Circuit breaker having a mechanical changeover switch and a monitoring device

Abstract

The invention relates to a circuit breaker having a mechanical changeover switch (K1) and a monitoring device (μp), wherein the mechanical changeover switch (K1) has a first terminal (NC), a second terminal (NO) and a third terminal (COM). The circuit breaker has an input terminal (Ein) for applying an operating voltage to the third terminal (COM). The mechanical changeover switch (K1) can assume two connecting states. In a first connecting state of the mechanical changeover switch (K1), the first terminal (NC) is connected to the third terminal (COM) and, in the second connecting state, the second terminal (NO) is connected to the third terminal (COM). The circuit breaker furthermore comprises a measuring circuit (MS) which has a voltage divider and is connected to the first terminal (NC) and to the third terminal (COM) and also to an input (X4) of the monitoring device (μp) for the purposes of providing and monitoring a voltage (UB1) that can be tapped off across the voltage divider. The measuring circuit is furthermore configured such that, depending on the connecting state of the changeover switch (K1), firstly a change in the voltage divider is effected and secondly exactly one of two different voltages is provided at the input (X4) when an operating voltage is applied to the third terminal (COM).

Description

[0001] Circuit breaker with mechanical changeover switch and monitoring device

[0002] Description

[0003] The invention relates to a circuit breaker with a mechanical changeover switch and monitoring device.

[0004] It is known in a wide variety of fields to use electronic circuit breakers, i.e. circuit breakers that comprise at least one electronic switch, hereinafter referred to simply as circuit breakers for the sake of simplicity.

[0005] As the applicant's WO 2019 / 234211 A1 rightly notes, an electrical system with a relay-controlled electrical consumer is known from DE 10 2004 036 252 A1. The relay can be monitored with regard to load current and supply voltage, i.e. with regard to the switched input. DE 10 2014 016 218 A1 discloses a system and method for monitoring relay contacts. In this case, an additional signal emitter is switched on on each side of the switch, and an additional high-frequency signal is evaluated. EP 2 587 512 B1 by the applicant discloses a safety-related switching device with positive guidance. With positive guidance, for example, the normally closed contact and the other contacts, the switching contact and / or a normally open contact, are coupled to one another in such a way that the normally closed contact and the normally open contact cannot be closed at the same time.DE 10 2006 013 329 A1 discloses a method for fault detection in a network system. In this system, a defined voltage potential is applied to a bus branch via an additional switching device to detect the disconnection state of a relay. DE 10 2015 121 194 A1 further discloses a device with an integrated protection circuit, in which the electronic switch is controlled based on a specific current. Galvanically isolating circuit breakers are also used in many areas of electrical systems. These circuit breakers are designed to provide galvanic isolation when the circuit breaker is switched off.

[0006] For this reason, circuit breakers are used, for example, which provide galvanic isolation via a relay using mechanical switches. However, mechanical contacts, such as those used in relays, have the property that the switching contacts can stick or weld together, making reliable galvanic isolation impossible. If the mechanical contact fails, as is particularly the case with a relay, a related problem, such as system failure, can occur.

[0007] If such circuit breakers additionally or alternatively have a purely electronic switch, e.g. a high-performance semiconductor (e.g. IGBT), and the circuit breaker is therefore an electronic circuit breaker within the scope of the invention, this can usually be monitored by a current sensor and also switched off in good time in the event of a short circuit.

[0008] From WO 2019 / 234211 A1 of the applicant, a circuit breaker with a monitoring device is known, which has an electronic switch and a mechanical changeover switch, wherein the mechanical changeover switch in turn has a first terminal, a second terminal and a third terminal, wherein in a rest position of the mechanical changeover switch the first terminal is connected to the third terminal and wherein in an operating position of the mechanical changeover switch the second terminal is connected to the third terminal, wherein the electronic switch is connected to the third terminal of the mechanical changeover switch as a series circuit, wherein when the circuit breaker is switched on in a first switching state the electronic switch is initially activated, wherein at the first terminal the monitoring device is used to measurewhether the first terminal has essentially the same potential as the third terminal and, if so, whether in a subsequent switching state both the electronic switch is activated and the mechanical changeover switch is in the operating position.

[0009] If, using such an electronic circuit breaker, the electronic switch is first activated upon switching on and then the monitoring device checks whether essentially the same potential can be measured at the first terminal as at the third terminal, it can be determined, as described in WO 2019 / 234211 A1, whether the first terminal is correctly connected to the third terminal or whether the second terminal is faultily connected. If, when the circuit breaker is switched off, the mechanical

[0010] If the changeover switch is deactivated so that it is deactivated in a first switching state, and then only by means of the monitoring device is it measured whether essentially the same potential is present at the first terminal as at the third terminal, it can therefore be detected, as similarly described in WO 2019 / 234211 A1, even when switched off, whether the first terminal is correctly connected to the third terminal or whether the second terminal is still faultily connected.

[0011] Therefore, two potential measurements must always be carried out, ie at the first and third connection, and the two measured potentials must be fed separately to the monitoring device via corresponding inputs before a check can be carried out to determine whether galvanic isolation is present or not, ie in particular whether reliable galvanic isolation is no longer possible when the switch is changed due to gluing / welding.

[0012] In particular, WO 2019 / 234211 A1 proposes to query the functionality of the circuit breaker using two voltage dividers, one behind the electronic switch at the third terminal and one at the first terminal. This allows for the detection of, for example, a relay sticking between the second and third terminals. The measured potentials or detected voltage levels are then compared for plausibility using the monitoring device. If unequal levels are reported that do not correspond to the sequence, a fault in the relay can be assumed.

[0013] Even if the solution provided in WO 2019 / 234211 A1 is already fundamentally safe, the object of the present invention is to design a circuit breaker with simpler means without compromising safety.

[0014] The solution according to the invention is provided by a circuit breaker having the features according to claim 1. Preferred embodiments are the subject of the dependent claims.

[0015] According to the invention, a circuit breaker with at least one mechanical changeover switch and a monitoring device is therefore proposed, in which the mechanical changeover switch has a first connection, a second connection and a third connection in a basically known manner, and wherein the circuit breaker has an input connection for applying an operating voltage to the third connection and the mechanical changeover switch can assume two connection states, namely a first connection state in which the first connection is connected to the third connection, and a second connection state in which the second connection is connected to the third connection.

[0016] According to the invention, the circuit breaker is characterized in particular in that it further comprises a measuring circuit with a voltage divider, wherein the measuring circuit is connected to the first terminal and the third terminal, and is connected to an input of the monitoring device for providing and monitoring a voltage that can be tapped off via the voltage divider, and wherein the measuring circuit is further designed such that, depending on the connection state of the changeover switch, on the one hand a change in the voltage divider occurs and, on the other hand, when the operating voltage is applied to the third terminal, exactly one of two different voltages is provided at the input.

[0017] A significant advantage is that only one, in particular a single, voltage needs to be tapped or measured, and consequently, only a single input needs to be provided on the monitoring device through which the voltage tapped for monitoring can be provided. In other words, one input, in particular an analog-digital input, can be eliminated while maintaining the same functionality.

[0018] In a particularly preferred embodiment, the circuit breaker is designed as an electronic circuit breaker and consequently additionally comprises an electronic switch, in particular an electronic switch which is arranged in series between the input terminal and the third terminal.

[0019] Further features and advantages of the invention will become apparent from the following description of preferred embodiments with reference to the accompanying drawings, in which:

[0020] Fig. 1 is a schematic representation of an electrical equivalent circuit according to a particularly preferred embodiment of the invention, and Fig. 2 shows various switching, connection and voltage states in a time sequence to illustrate individual monitoring scenarios of monitoring that can be carried out with preferred embodiments according to the invention.

[0021] Embodiments of a circuit breaker according to the invention with a mechanical changeover switch Kl and a monitoring device pp are described in detail below with reference to the figures, wherein the mechanical changeover switch Kl has a first connection NC, a second connection (NO) and a third connection COM and the circuit breaker has an input connection ON for applying an operating voltage to the third connection COM, and wherein the mechanical changeover switch Kl can assume two connection states, wherein in a first connection state of the mechanical changeover switch Kl the first connection NC is connected to the third connection COM and in the second connection state the second connection (NO) is connected to the third connection COM.As outlined in the figures, the circuit breaker according to the solution according to the invention further comprises a measuring circuit MS with a voltage divider, which is connected to the first terminal NC and the third terminal COM, and with an input X4 of the monitoring device pp, specifically for providing and monitoring a voltage UB1 which can be tapped off via the voltage divider, wherein the measuring circuit is further designed such that, depending on the connection state of the changeover switch Kl, on the one hand a change in the voltage divider occurs and, on the other hand, when the operating voltage is applied to the third terminal COM, exactly one of two different voltages is provided at the input X4.

[0022] However, before referring in detail to the embodiments outlined in the figures below, it should be noted that the words "a", "an" and "one" are only used as pure numerals if this is explicitly indicated, for example by the use of supplementary words such as "merely", "only" or "only one".

[0023] As already explained in WO 2019 / 234211 A1 by the applicant, galvanically isolating circuit breakers are often used, particularly in the process industry, to switch off an output in the event of an overload or short circuit. A particularly preferred, but merely exemplary, embodiment of a circuit breaker according to the invention is shown schematically in Fig. 1 in the form of an electrical equivalent circuit diagram. A circuit breaker according to the invention thus has, according to Fig. 1, at least one mechanical changeover switch K1 and a monitoring device and, in a particularly preferred embodiment, also an electronic switch S2. In Fig. 1, the monitoring device is provided with the reference symbol pp, since a monitoring device usually has a microprocessor for carrying out certain actions, ie in the present case in particular for carrying out monitoring tasks.However, it should be noted that a processor included in the monitoring device does not necessarily have to be a microprocessor and / or that a different type of switching or computing unit, particularly one comprising an integrated circuit, such as a controller, could be used instead of a microprocessor. The electronic switch S2 can, for example, be based on a semiconductor, a switching transistor, such as a field-effect transistor.

[0024] Without limiting its generality, such a circuit breaker basically has an input terminal Ein, via which an input voltage UEin can be provided for the circuit breaker.

[0025] The mechanical changeover switch Kl, e.g. a relay, has a first terminal NC, a second terminal NO and a third terminal COM, whereby an operating voltage UB can be applied to the third terminal COM via the input terminal Ein.

[0026] The mechanical changeover switch Kl can now basically assume two connection states: in a first connection state of the mechanical changeover switch Kl, the first terminal NC is connected to the third terminal COM, and in the second connection state of the mechanical changeover switch Kl, the second terminal NO is connected to the third terminal COM. This means that the changeover switch Kl can be designed as a relay with a changeover contact.

[0027] As outlined in Fig. 1 in a preferred embodiment, the first connection state corresponds to a rest position of the mechanical changeover switch Kl and the second connection state corresponds to an operating position of the mechanical changeover switch Kl. Consequently, according to Fig. 1, when the second connection state is assumed, ie in the operating position, when the second terminal NO is connected to the third terminal COM, an output of the protective switch can be supplied with voltage, in particular with the operating voltage UB.

[0028] In a particularly preferred embodiment, the changeover switch Kl is set up in such a way that the first connection NC functions in particular as a so-called normally closed contact, the second connection NO functions in particular as a so-called normally open contact and the third connection functions in particular as a so-called common contact of the changeover switch.

[0029] If the changeover switch Kl is in the first connection state, shown in Fig. 1 as the rest position, in which the first terminal NC is connected to the third terminal COM, not only is there no operating voltage UB at the Aus output, but the Aus output is also galvanically isolated, i.e., in particular, galvanically isolated from the third terminal COM. In other words, the output can be galvanically isolated in the event of a fault and / or during normal shutdown of the output.

[0030] In the following, for the understanding of the invention, it is assumed that, as can be seen in Fig. 1, for each input On there is only one output Off that can be controlled by the protection switch, ie can be switched on and off, even if, in a modification to Fig. 1, several controllable outputs can in principle be arranged together at one input and can also be operated with one and the same operating voltage UB.

[0031] To control and thus switch the mechanical changeover switch Kl, a control or switching signal can be sent to it, for example via an output X3 of the monitoring device pp, in particular to an activation unit S1 of the changeover switch that can be controlled for this purpose. A control or switching signal sent by the monitoring device pp can thus, in particular, also include or cause the application of a switching or excitation voltage to an excitation coil included in the changeover switch Kl as the activation unit S1.

[0032] The electronic switch S2 provided according to the preferred embodiment is arranged in series between the input connection Ein and the third connection COM of the mechanical changeover switch Kl or is connected by means of a series connection. In this case, a direct sequence or a series connection with further, in particular intermediate components can be provided. Thus, as can be seen in Fig. 1, for example, a current measuring device Imess can be a further intermediate component, via which the current flowing when the electronic switch S2 is activated can be measured and the result can be fed to the monitoring device pp via a connection X2. In this way, for example, the electronic switch S2 can also be monitored with the monitoring device pp and, in particular, switched off in good time in the event of a short circuit, e.g. via connection XI of the monitoring device pp.It is useful for the electronic switch S2 to not only be switched off but also switched on, i.e. activated, via the terminal XI of the monitoring device pp.

[0033] It can also be provided according to Fig. 1 that the input voltage UEin is also available to the monitoring device pp itself directly or indirectly, for example, as shown, the input voltage UEin is connected to a terminal X5 of the monitoring device pp via a voltage divider R5, R6. Via this terminal X5, on the one hand, the supply voltage for the monitoring device pp can be provided and / or the monitoring device pp can expediently detect or monitor whether or that an input voltage UEin is present. Furthermore, a circuit breaker according to the invention according to Fig. 1 can also comprise an operating and display functionality for a user, in particular, as outlined, an operating and display functionality connected to the monitoring device pp, and / or a telecommunications functionality FM, which, for example, as outlined, is connected to the monitoring device pp via a terminal X6 of the latter for interaction therewith.

[0034] According to the solution of the invention, it is now further provided that the protective switch further comprises a measuring circuit MS, which is connected to the first terminal NC and the third terminal COM, and is connected to an input X4 of the monitoring device pp for providing and monitoring a voltage UB1 which can be tapped off via a voltage divider of the measuring circuit MS. The measuring circuit is expediently designed in such a way that, depending on the connection state of the changeover switch Kl, on the one hand, a change in the voltage divider occurs and, on the other hand, when the operating voltage UB is applied to the third terminal COM, exactly one of two different voltages is present at the

[0035] Input X4 is provided

[0036] In order to form the voltage divider, so that a single voltage UB1 which varies depending on the connection state can be tapped and made available to the monitoring device pp via a single input X4 for monitoring there, the measuring circuit MS for this purpose according to Fig. 1 comprises, in a particularly preferred embodiment, at least two series-connected resistance units, e.g. according to Fig. 1, a first resistance unit formed from the resistors RI and R3, and a second resistance unit formed from the resistors R2 and R4, between which a voltage UB1 which varies depending on the connection state can be tapped in the simplest way, ie according to Fig. 1 on the measuring circuit branch Bl. This is because the resistance value changes in at least one of the resistance units depending on the connection state.

[0037] If the measuring circuit MS is connected to the first terminal NC, the third terminal COM and to the input X4 of the monitoring device pp, via which the voltage UB11 that can be tapped or tapped at the voltage divider can then be provided, then, as can be seen from Fig. 1, the first resistance unit formed from the resistors RI and R3 is included between the first and third terminals NC, COM and the input X4 of the monitoring device pp in the measuring circuit.

[0038] In a practical embodiment, the measuring circuit consequently has a first measuring circuit path between the first terminal NC and the input X4 of the monitoring device pp, in which preferably at least one resistor RI is arranged, and a second measuring circuit path between the third terminal COM and the input X4 of the monitoring device pp, in which preferably at least one resistor R3 is likewise arranged.

[0039] In the first connection state of the changeover switch Kl, i.e., when the changeover switch Kl connects the first terminal NC to the third terminal COM, the at least one resistor RI is consequently connected in parallel with the at least one resistor R3. In other words, the resistance value of the first resistance unit formed by the resistors RI and R3 between the first and third terminals NC, COM, and the input X4 of the monitoring device pp in the measuring circuit is in this case based on the resulting resistance value of the parallel-connected resistors RI and R3.

[0040] By contrast, in the second connection state of the changeover switch Kl, i.e., when the changeover switch Kl connects the second terminal NO to the third terminal COM, the at least one resistor R3 arranged in the first measuring circuit path between the first terminal NC and the input X4 of the monitoring device pp is irrelevant for the voltage divider. In other words, the resistance value of the first resistance unit formed from the resistors RI and R3 between the first and third terminals NC, COM, and the input X4 of the monitoring device pp in the measuring circuit is based solely on the resistance value of the resistor RI.

[0041] If no operating voltage UB is present at the third terminal COM, meaning a zero voltage is present at the third terminal COM, the voltage tapped and provided via the voltage divider of the measuring circuit MS is also appropriately equal to zero. However, if the operating voltage UB is present at the third terminal COM, the voltage tapped and provided via the voltage divider of the measuring circuit MS is different depending on whether the first or second connection state has been adopted, and thus a different, clearly identifiable voltage greater than zero.

[0042] In particular, when the operating voltage UB is applied to the third terminal COM, in a practical implementation, the tapped voltage UB1 only needs to be monitored against a single threshold value X (Fig. 2) to determine whether the first or second connection state is assumed when the operating voltage UB is applied, and whether this represents a fault-free or faulty state. Furthermore, the measuring circuit MS is expediently dimensioned such that the tapped voltages are sufficiently separated from each other for reliable detection. Of course, this separation may also vary depending on the design of the monitoring device.

[0043] In particular, this makes it possible to detect without further steps or measures whether galvanic isolation is present or not, ie the effecting or causing of galvanic isolation by the changeover switch Kl can be monitored.

[0044] In particular, in order to enable a more detailed and reliable detection of the functional capability as well as a possible cause of the fault, the monitoring device pp is suitably designed to relate the voltage UB 1 provided at the input (X4) for monitoring purposes to a respective operating state of the protective switch that can currently be detected by the monitoring device.

[0045] Thus, a state when the operating voltage UB is not applied to the third terminal COM preferably corresponds to a first operating state, i.e., an off state. A tapped voltage UB1 in this case is therefore advantageously zero, i.e., particularly during fault-free operation.

[0046] A state with an operating voltage UB applied to the third terminal COM and a control of the mechanical changeover switch Kl to assume the first connection state preferably corresponds to a second operating state, ie a first on state.

[0047] A state with an operating voltage UB applied to the third terminal COM and a control of the mechanical changeover switch Kl to assume the second connection state preferably corresponds to a third operating state, ie a second on state.

[0048] In the embodiment outlined in Fig. 1, it is further apparent that, assuming that an input voltage UEin must first be present so that an operating voltage UB can be applied to the third terminal at all, the second or third operating state can consequently only exist if the electronic switch S2 is also activated. Accordingly, the monitoring device expediently carries out the monitoring, in particular also depending on the input voltage UEin detected at the input terminal Ein, and / or activates or deactivates the electronic switch S2 depending on the monitoring of the voltage UB1 provided at the input X4.This is because, in principle, a voltage UB1 greater than zero can only be present on the measuring circuit branch Bl, or at least should only be present, and therefore a voltage UB1 greater than zero present on the measuring circuit branch Bl can only be measured via the input X4 of the monitoring device pp if an operating voltage UB is present at the third terminal.

[0049] It is also provided in particular that the monitoring device pp carries out the monitoring in an appropriate manner in addition or alternatively depending on an activation of the changeover switch Kl.

[0050] With reference also to Fig. 2, possible monitoring scenarios are described below.

[0051] For a better understanding, however, it is assumed, merely by way of example, that the resistors RI to R4 sketched in Fig. 1 for forming two series-connected resistor units of a voltage divider of the measuring circuit MS are as follows: Rl=10K, R2=1K, R3=1K, R4=10K.

[0052] Furthermore, it is assumed that, when the changeover switch Kl is operating correctly in its rest position, the third terminal COM of the changeover switch Kl is connected to the first terminal NC of the changeover switch Kl, ie in particular its normally closed contact.

[0053] Furthermore, for the implementation of a monitoring procedure outlined below, in particular also within the framework of a monitoring procedure that is expediently carried out at least during the switching on of the circuit breaker, a switching-on process of the circuit breaker is assumed as an example.

[0054] Until a time t1, the electronic switch S2 is not activated, so that during fault-free operation, no operating voltage can be present at the third terminal COM. The voltage UB1 tapped at the measuring circuit branch B1 is therefore zero during fault-free operation.

[0055] When the input voltage is applied, the state of the electronic switch S2 can also be monitored via terminal X2 and / or the functionality of the electronic switch S2 can be tested by activating and deactivating it via terminal XI. At a time t1, the electronic switch S2 is activated. S2 is therefore in the active state during fault-free operation as shown in Fig. 2. During fault-free operation, an operating voltage UB is also present at the third terminal COM when the input voltage UEin is applied.

[0056] If up to time t1 the activation unit S1 of the changeover switch has not been activated according to Fig. 2, i.e. according to Fig. 1 via terminal X3, and the changeover switch is operating correctly, the first terminal NC is connected to the third terminal, i.e. the first terminal NC is essentially in its active operating state (cf. Fig. 2). From time t1 onwards the voltage UB1 tapped at the measuring circuit branch Bl is therefore greater than zero during error-free operation. With the dimensioning of the resistors RI to R4 assumed above a voltage UB1 of 1 / 2 UB is therefore produced at the measuring circuit branch Bl during error-free operation, which voltage is made available to the monitoring device pp via terminal X4 or reported back via this.

[0057] If a fault were to occur, e.g., due to welding of the contacts between the third terminal COM and the second terminal NO, and the first terminal NC were to be exposed and faulty and thus not supply voltage to R3, the measuring circuit MS would be detuned at time t1, and only approximately 1 / 10 of the UB would be available at the measuring circuit branch Bl. In this case, too, the monitoring of the monitoring device would reveal that the voltage provided at input X4 is not related to the respective operating state of the circuit breaker, and the monitoring device pp would thus detect the corresponding fault condition.

[0058] If at time t2 the activation unit S1 of the changeover switch is controlled according to Fig. 2 and the changeover switch is operating correctly, the second terminal NO would be connected to the third terminal COM and the first terminal NC would be disconnected from the third terminal COM, i.e. the first terminal NC would then be in its inactive operating state. However, according to Fig. 2 this has not yet happened, which may indicate a faulty operating state. At time t3 however the contact K1 operates accordingly, albeit somewhat delayed, in accordance with the activation of S1, and the second terminal NO is then connected to the third terminal COM and the first terminal NC is disconnected from the third terminal COM.

[0059] Consequently, at time tl only a voltage UB1 of approximately 1 / 10 UB can be tapped via the measuring circuit MS or at the measuring circuit branch B 1.

[0060] Monitoring is very simple in that, with respect to the changeover switch Kl, only one threshold X needs to be monitored, and this threshold must be related to the operating state of the circuit breaker, particularly depending on the sequence of activation of S1 and S2. If the threshold is above X (as per Fig. 2), a connection is established between the COM and NC terminals when the operating voltage UB is applied, according to the specific dimensioning here. If the threshold is below X, a connection is established between the COM and NO terminals.

[0061] Since only one voltage, i.e. in particular a single voltage, has to be tapped or measured and consequently only a single input has to be provided on the monitoring device via which the voltage tapped for monitoring can be provided, an input on the monitoring device, in particular an analog-digital input, can be saved with the same functionality, in particular compared to WO 2019 / 234211 A1.

[0062] List of reference symbols

[0063] One input of the circuit breaker

[0064] From output of the circuit breaker pp monitoring device

[0065] XI to X4 connections of the monitoring device R5, R6 resistors to form a voltage divider for X5 of the monitoring device

[0066] Small mechanical changeover switch

[0067] S1 controllable activation unit of the changeover switch NC first connection of the changeover switch, in particular Normally-Closed Contact

[0068] NO second connection of the changeover switch, especially Normally-Open Contact

[0069] COM third connection of the changeover switch, in particular common contact of the changeover switch

[0070] FM remote signal S2 switch, electronic

[0071] Imess current measuring device

[0072] UInput voltage

[0073] UB operating voltage

[0074] MS measuring circuit Bl measuring circuit branch

[0075] RI to R4 resistors for forming two series-connected resistor units of a voltage divider of the measuring circuit

[0076] UB1 voltage tapped via the voltage divider on the measuring circuit branch

Claims

Patent claims 1. A circuit breaker with a mechanical changeover switch (Kl) and a monitoring device (pp), wherein the mechanical changeover switch (Kl) has a first terminal (NC), a second terminal (NO), and a third terminal (COM), and wherein the circuit breaker has an input terminal (Ein) for applying an operating voltage to the third terminal (COM), and wherein the mechanical changeover switch (Kl) can assume two connection states, wherein in a first connection state of the mechanical changeover switch (Kl), the first terminal (NC) is connected to the third terminal (COM), and in the second connection state of the mechanical changeover switch (Kl), the second terminal (NO) is connected to the third terminal (COM), wherein the circuit breaker further comprises a measuring circuit (MS) with a voltage divider, wherein the measuring circuit is connected to the first terminal (NC) and the third terminal (COM),and is connected to an input (X4) of the monitoring device (pp) for providing and monitoring a voltage (UB1) which can be tapped off via the voltage divider, and wherein the measuring circuit is further designed such that, depending on the connection state of the changeover switch (Kl), on the one hand, a change in the voltage divider occurs and, on the other hand, when the operating voltage is applied to the third terminal (COM), exactly one of two different voltages is provided at the input (X4).

2. Circuit breaker according to the preceding claim, wherein the first connection state corresponds to a rest position of the mechanical changeover switch (Kl) and the second connection state corresponds to an operating position of the mechanical changeover switch (Kl).

3. Circuit breaker according to one of the preceding claims 1 to 2, wherein the voltage divider comprises two resistor groups (RI, R3; R2, R4) connected in series, wherein the resistance value changes depending on the connection state in at least one of the resistor groups.

4. Circuit breaker according to one of the preceding claims 1 to 3, wherein the monitoring device relates the voltage (UB1) provided at the input (X4) to a respective operating state of the circuit breaker that can currently be detected by means of the monitoring device.

5. Circuit breaker according to the preceding claim 4, wherein a first operating state corresponds to an off state when an operating voltage (UB) is not applied to the third terminal (COM), a second operating state corresponds to a first on state when an operating voltage (UB) is applied to the third terminal (COM) and a control of the mechanical changeover switch (Kl) to assume the first connection state, and a third operating state corresponds to a second on state when an operating voltage (UB) is applied to the third terminal (COM) and a control of the mechanical changeover switch (Kl) to assume the second connection state.

6. Circuit breaker according to one of the preceding claims 4 or 5, wherein, if the monitoring of the monitoring device shows that the voltage (UB1) provided at the input (X4) is not related to the respective operating state of the circuit breaker, the monitoring device (pp) detects a fault condition.

7. Circuit breaker according to one of claims 1 to 6, wherein the monitoring device has at least one connection (X3) via which the mechanical changeover switch (Kl) is connected for activation, and wherein the monitoring device is set up to carry out the monitoring of the voltage (UB1) provided at the input (X4) as a function of activation of the changeover switch (Kl) via this connection.

8. A circuit breaker according to any one of claims 1 to 7, further comprising an electronic switch (S2) arranged in series between the input terminal (In) and the third terminal (COM).

9. Circuit breaker according to claim 8, wherein the monitoring device has at least one terminal (XI) via which the electronic switch (S2) is connected thereto and wherein the monitoring device is configured to activate or deactivate the electronic switch (S2) depending on the monitoring of the voltage (UB1) provided at the input (X4).

10. Circuit breaker according to one of the preceding claims 1 to 9, wherein the monitoring device has at least one terminal (X5) via which an input voltage applied to the input terminal (Ein) can be detected and wherein the monitoring device is set up to monitor the voltage (UB1) provided at the input (X4) as a function of the input voltage detected at the input terminal (Ein).

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