possible offset addition.

The invention can also be used to measure energy. Here, the amplifier Amp is used. Here, the power supply can generate a precise reference voltage Vref and output it to the amplifier so that precise current measurement for energy determination can be achieved.

Especially in this case, in addition to the positive voltage V+, a negative voltage V- can also be supplied to the amplifier to accurately measure the negative component of the current/load current.

In the amplifier, a reference voltage Vref, eg half the supply voltage of the power supply, is added to the output signal so that the measurement can be achieved or improved by the microprocessor MCU.

The invention makes it possible to identify and signal a defective device. Otherwise, the equipment will be damaged without instructions. This increases the overall security level. The invention can be implemented simply by adding resistors.

Although the invention has been illustrated and described in detail by way of example, the invention is not limited to the disclosed examples and a person skilled in the art can derive other variants therefrom without departing from the scope of protection of the invention.

Claims (30)

1. A protective switch device for low-voltage circuits, the protective switch device has: - a first input connection (E1) for a first conductor (L1) of said low-voltage circuit, which is connected to a first output connection (A1) by a first line (LT1), - a second input connection (E2) for a second conductor (N) of said low-voltage circuit, which is connected to a second output connection (A2) by a second line (LT2), - a measuring resistor (MR) inserted into the first or second line (LT1, LT2) to determine the magnitude of the current of said low-voltage circuit, - a power supply (NT) connected on the input side to the first and second lines (LT1, LT2) to supply energy to the control unit (SE), - the control unit (SE) has a first and a second measuring connection connected to the measuring resistor (MR), It is characterized in that, The first or second measurement connector is connected to the output terminal of the power supply (NT) via a pull-up resistor (PR), When it is recognized that the input voltage at the measuring connector exceeds a first threshold value, a wire breakage recognition signal is output, In the event of a wire break detection signal, an optical, electrical or acoustic signal is emitted. 2. The protective switchgear according to claim 1, characterized in that the measuring resistor (MR) is connected to the measuring terminal via a wire-like connecting line (DVL) via the pull-up resistor ( PR) is connected to the output terminal of the power supply (NT). 3. Protective switching device according to claim 1, characterized in that the power supply (NT) and the control unit (SE) are arranged on a printed circuit board (LP) with a first and at least a part of the second line (LT1, LT2). 4. Protective switching device according to claim 3, characterized in that the measuring connection not connected via the pull-up resistor (PR) to the output of the power supply (NT) is at least partly via the printed circuit board The printed conductor (LB) of (LP) is connected to the measuring resistor (MR). 5. The protective switchgear according to any one of claims 1 to 4, characterized in that the control unit (SE) has a measuring circuit (MS) for measuring the voltage drop across the measuring resistor (MR) To determine the magnitude of the current or its equivalent. 6. Protective switching device according to claim 5, characterized in that the measuring circuit (MS) uses an ASIC (ASICA) or an amplifier (AMP). 7. The protective switchgear according to any one of claims 1 to 4, characterized in that the control unit (SE) has a microprocessor (MCU). 8. The protective switching device as claimed in claim 1, characterized in that a voltage-limiting element (D1, D2) is connected between the first and the second measuring connection. 9. The protective switching device according to claim 8, characterized in that the voltage limiting element (D1, D2) is a voltage limiting element in the form of one or two diodes, wherein in the case of two diodes, These two diodes are connected in antiparallel. 10. The protective switching device according to any one of claims 1 to 4, characterized in that the control unit (SE) is designed such that a series arc fault in the low-voltage circuit is determined and in excess of the fault When the arc limit value is reached, the fault arc identification signal is output. 11. The protective switching device according to any one of claims 1 to 4, characterized in that the control unit (SE) is designed such that a series fault arc in the low-voltage circuit is determined, and in excess of the fault The low voltage circuit is interrupted when the arc threshold is reached. 12. The protective switching device according to any one of claims 1 to 4, characterized in that the pull-up resistor (PR) has a resistance value between 100 ohms and 10 megohms. 13. The protective switching device according to any one of claims 1 to 4, characterized in that the pull-up resistor (PR) has a resistance value between 1 kohm and 1 megaohm. 14. The protective switching device according to any one of claims 1 to 4, characterized in that the pull-up resistor (PR) has a resistance between 10 kohms and 100 kohms inclusive. value. 15. The protective switching device according to any one of claims 1 to 4, characterized in that the pull-up resistor (PR) has a resistance value at least 1000 times the resistance value of the measuring resistor (MR) . 16. The protective switching device according to any one of claims 1 to 4, characterized in that the pull-up resistor (PR) has a resistance value at least 10000 times the resistance value of the measuring resistor (MR) . 17. The protective switching device according to any one of claims 1 to 4, characterized in that the pull-up resistor (PR) has a resistance value at least 100000 times the resistance value of the measuring resistor (MR) . 18. The protective switching device according to any one of claims 1 to 4, characterized in that the pull-up resistor (PR) has a resistance value at least 1000000 times the resistance value of the measuring resistor (MR) . 19. The protective switching device according to any one of claims 1 to 4, characterized in that the pull-up resistor (PR) has a resistance value at least 10000000 times the resistance value of the measuring resistor (MR) . 20. The protective switching device according to any one of claims 1 to 4, characterized in that the pull-up resistor (PR) has a resistance value at least 100000000 times the resistance value of the measuring resistor (MR) . 21. The protective switching device as claimed in claim 1, characterized in that the measuring resistor (MR) has a constant resistance value at least in the temperature range. 22. The protective switching device as claimed in any one of claims 1 to 4, characterized in that the voltage drop across the measuring resistor (MR) is a voltage proportional to the current. 23. The protective switching device as claimed in one of claims 1 to 4, characterized in that the measuring resistor (MR) has a bimetal or is a bimetal protective element (BM). 24. The protective switching device as claimed in any one of claims 1 to 4, characterized in that a bimetal protective element (BM) is connected in series with the measuring resistor (MR). 25. The protective switchgear according to claim 1, characterized in that an interruption unit (UE) is provided for interrupting the low-voltage circuit, which interrupts the low-voltage circuit when a wire break detection signal is present. 26. Protective switchgear according to claim 25, characterized in that the interruption unit (UE) is connected before the input side of the power supply (NT), or/and There are contacts for interrupting the first and/or second line. 27. The protective switchgear according to any one of claims 1 to 4, characterized in that the low voltage circuit is a low voltage AC circuit. 28. The protection switch device according to any one of claims 1 to 4, characterized in that, the protection switch device is a fire switch, a line protection switch, a power switch or a fault current protection switch, or the protection switch device It has fire protection function, line protection function or fault current protection function. 29. A method for protecting a switching device for a low voltage circuit, - wherein the current measurement is performed by means of a measuring resistor (MR) via which a current of a conductor of the low-voltage circuit is conducted to determine the magnitude of the current of the low-voltage circuit, - said measuring resistor (MR) is connected to the measuring circuit (MS) via at least one wire-like connecting line (DVL), - energizing said measurement circuit (MS) via a power supply, It is characterized in that, The connector of the measurement circuit (MS) connected to the wire-like connection line (DVL) is connected to the output terminal of the power supply (NT) via a pull-up resistor (PR), so that the input terminal of the measurement circuit (MS) can pass The voltage of the DVL exceeds a first threshold to determine and signal a break in the wire-like connection line (DVL). 30. The method as claimed in claim 29, characterized in that the signaling is performed by an optical display, by activating a switch contact or/and by interrupting the low-voltage circuit.

Images