GB2580206A

GB2580206A - Protective switching device for a low-voltage circuit for identifying series arcing faults

Info

Publication number: GB2580206A
Application number: GB1915728.8A
Authority: GB
Inventors: Festl Florian; Huber Markus
Original assignee: Siemens AG
Current assignee: Siemens AG
Priority date: 2018-11-16
Filing date: 2019-10-30
Publication date: 2020-07-15
Anticipated expiration: 2039-10-30
Also published as: DE102018219692A1; GB201915728D0; GB2580206B; CN111200273B; CN111200273A

Abstract

A protective switching device for a low voltage circuit, in particular for identifying series arcing faults, includes a measurement resistor BM for measuring current in a line L1 and a measurement circuit ASICA connected to the measurement resistor via two measurement connections MA, ME and a wire connecting line DVL. The measurement circuit is supplied by a power supply NT and the wire-like connecting line DVL is connected to an output of the power supply via a pull-up resistor PR, such that a fracture in the connecting line can be detected if the voltage at the input MA of the measurement circuit exceeds a threshold. A voltage limiter with a pair of opposed diodes D1, D2 may be included between terminals MA, ME. The pull-up resistor has much larger resistance, at least 1000 times, than the measurement resistor. A break in wire DVL may be indicated by optical, electrical or acoustic signalling or by activating the switch UE to interrupt the low voltage circuit.

Description

Protective switching device for a low-voltage circuit for identifying series arcing faults

Technical field

The invention relates to a protective switching device for a low-voltage circuit, such as an arc fault detection device or a line circuit breaker, and to a method for a protective switching device for a low-voltage circuit.

Background

Low voltage means voltages of up to 1000 volts AC or up to 1500 volts DC. Low voltage means, in particular, voltages greater than extra-low voltage, with values of 50 volts AC or 120 volts

DC

Low-voltage circuit or system or installation means circuits with measurement currents of up to 125 amperes, specifically up to 63 amperes.

Arcing faults means arcs that occur in the event of a fault, that is to say arise due to faults in the circuit. For example, due to poorly clamped, faulty or poorly conducting connections or contacts in the electric circuit, for example in junction boxes, switches or sockets of the low-voltage circuit. It does not mean (fault) arcs as occur, for example, during regular operation of a system, for example during switching or at the brushes of a motor.

Series arcing faults means arcs that occur in the current path of the circuit, that is to say the current that, for example, also flows via a consumer, flows via the arc. That is to say if a current flows in an "almost interrupted" conductor, what is known as a series arcing fault arises at the interruption point.

Arc fault detection devices are relatively novel protection devices for circuits or voltage systems and serve to identify such arcing faults. Arc fault detection devices can be used, in particular, in domestic installation devices, such as fuse boxes, in order to identify such faults and, in the presence of a fault or exceedance of an arcing fault limit value, to permit initiation to interrupt the electric circuit, to interrupt it itself or to output an arcing fault identification signal.

Line circuit breakers are well known overcurrent protection devices that are used in electrical installation technology in low-voltage circuits. They protect lines against damage caused by -2 -heating as a result of too high a current and/or short circuit. A line circuit breaker can automatically disconnect the circuit in the event of overloading and/or short circuit. A line circuit breaker is a non-automatically resetting fuse element.

In contrast to line circuit breakers, circuit breakers are provided for currents greater than 125 A, sometimes even from as little as 63 amperes. Line circuit breakers are therefore of a more simple and delicate design.

Line circuit breakers are generally of electromechanical design and have a switching contact or open-circuit shunt release for interrupting the electric current, a bimetal protection element or bimetal element for tripping in the case of an overcurrent remaining for a long time or respectively in the event of thermal overloading, an electromagnetic trip with a coil for temporarily tripping when an overcurrent limit value is exceeded or in the event of a short circuit, and one or more arc quenching chambers or devices for quenching arcs. Also connection elements for conductors of the electric circuit to be protected etc. In principle, line circuit breakers monitor the magnitude of the electric current in the circuit and interrupt the circuit when current limit values or current-time limit values are exceeded.

Residual current devices are also known. These monitor the total current in the circuit that is to be protected, the total current generally being zero, and interrupt the electric circuit when a residual current limit value or differential current limit value is exceeded since there is then generally a faulty and possibly dangerous outward flow of current.

It is known to combine line circuit breakers with residual current devices by virtue of plugging residual current modules to the line circuit breaker. There are also combined line circuit breakers and residual current devices, which are also referred to as residual current operated circuit breakers with overcurrent protection, RCBO for short.

In particular, arc fault detection devices and increasingly also novel electronic line circuit breakers use measurement resistors to ascertain the magnitude of the current in the low-voltage circuit, the current of the low-voltage circuit being conducted via said measurement resistors in the case of single-phase low-voltage circuits with a phase conductor and the neutral conductor. The magnitude of the electric current in the low-voltage circuit is ascertained from the voltage drop across the known resistance value of the measurement resistor. To this end, -3 -at least one, or two, connecting line(s) are connected to the measurement resistor, said connecting line or lines being conducted to a measurement circuit, which may be, for example, part of a control unit. Said measurement circuit evaluates the voltage drop, ascertains the magnitude of the electric current or an equivalent thereto that is compared with current limit values and an interruption of the electric circuit is initiated when said current limit values are exceeded. For example, this can be effected by way of a control unit. In an analogous manner, the evaluation of the current, possibly with other monitored values, can be used to identify (series) arcing faults, such as in an arc fault detection device, for example.

If a connecting line between the measurement resistor and the measurement circuit/control unit is faulty, the magnitude of the current cannot be ascertained, as a result of which faults in the electric low-voltage circuit cannot be detected.

Summary

It would be desirable to improve a protective switching device, in particular for identifying series arcing faults or overcurrents, such as an arc fault detection device or line circuit breaker, which ascertains the magnitude of the current by way of a measurement resistor, in particular to make it possible to identify a wire fracture of connecting lines between the measurement resistor and the measurement circuit/control unit.

According to the invention, a protective switching device for a low-voltage circuit, such as a single-phase circuit, is provided, such as an arc fault detection device or/and line circuit breaker, having: -a first input connection, which is connected to a first output connection by way of a first line, for a first conductor, such as a phase conductor, of the low-voltage circuit, -a second input connection, which is connected to a second output connection by way of a second line, for a second conductor, such as a neutral conductor, of the low-voltage circuit, -a measurement resistor, which is inserted in the first or second line, in particular into the phase line, for ascertaining the magnitude of the current (I) of the low-voltage circuit, -a power supply unit, the input side of which is connected to the first and second line, for supplying energy to a control unit, in particular for identifying series arcing faults or/and for identifying overcurrent conditions, -wherein the control unit has a first and a second measurement connection, which are connected to the measurement resistor. -4 -

According to the invention, the first or second measurement connection is connected to an output of the power supply unit via a pull-up resistor. In particular, the measurement connection that is connected to the output-connection-side connection of the measurement resistor is connected to the output of the power supply unit via the pull-up resistor.

A pull-up resistor means a resistor for setting and raising a potential. A potential can be set or pulled to a specific value thereby. A pull-up resistor would also logically mean a pull-down resistor, which pulls down a potential, that is to say sets it to a "lower' level. In the event of a fault, a defined potential should be applied. The pull-up resistor is a "potential setting resistor".

This has the advantage that, in the case of a wire fracture (fault event) in the connecting line between the measurement resistor and the measurement connection, the measurement connection is drawn to a potential above (or below) the usual potential of the measurement resistor. A wire fracture can thus be ascertained and, where necessary, signaled by way of threshold value comparison with a first threshold value.

In one advantageous configuration of the invention, the measurement resistor is connected by way of a wire-like connecting line to the measurement connection that is connected to the output of the power supply unit via the pull-up resistor.

A wire-like connecting line means an electrical line in the form of a rigid wire or a flexible Litz-wire, respectively with or without insulation (lack of insulation).

Components can advantageously be arranged on a printed circuit board; remaining components can advantageously be connected to the printed circuit board by way of connecting lines. The connecting line can thus advantageously be monitored.

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

This has the particular advantage that a particularly good integration of the components including the line is made possible. -5 -

In one advantageous configuration of the invention, the measurement connection that is not connected to the output of the power supply unit via the pull-up resistor is at least partly connected to the measurement resistor via a conductor track of the printed circuit board.

This has the particular advantage that further advantageous integration is made possible, with the result that only a wire-like connecting line, which can advantageously be monitored by way of the invention, to the measurement resistor is necessary.

In one advantageous configuration of the invention, the control unit has a measurement circuit, in particular using an ASIC or an amplifier, to ascertain the magnitude of the current or an equivalent from the voltage drop across the measurement resistor.

This has the particular advantage that a compact and precise implementation for ascertaining the magnitude of the current and for the voltage monitoring is provided.

In one advantageous configuration of the invention, the control unit has a microprocessor. Said processor can be connected, in particular, to the measurement circuit.

This has the particular advantage that digital evaluation and programming is made possible, as a result of which many features can be implemented and limit values can be adjusted simply.

In one advantageous configuration of the invention, a voltage limiting element is connected between the first and second measurement connection. In particular, this can be effected in the form of one or two diodes. Particularly in the case of two diodes, these can be connected in antiparallel. Diodes used can be silicon diodes, Z diodes etc. This has the particular advantage that voltage limitation of the measurement circuit/control unit is effected, as a result of which instances of destruction due to excessively high voltages are prevented.

In one advantageous configuration of the invention, the control unit is configured in such a way that series arcing faults in the low-voltage circuit are identified and, when an arcing fault limit -6 -value is exceeded, an arcing fault identification signal is output, in particular the low-voltage circuit is interrupted.

This has the particular advantage that an arcing fault protection function including monitoring is carried out.

In one advantageous configuration of the invention, the pull-up resistor has a resistance value between 100 ohm and 10 megaohm, in particular between 1 kiloohm and 1 megaohm, more specifically values between 10 kiloohm and 100 kiloohm inclusive.

This has the particular advantage that resistance values that cause low interference in the measurement results and still make the pull-up function possible are present.

In one advantageous configuration of the invention, the pull-up resistor has a resistance value at least 1000 times, in particular 10,000 times, 100,000 times, 1,000,000 times, 10,000,000 times, or 100,000,000 times the resistance value of the measurement resistor.

This has the particular advantage that likewise resistance values that cause low interference of the measurement results and still make the pull-up function possible are present.

In one advantageous configuration of the invention, the measurement resistor has a resistance value that is constant at least in a temperature range.

Temperature range means the temperature range of use of the protective switching device. In particular, temperature ranges of -25°C to 70°C, 105°C or 150°C are meant.

Constant resistance value means a resistance value that changes only slightly. In particular, as is usual in the case of measurement resistors. In particular, resistors with temperature coefficients 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 are meant. Alternatively or more specifically, temperature coefficients of a = (-80.. +40) .10-6 K-1 or a = ± 50.10-6K-1 are meant.

This has the particular advantage that a precise and reproducible current measurement is made possible in many locations of use and in the case of changing environmental conditions.

In one advantageous configuration of the invention, a voltage that is proportional to the current is dropped across the measurement resistor.

This has the particular advantage that a precise measurement, in particular by way of linear components, is made possible.

In one advantageous configuration of the invention, the measurement resistor has a bimetal or is a bimetal protection element.

This has the particular advantage that a particularly simple current measurement is made possible, wherein a thermoelectric overcurrent protection function is also made possible.

In one advantageous configuration of the invention, a bimetal protection element is connected in series with the measurement resistor.

This has the particular advantage that a particularly precise current measurement and thermoelectric overcurrent protection function is made possible.

In one advantageous configuration of the invention, when an input voltage at the measurement connections that exceeds a first threshold value is identified, a wire fracture identification signal is output. In particular, optical, electrical (switching contact) or acoustic signaling is effected in the presence of the wire fracture identification signal.

This has the particular advantage that a warning can be output in the case of a wire fracture.

In one advantageous configuration of the invention, an interruption unit for interrupting the low-voltage circuit is provided, which interrupts the low-voltage circuit in particular in the presence of a wire fracture identification signal.

This has the particular advantage that the circuit is interrupted, that is to say protected, in the case of a wire fracture and subsequent lack of monitoring. -8 -

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

This has the particular advantage that the protective switching device has no current in the event of a fault.

In one advantageous configuration 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 one advantageous configuration of the invention, the protective switching device is an arc fault detection device, a line circuit breaker, a circuit breaker or a residual current device.

Alternatively, said protective switching device has an arc fault detection, line protection or residual current protection functionality.

This has the particular advantage that the invention can be used to protect circuits in particular in the mentioned devices.

According to the invention, a parallel method for a protective switching device for a low-voltage circuit is also claimed, - in which a current measurement is carried out by means of a measurement resistor, via which the current of a conductor of the low-voltage circuit is conducted, to ascertain the magnitude of the current of the low-voltage circuit, - the measurement resistor is connected to a measurement circuit by way of at least one wirelike connecting line, -the measurement circuit is supplied with energy by way of a power supply unit.

According to the invention, the connection of the measurement circuit to which the wire-like connecting line is connected is connected to an output of the power supply unit via a pull-up resistor such that a fracture in the wire-like connecting line can be ascertained by way of a voltage at the input of the measurement circuit that exceeds a first threshold value and signaled. -9 -

In one advantageous configuration of the invention, the signaling is effected by way of an optical display, activation of a switching contact or/and interruption of the electrical circuit.

All of the configurations, both in dependent form with reference back to the independent patent claims and with reference back to just single features or combinations of features of patent claims, bring about an improvement in a protective switching device.

Brief description of the drawincis

The described properties, features and advantages of this invention and the manner in which they are achieved become more clearly and distinctly comprehensible in conjunction with the following description of the exemplary embodiments, which are explained in more detail in connection with the drawing.

Here, in the drawing: figure 1 shows a first illustration of a protective switching device for explanation of the invention, figure 2 shows a second illustration of a protective switching device for explanation of the invention, figure 3 shows a third illustration of a protective switching device for explanation of the invention.

Detailed description

Figure 1 shows an illustration of a protective switching device SG for a low-voltage circuit, such as, for example, an arc fault detection device, a line circuit breaker or combined arc fault detection device/line circuit breaker, in particular for identifying series arcing faults, having: -a first input connection El, which is connected to a first output connection Al by way of a first line LT1, for a first conductor Ll of the low-voltage circuit, -a second input connection E2, which is connected to a second output connection A2 by way of a second line LT2, for a second conductor N of the low-voltage circuit, -10 - -a measurement resistor MR, which can be inserted in the first or second line LT1, LT2, in the example in accordance with figure 1 it is inserted in the first line LT1, for ascertaining the magnitude of the current of the low-voltage circuit, -a power supply unit NT, the input side of which is connected to the first and second line LT1, LT2, for supplying energy to a control unit SE, which is configured in particular for identifying series arcing faults or/and overcurrents, -wherein the control unit SE has a first and a second measurement connection ME, MA, which are connected to the respective input-connection-side or output-connection-side connections of the measurement resistor MR.

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

According to the invention, the first or second measurement connection is connected to an output of the power supply unit NT via a pull-up resistor PR. In the example in accordance with figure 1, the second measurement connection MA is connected to an output of the power supply unit NT via the pull-up resistor PR.

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

Figure 2 shows an arrangement in accordance with figure 1 with the difference that the measurement resistor MR is connected by way of a wire-like connecting line DVL to the measurement connection that is connected to the output of the power supply unit Ni via the pull-up resistor PR.

In the example, the second measurement connection MA is connected to the outputconnection-side connection of the measurement resistor MR via the wire-like connecting line DVL.

A series resistor VR can also be connected upstream of one or both measurement connections; in the example, the second measurement connection MA has a series resistor VR such that the wire-like connecting line DVL is connected to the second measurement connection MA via the series resistor VR.

Furthermore, the power supply unit NT and the control unit SE are arranged on a printed circuit board LP, which has at least a part of the first and second line [Ti, L12. Furthermore, the measurement connection that is not connected to the output of the power supply unit NT via the pull-up resistor PR is at least partly connected to the measurement resistor MR via a conductor track LB of the printed circuit board LP. In the example, the first measurement connection ME is connected to the input-connection-side connection of the measurement resistor MR via the conductor track [Band the first line [Ti, which can also be embodied as a conductor track of the printed circuit board.

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

Furthermore, a voltage limiting element D1, D2 is connected between the first and second measurement connection. In the example in accordance with figure 2 in the form of (one or) two diodes D1, D2. In the example, said two diodes D1, D2 are connected in anfiparallel for the purpose of voltage limitation.

In the example in accordance with figure 2, the measurement resistor is embodied in the form of a bimetal or bimetal protection element BM, wherein the latter does not have to be located on the printed circuit board LP, as shown in the example. Said bimetal or bimetal protection element is arranged outside of the printed circuit board LP and connected on the output connection side (Al) to a measurement connection via the wire-like connecting line (DVL), in particular to the measurement connection that is connected to the power supply unit NT via the pull-up resistor PR; in the example the second measurement connection MA.

Furthermore, an interruption unit UE is provided to interrupt the low-voltage circuit. Said interruption unit can interrupt the low-voltage circuit in particular in the presence of a wire fracture identification signal. In the example in accordance with figure 2, the interruption unit UE is connected upstream of the input side of the power supply unit NT. The interruption unit -12 -can have contacts for interrupting the first or/and second line LT1, LT2, as indicated in figure 2.

Figure 3 shows an arrangement in accordance with figure 2 with the difference that a bimetal protection element BM is connected in series with the measurement resistor MR. The wire-like connecting line DVL is in this case attached at the connecting point between the measurement resistor MR and the bimetal protection elements BM.

In the example of figure 3, the measurement circuit MS of the control unit SE is implemented using an amplifier AMP to ascertain the magnitude of the current or an equivalent from the voltage drop across the measurement resistor MR.

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

In this case, the measurement resistor MR or/and the bimetal protection element BM can be arranged entirely or partly on the printed circuit board LP.

In one configuration, the control unit SE is configured in such a way that series arcing faults in the low-voltage circuit are identified and an arcing fault identification signal is output when an arcing fault limit value is exceeded, in particular the low-voltage circuit is interrupted by way of the interruption unit UE, which may also be arranged outside of a housing of the protective switching device SG The measurement resistor MR advantageously has a resistance value in the milliohm range. For example, in the range of 1 to 10 or 100 milliohm. The higher the measurement current of the protective switching device, the lower the resistance value of the measurement resistor should be.

The pull-up resistor PR advantageously has a resistance value between 100 ohm and 10 megaohm, in particular between 1 kiloohm and 1 megaohm, more specifically values between 10 kiloohm and 100 kiloohm inclusive or 1 megaohm.

-13 -The pull-up resistor PR advantageously has a resistance value at least 1000 times, in particular 10,000 times, 100,000 times, 1,000,000 times, 10,000,000 times, or 100,000,000 times the resistance value of the measurement resistor MR. The higher the value, the lower the measurement error. On the other hand, a stable potential has to be provided.

The voltage that is output by the power supply unit NT may be 3.3 volts, for example. For example, silicon diodes can be used as voltage limiting element. These usually have a forward voltage of 0.7 volts. When an input voltage at the measurement connections that exceeds a first threshold value is identified, a wire fracture identification signal is output. In this example, said first threshold value can have a magnitude of 0.5 or 0.6 volts. Said first threshold value should be below the voltage limiting value of the voltage limiting element.

In the presence of a wire fraction identification, for example optical (for example LED), electrical (opening/closing of a switching contact) or/and acoustic signaling is effected.

The low-voltage circuit can also be interrupted. A safe state in the circuit is thus produced since there is no monitoring due to the wire fracture.

The invention can advantageously be implemented as a method.

In the following text, the invention is explained once more in other words. A measurement resistor (shunt) is used to measure the current (load current) of the low-voltage circuit. In some cases, the connection to the measurement resistor can be/become damaged. If, for example, the measurement resistor is connected to a wire (wire-like connecting line), the wire can fracture. This type of fault is not identified. In the case of such a fault, the device is not operational/faulty without an identifiable indication.

According to the invention, what is known as a pull-up resistor with a much higher resistance than the measurement resistor is added at the input of the control unit/measurement circuit or current conditioning circuit. When the measurement resistor is connected to the measurement circuit, the effect of the pull-up resistor is negligible. When the connection to the measurement resistor is interrupted, the voltage at the measurement circuit is very high, in accordance with or proportional to the output voltage of the power supply unit (optionally voltage divider with pull-up resistor, that is to say reduced). Said high and constant, in particular DC, voltage can -14 -be detected by the measurement circuit or a microprocessor MCU connected to the output of the measurement circuit.

A wire fracture identification signal can be output.

The measurement resistor may be a bimetal. The measurement circuit could be an analog circuit with resistors, an operational amplifier circuit or a completely integrated conditioning IC, such as an ASIC.

One possible implementation of the invention consists in using it in an arc fault detection device, which identifies series arcing faults. Also in a line circuit breaker or a combined arc fault detection device/line circuit breaker, for example in a housing with a width of 1 TE.

In the case of a pure line circuit breaker, the measurement resistor can be embodied as a bimetal of the line circuit breaker.

In the case of an arc fault detection device function, the control unit or measurement circuit can be configured as an ASIC for arcing fault identification functions including amplification and optionally offset addition.

The invention can also be used for measuring energy. In this case, an amplifier Amp is used. In this case, a precise reference voltage Vref can be generated by the power supply unit and output to the amplifier in order to make precise current measurement possible, which is used for identifying energy quantities. Particularly in this case, in addition to a positive voltage V+, a negative voltage V-can also be provided to the amplifier for the purpose of precise measurement of the negative component of the current/load current. The reference voltage Vref, which, for example, is half of the supply voltage of the power supply unit, is added to the output signal in the amplifier in order to make possible or to improve the measurement by way of the microprocessor MCU.

The invention makes it possible to identify and signal a faulty device. Otherwise, a device would be faulty without indication. This increases the general safety level. The invention can be implemented easily by way of an additional resistor.

-15 -Although the invention has been described and illustrated in detail by way of the exemplary embodiment, the invention is not restricted by the disclosed examples and other variations can be derived herefrom by a person skilled in the art without departing from the scope of protection of the invention as defined by the appended claims.

Claims

-16 -Claims 1. A protective switching device for a low-voltage circuit, in particular for identifying series arcing faults, having: a first input connection (El), which is connected to a first output connection (Al) by way of a first line ([Ti), for a first conductor (L1) of the low-voltage circuit, a second input connection (E2), which is connected to a second output connection (A2) by way of a second line (LT2), for a second conductor (N) of the low-voltage circuit, a measurement resistor (MR), which is inserted in the first or second line ([Ti, LT2), for ascertaining the magnitude of the current of the low-voltage circuit, a power supply unit (NT), the input side of which is connected to the first and second line ([Ti, LT2), for supplying energy to a control unit (SE), in particular for identifying series arcing faults, wherein the control unit (SE) has a first and a second measurement connection, which are connected to the measurement resistor (MR), and wherein the first or second measurement connection is connected to an output of the power supply unit (NT) via a pull-up resistor (PR).
2. The protective switching device as claimed in patent claim 1, wherein the measurement resistor (MR) is connected by way of a wire-like connecting line (DV[) to the measurement connection that is connected to the output of the power supply unit (NT) via the pull-up resistor (PR).
3. The protective switching device as claimed in patent claim 1 or 2, wherein the power supply unit (NT) and the control unit (SE) are arranged on a printed circuit board (LP), which has at least a part of the first and second line (LT1, LT2).
4. The protective switching device as claimed in patent claim 2 or 3, wherein the measurement connection that is not connected to the output of the power supply unit (NT) via the pull-up resistor (PR) is at least partly connected to the measurement resistor (MR) via a conductor track (LB) of the printed circuit board (LP).
5. The protective switching device as claimed in patent claim 1, 2, 3 or 4, wherein the control unit (SE) has a measurement circuit (MS), in particular using an ASIC (ASICA) or an -17 -amplifier (AMP), to ascertain the magnitude of the current or an equivalent from the voltage drop across the measurement resistor (MR).
6. The protective switching device as claimed in one of the preceding patent claims, wherein the control unit (SE) has a microprocessor (MCU).
7. The protective switching device as claimed in one of the preceding patent claims, wherein a voltage limiting element (D1, D2) is connected between the first and second measurement connection, in particular in the form of one or two diodes (D1, 02), wherein, in particular in the case of two diodes (D1, D2), these are connected in antiparallel.
8. The protective switching device as claimed in one of the preceding patent claims, wherein the control unit (SE) is configured in such a way that series arcing faults in the low-voltage circuit are identified and, when an arcing fault limit value is exceeded, an arcing fault identification signal is output, in particular the low-voltage circuit is interrupted.
9. The protective switching device as claimed in one of the preceding patent claims, wherein the pull-up resistor (PR) has a resistance value between 100 ohm and 10 megaohm, in particular between 1 kiloohm and 1 megaohm, more specifically values between 10 kiloohm and 100 kiloohm inclusive.
10. The protective switching device as claimed in one of the preceding patent claims 1 to 8, wherein the pull-up resistor (PR) has a resistance value at least 1000 times, in particular 10,000 times, 100,000 times, 1,000,000 times, 10,000,000 times, or 100,000,000 times the resistance value of the measurement resistor (MR).
11. The protective switching device as claimed in one of the preceding patent claims, wherein the measurement resistor (MR) has a resistance value that is constant at least in a temperature range.
12. The protective switching device as claimed in one of the preceding patent claims, wherein a voltage that is proportional to the current is dropped across the measurement resistor (MR).
-18 - 13. The protective switching device as claimed in one of the preceding patent claims 1 to 10, wherein the measurement resistor (MR) has a bimetal or is a bimetal protection element (BM).
14. The protective switching device as claimed in one of the preceding patent claims 1 to 12, wherein a bimetal protection element (BM) is connected in series with the measurement resistor (MR).
15. The protective switching device as claimed in one of the preceding patent claims, wherein, when an input voltage at the measurement connections that exceeds a first threshold value is identified, a wire fracture identification signal is output, in particular in that optical, electrical or acoustic signaling is effected in the presence of a wire fracture identification signal.
16. The protective switching device as claimed in one of the preceding patent claims 15, wherein an interruption unit (UE) for interrupting the low-voltage circuit is provided, which interrupts the low-voltage circuit in particular in the presence of a wire fracture identification signal.
17. The protective switching device as claimed in one of the preceding patent claims 16, wherein the interruption unit (UE) is connected upstream of the input side of the power supply unit (NT) or/and has contacts for interrupting the first or/and second line.
18. The protective switching device as claimed in one of the preceding patent claims, wherein the low-voltage circuit is a low-voltage AC circuit.
19. The protective switching device as claimed in one of the preceding patent claims, wherein the protective switching device is an arc fault detection device, a line circuit breaker, a circuit breaker or a residual current device or has an arc fault detection, a line detection or a residual current protection functionality.
20. A method for a protective switching device for a low-voltage circuit, in particular for identifying series arcing faults, -19 -in which a current measurement is carried out by means of a measurement resistor (MR), via which the current of a conductor of the low-voltage circuit is conducted, to ascertain the magnitude of the current of the low-voltage circuit, the measurement resistor (MR) is connected to a measurement circuit (MS) by way of at least one wire-like connecting line (DVL), the measurement circuit (MS) is supplied with energy by way of a power supply unit, wherein the connection of the measurement circuit (MS) to which the wire-like connecting line (DVL) is connected is connected to an output of the power supply unit (NT) via a pull-up resistor (PR) such that a fracture in the wire-like connecting line (DVL) can be ascertained by way of a voltage at the input of the measurement circuit (MS) that exceeds a first threshold value and signaled.
21. The method as claimed in patent claim 20, wherein the signaling is effected by way of an optical display, activation of a switching contact or/and interruption of the low-voltage circuit.