CN110221113A - Apparatus and method for fault current - Google Patents

Abstract

The invention relates to a device for fault currents of low-voltage circuits, having: - a plurality of conductors of the low-voltage circuit, which can be opened or closed by means of contacts, - an interruption unit for opening these contacts, - with the interruption a control unit to which the unit is connected, a summing current transformer whose primary side is formed by the conductors and which has a secondary winding, a detection unit connected to the secondary winding, the detection unit The other hand is connected to the control unit. A selection unit is provided, which is connected to the control unit. The control unit and the selection unit are designed such that it is possible to switch between the fault current circuit breaker function and the fault current monitoring function, so that the device has the function of a fault current circuit breaker or a fault current monitoring device.

Description

Apparatus and method for fault current

technical field

The invention relates to a device for fault currents in low-voltage circuits according to the preamble of patent claim 1, a device for fault currents in low-voltage circuits according to the preamble of patent claim 11 systems and methods.

Background technique

Devices for fault currents are in particular devices for detecting fault currents or differential currents.

Fault current circuit breakers for electrical circuits, in particular for low-voltage circuits or low-voltage systems, are generally known. Fault current circuit breakers are also known as FI circuit breakers or residual current devices RCD for short.

Low voltage means AC voltage up to 1000 volts or/and DC voltage up to 1500 volts. Low voltage means in particular a voltage greater than a small voltage with values of 50 volts alternating current and 120 volts direct current.

Electric circuits, especially low voltage circuits, are circuits for currents up to 6300 Amperes, in particular up to 1600 Amperes, 1200 Amperes, 630 Amperes, 125 Amperes or 63 Amperes. The stated current values refer in particular to the rated current and/or the cut-off current, ie the maximum current which is normally conducted through the circuit or the current which the circuit is normally interrupted by, for example, a protective device such as a circuit breaker or a power switch.

A fault current circuit breaker takes the sum of the currents in the circuit (zero under normal conditions) and responds when it exceeds a differential current value (i.e. exceeds a certain (difference) current value which is a response current value or a fault current value which is a fault response The current sum of current values that are not zero) breaks the circuit.

Almost all fault current circuit breakers to date have a summing current transformer whose primary winding is formed by the conductors of the circuit and whose secondary winding outputs the sum of the currents or the equivalent of the sum of the currents, for example in the form of a voltage, which is directly or Used indirectly to interrupt a circuit.

In addition, two or more conductors, in most cases a reciprocating conductor or an outer conductor and a neutral conductor in a single-phase alternating current network, all three outer conductors or all three outer conductors and the neutral conductor in a three-phase alternating current network The permanent conductors are guided through current transformers which usually have a ring core made of ferromagnetic material. Only the differential current from the conductor is changed, that is to say the current that deviates from the reciprocating current. Usually the sum of the currents in a circuit is equal to zero. The fault current can then be identified.

In this context, fault currents are in question if, for example, the current flows out to ground on the energy consumer side or energy consumer side. A fault situation then exists, for example, when there is an electrical connection of a phase conductor or an outer conductor of the circuit to earth. For example, when a person touches a phase conductor. Part of the current then does not flow back through the neutral or neutral conductor as usual, but through people and earth. This fault current can be measured by means of a summing current transformer, since the sum of the measured values of the outgoing and returning currents is not equal to zero. Interruption of an electrical circuit, eg, at least one conductor, a portion of the conductors, or all conductors, is accomplished by a repeater or retaining magnet release or an interrupting unit (eg, with associated mechanisms). A fault circuit breaker for measuring alternating fault currents is generally known from document DE 44 32 643 A1.

The main function of a fault current circuit breaker is to protect people from electric currents (electric shocks) and to protect systems, machines or buildings from fires caused by electrical insulation failures.

A fault current circuit breaker basically consists of a functional group of summing current transformers, detection units, control units, interruption units/contacts. In addition, a test circuit with a test button and a test resistor is generally provided. The operability of the fault current circuit breaker or fault current protective device can be controlled via the test button.

2-pole version for phase and neutral conductors (L+N), 3-pole version for three phase conductors (L1, L2, L3) and for three phase and neutral conductors (L1, L2 , L3, N) 4-pole fault current circuit breakers are generally known in practice.

There are now so-called monitoring devices/display devices that detect and only display the current. They do not provide protection against circuit interruption. The display devices are of modular construction, they have a housing for the analysis electronics and display, a further housing for the summation current transformer (the two housings are connected to each other via external wires), and an external power supply .

This results in a high space requirement for such devices, since there are many individual components that can be faulty in the wiring. When it is desired to perform both functions in one low voltage circuit or system, installation quickly becomes complicated. There is also the problem that during system operation, especially in systems with frequency converters, it is first desired to obtain a (fault) current and only then to activate the protective function. This has hitherto only been possible in a complex manner.

Contents of the invention

The object of the invention is to provide a compact device for fault currents in low-voltage circuits which has extended functionality.

This object is achieved by a device having the features of patent claim 1 , by a system according to patent claim 14 and by a method according to patent claim 15 .

According to the invention a device (FI) for fault currents of low-voltage circuits is proposed, having:

- multiple conductors of low voltage circuits (multiple conductors means at least two conductors)

- a summing current transformer, the primary side of which is formed by the conductors and which has a secondary winding,

- a detection unit connected to the secondary winding, which detection unit is connected on the other hand to the control unit. The selection unit is set. The selection unit is connected with the control unit. The control unit and the selection unit are configured such that it is possible to switch between a fault current circuit breaker function and a fault current monitoring function, so that the device at least partially provides the function of a fault current circuit breaker or the function of a fault current monitoring device .

This has the particular advantage that the protective and detection functions are integrated in one compact device or housing. In particular, the fault circuit breaker, for example in the form of a module with a switching device, such as a power switch, can be extended with a display/monitoring function. Costs for additional monitoring equipment can be saved. By means of a selection unit, for example in the form of a switch, the user can decide whether he wishes to only "watch" the application without shutting down the application/system in the event of a failure. Alternatively, the device can function as a purely protective device. Alternatively, the two can be combined by, for example, "powering up" a low-voltage circuit/system with a monitoring function or monitoring mode, where only the fault current value is displayed, and then, while the system is operating, switching to Fault current breaker function/breaker mode (fault current protection) such that the circuit is interrupted when a (set) fault current limit value is exceeded. This is advantageous in particular for systems with frequency converters in order to avoid undesired shutdowns due to (technical) leakage currents.

Advantageous developments of the invention are given in the dependent claims.

In an advantageous embodiment of the invention, a first display unit is provided which visually signals the active fault current monitoring function. This has the particular advantage that the user recognizes that "only" the fault current monitoring function is active and that there is no circuit breaker function. This can be done, for example, by lamps, light-emitting diode/LED lamps or the like. The individual states can also be clearly emphasized, for example, by means of reverse text descriptions such as modes.

In an advantageous embodiment of the invention, a second display unit is provided which, when the fault current monitoring function is activated, signals that a fault current limit value has been exceeded. This has the particular advantage that an exceeding of the fault current limit value is indicated when the device is not tripped/protective function is not present. This can likewise be done, for example, by means of lamps, light-emitting diode/LED lamps or the like. Signaling can also take place in the fault circuit breaker function.

In an advantageous embodiment of the invention, a relay or a relay contact output or output is provided, which, when the fault current monitoring function is active, signals that the fault current limit value has been exceeded , specifically by closing (or opening) its relay contacts. This has the particular advantage that, in monitoring mode/monitoring mode, a fault current limit value violation can be signaled or communicated to superordinated units (eg monitoring system, management system, etc.). Signaling can also take place in the fault circuit breaker function.

In an advantageous embodiment of the invention, an interface for an external interrupt unit is provided. This has the particular advantage that, when a fault current limit value is exceeded, the circuit can also be interrupted by an external unit, such as a switching device, for example in the form of a power switch. In this case, the device can be designed, for example, as a module so that it is connected to a switching device, in particular a power switch. The interface can be designed as an electrical interface, for example via an electrical conductor, such as a twisted pair, or (and) via a mechanical interface, for example in the form of a push rod, which is actuated, for example, via a tripping magnet. The enabling plunger trips a switching device, such as a power switch, for example by opening contacts, ie interrupts the circuit.

In an advantageous embodiment of the invention, a power adapter is provided which is connected to at least some of the conductors. This has the particular advantage that there is a power supply integrated in the device, so that the actual outlay on external power adapters and wiring can be dispensed with.

In an advantageous embodiment of the invention, the control unit has a microprocessor. This has the special advantage that there is a particularly simple and flexible implementation of the control unit.

In an advantageous embodiment of the invention, the control unit has an analog-to-digital converter. This has the particular advantage that the detected fault current values (=difference current values) can be easily digitally processed.

In an advantageous embodiment of the invention, the detection unit has a low-pass filter and/or an amplifier. This has the particular advantage that a signal processing of the detected fault current by the summing current transformer is possible. Especially matching and filtering, for example in order to be able to analyze frequency selectively.

In an advantageous embodiment of the invention, the selection unit has a slide switch, a rotary switch or a key switch. This has the particular advantage that there is a particularly simple switching possibility and, in addition, the selected operating mode of the device can be displayed.

In an advantageous embodiment of the invention, the device has contacts which can open or close the conductors of the circuit (current-free or current-carrying). Furthermore, an interruption unit is provided for opening the contacts, which is connected to the control unit. This has the particular advantage of providing a compact device for fault currents which interrupts the circuit when the fault current exceeds a fault current limit value when the fault current circuit breaker function is switched on or activated. In an advantageous refinement of the invention, the device is designed as a module so that it can be connected to a switching device, in particular a power switch. This has the particular advantage that a device such as a power switch can be extended with a fault circuit breaker function or a fault current monitoring function, both functions being provided with little effort.

In an advantageous embodiment of the modular design of the device, the device has a mechanical push rod which is activated when the fault current circuit breaker function is switched on if a fault current limit value is exceeded. This has the particular advantage that it allows particularly simple tripping of connected switching devices, such as power switchers. The plunger can here be part of an interface for an external interruption unit.

According to the invention, a system is also claimed which has a device for fault currents connected to a switching device, in particular a power switcher. Two devices are effectively connected at runtime.

A corresponding method is also claimed according to the invention for a device for fault currents of a low-voltage circuit having a plurality of conductors, wherein a detection circuit is provided for obtaining a differential current of these conductors. Choose between monitoring functions or protection functions. In the case of a monitoring function, the monitoring function is signaled at the device. In the case of a protective function, at least the interruption of the low-voltage circuit is signaled when a differential current threshold is exceeded. That is to say, in an advantageous embodiment of the modular configuration of the device, the information for interrupting the circuit is provided. This can be achieved, for example, by an interface in the form of a mechanical push rod or/and an output or a repeater contact. In the case of a compact design, for example, of devices with integrated contacts, low-voltage circuits can be interrupted directly.

All configurations, whether referring to patent claims 1 or 11 in dependent form or only to individual features or combinations of features of the patent claims, enable an expansion of the functionality of the device for fault currents.

The characteristics, features and advantages of the invention as described, as well as its implementation, will become clearer and easier to understand in conjunction with the following description of the embodiments explained in detail in conjunction with the accompanying drawings.

Description of drawings

The accompanying drawings show:

Figure 1 shows a first block diagram of the device for fault current,

Figure 2 shows a second block diagram of the device for fault current,

Figure 3 shows a third block diagram of the device for fault current,

Figure 4 shows a fourth block diagram of the device for fault current,

Figure 5 shows a first view of the device for fault current,

Figure 6 shows a second view of the device for fault current,

Figure 7 shows a third view of the device for fault current,

Figure 8 shows a fourth view of the device for fault current,

FIG. 9 shows a fifth block diagram with a device for fault currents.

Detailed ways

Figure 1 shows a first block diagram of a device for fault currents of low-voltage circuits, which has:

- a plurality of input terminals 1, 3, 5, NE for connecting the device for the fault current FI to an energy source, such as a low-voltage circuit or a low-voltage network, on the energy source side;

- a plurality of output terminals 2, 4, 6, NA for connecting the device for the fault current FI to an energy consumer, for example an energy consumer, on the energy consumption side;

- a plurality of conductors L1, L2, L3, N of the low-voltage circuit to be protected, wherein the first conductor L1 is connected between the first input terminal 1 and the first output terminal 2, as above, and the second conductor L2 is connected at the second input Between the terminal 3 and the second output terminal 4, the third conductor L3 is connected between the third input terminal 5 and the third output terminal 6, and the fourth conductor N, such as a neutral conductor, is connected between the fourth input terminal NE and the first Between the four output terminals NA;

- wherein eg the first to third conductors L1, L2, L3 are phase conductors of eg a three-phase AC circuit, and the fourth conductor N is a neutral or neutral conductor;

- a plurality of eg first to fourth contacts K1 , K2 , K3 , KN, by means of which contacts the first to fourth conductors L1 , L2 , L3 , N can be opened or closed, wherein one contact is assigned to one conductor;

- an interruption unit 30 connected to these contacts K1 , K2 , K3 , KN for opening (and closing when appropriate) the contacts K1 , K2 , K3 , KN;

- a control unit 20 connected to an interruption unit 30 which, when appropriate, enables the opening of the contacts K1, K2, K3, KN;

- summation current transformer ZCT, the primary side of this first summation current transformer is formed by these conductors L1, L2, L3, N, wherein these conductors pass through summation current transformer ZCT, and this summation current transformer is for example embodied for example by A toroidal core of ferromagnetic or nanocrystalline material and having a secondary winding, for example with multiple windings, as shown;

- a detection unit 80 connected to the secondary winding, which detection unit is connected to the control unit 20 on the other hand, a selection unit 40 is provided. The selection unit 40 is connected to the control unit 20 . The selection unit 40 and the control unit 20 are designed such that it is possible to switch between the fault current circuit breaker function and the fault current monitoring function, so that the device has the function of a fault current circuit breaker or a fault current monitoring device.

The fault current circuit breaker function refers to the function of the fault current circuit breaker to interrupt the low-voltage circuit when the fault current limit value (=difference current limit value) is exceeded or to signal interruption.

The fault current monitoring function refers to the function of displaying equipment (such as a monitoring device) to obtain a fault current and display the magnitude of the fault current. A protective function like a fault current circuit breaker is not provided at this time.

Under the fault current circuit breaker function, the fault current induced in the secondary winding (for example, exceeding the fault current (limit) value) functionally produces the interruption of at least one conductor, a part of the conductors or all conductors, that is, one, a part or The opening of all contacts interrupts the circuit. Interruption may be assisted by mechanical means not shown.

The control unit 20 may include other units, such as one or more analog-to-digital converters 21 , a value calculation unit 22 or/and a threshold comparison unit 24 . In addition, there is a monitoring unit 23 for identifying the activation of the fault current monitoring function and, if applicable, other monitoring functions. The signal of the selection unit 40 is sent to this monitoring unit 23 . The monitoring takes place depending on the selection of the function, in which disconnection of the circuit is prevented, that is to say the threshold comparison unit 24 receives a signal from the monitoring unit 23 so that no tripping takes place. Otherwise, by means of the signal flow from the secondary winding through the monitoring unit 80, the control unit 20 to the interrupting unit 30, exceeding the fault current (limit) value causes the circuit to be interrupted; and the threshold comparison unit 24 .

The selection unit 40 can, for example, have a slide switch, a rotary switch, a key switch or other switches for selecting functions of the device.

The first display unit 50 is connected to the control unit 20 . The first display unit is embodied, for example, as an optical indicator with light-emitting diodes (LEDs), lamps, displays or the like. It is used for optically, especially actively visually, displaying detection functions. For example via red or green light-emitting diodes.

The second display unit 60 is connected to the control unit 20 . The second display unit is embodied, for example, as an optical indicator with light-emitting diodes (LEDs), lamps, displays or the like. It is used to optically, in particular actively visually, indicate that a fault current (limit) value has been exceeded. For example via yellow light-emitting diodes.

A repeater 70 or a relay unit or circuit output may be provided which, when the fault current monitoring function is activated, signals an exceeding of a fault current limit value. For example, an external voltage source and, for example, a lamp can be used for trip notification.

An interface 10 for an external interrupt unit can be provided. Advantageously, signal indication information can be placed at the interface at all times, ie even when the fault current monitoring function is active, for example when a fault current (limit) value is exceeded. In contrast to the internal interruption unit, the internal interruption unit only receives a signal and subsequently interrupts the circuit when the fault current circuit breaker function is activated.

In addition, a power adapter 90 may be provided, for example a switching power adapter, which is connected to at least some of these conductors, in particular to the first to fourth conductors L1 , L2 , L3 , N. The power adapter is used to supply energy to at least some of the units of the device, such as the control unit 20 or the detection unit 80 .

Functionally, the control unit 20 recognizes the state of the selection unit 40 . The monitoring unit 80 is designed to distinguish different fault currents. When the fault current monitoring function has been selected, for example the first display unit 50 is controlled and the monitoring function is signaled, for example by lighting an LED. This distinguishes the case where there is no protective function but "mere" monitoring. If a fault current limit value is exceeded during the fault current monitoring function, actuation of the second display unit 60 takes place if appropriate. The second display unit signals, for example by means of an illuminated LED, that a fault current limit value has been exceeded. Parallel to this, the interface 10 for the external interruption unit is enabled, if appropriate, so that the circuit can be interrupted externally. The internal interrupt unit 30 is not enabled here.

If the fault current circuit breaker function is activated, both the internal interruption unit 30 and the interface 10 for the external interruption unit are activated when the fault current limit value is exceeded.

The second display unit 60 and the relay unit 70 can also be used for so-called early warnings/"Pre-Alarms". This makes it possible to signal an increase in the fault current or reaching a fault current pre-limit value.

FIG. 2 shows the block diagram according to FIG. 1 with the difference that all functional units, except the interruption unit 30 with contacts K1 , K2 , K3 , KN, are arranged in a housing 200 . The housing 200 can be configured as a module so that it is connected to a switching device, such as a power switch. The connection takes place here via an electrical connection 230 and/or a mechanical connection, for example in the form of a push rod.

Interrupt unit 30 , which includes contacts K1 , K2 , K3 , KN and possibly further units, is here part of a switching device, such as a power switch.

A power switcher here refers to a protection device, similar to the function of a fuse. The power switch monitors the current flowing through it by means of at least one conductor and interrupts the current or energy flow to the energy sink or consumer when a protection parameter such as a current limit value or a current time interval limit value is exceeded, i.e. when When there is a current value for a certain time interval, this is called tripping. The interruption takes place, for example, by opening the contacts of the power switch.

Especially for low voltage circuits or power grids, there are different types of power switchers depending on the magnitude of the current supplied in the circuit. A power switch in the sense of the invention is in particular a switch as used in low-voltage installations with a current of 63 to 6300 amperes. More specifically, closed circuit breakers (geschlossene Leistungsschalter) are used for currents of 63 to 1600 amperes, especially 125 to 630 or 1200 amperes. Especially for currents of 630 to 6300 amperes, more specifically 1200 to 6300 amperes, an open circuit breaker is used. Open circuit breaker (offene Leistungsschalter) is also called air circuit breaker (Air Circuit Breaker), abbreviated as ACB, closed circuit breaker is also called molded case circuit breaker (MouldedCase Circuit Breaker) or compact circuit breaker, abbreviated as MCCB.

A power switch in the sense of the present invention refers in particular to a power switch with an electronic trip unit, also known as an electronic trip unit (ETU for short).

The device for the fault current according to FIG. 2 is connected to a switching device, such as a power switch, wherein the device is designed as a module.

FIG. 3 shows the embodiment according to FIG. 1 with the following differences.

The control unit 20 has only one microprocessor MCU. The microprocessor can, for example, have an integrated analog-to-digital converter at its input AI.

The power adapter 90 has a plurality of units. On the one hand is a DC rectifier unit 91 , followed by a DC voltage converter 92 (such as a DC-DC converter 92 ), followed by a DC voltage regulator 93 (such as a low dropout voltage regulator or LDO). The output of this power adapter 90 provides a supply voltage VCC capable of supplying the control unit 20 as well as other units or circuit components, such as the first and/or second display unit 50 , 60 .

The first and/or second display unit 50, 60 can be implemented, for example, as a series circuit of light-emitting diodes and resistors, which is connected to the output terminal DO of the control unit 20 on the one hand and to the supply voltage VCC of the power adapter 90 on the other hand. connected.

The interruption unit 30 can have, for example, a coil or a relay, by means of which the contacts K1 , K2 , K3 , KN are opened.

The interface 10 for the external interruption unit can, for example, likewise be designed as a repeater, for example, wherein its contacts are provided for connection/as output.

Filters and amplifiers may be included in the detection unit 80, for example operational amplifiers may be used. The filter/low-pass filter can likewise be realized by means of an operational amplifier. The detection unit 80 may have a resistance, as shown.

The detection unit 80 can be configured, depending on the device, for detecting different fault currents, such as purely sinusoidal AC fault currents, pulse-shaped AC fault currents, AC fault currents up to different frequency ranges, pulse-shaped DC fault currents, flat DC fault current and so on.

FIG. 4 shows the block diagram according to FIG. 3 , with the difference that, except for the contacts K1 , K2 , K3 , KN, all units are arranged in a housing 300 . The housing 300 can be designed as a module, which is connected to a switching device 400 , such as a power switch. The connection here takes place, for example, via a mechanical connection 330 , for example in the form of a push rod. The push rod is operated, for example, by means of a coil in the interruption unit 30 . Contacts K1 , K2 , K3 , KN and, if necessary, further units are part of a switching device 400 , such as a power switch, here. The push rod releases the contacts of the switching device 400 , in particular of the power switcher. The switchgear can have other units, such as a mechanism not shown, for moving a push rod for tripping. Alternatively, electrical tripping can also take place, for example by means of an electronic trip unit of a switching device, for example a power switch.

FIG. 5 shows a first exemplary view of a device for a fault current FI according to the present embodiment. In addition to setting possibilities for the fault current, ie the measured fault response current 41 , and/or the tripping time, ie the limit non-response time 42 , the device also has a selection unit 40 , for example in the form of a slide switch. This allows switching between the fault current circuit breaker function and the fault current monitoring function. Also integrated at the surface of the housing of the device are first, second and third display units 50 , 60 , 100 in the form of light emitting diodes. The device according to FIG. 5 is designed here as a module, which can be connected to a switching device.

FIG. 6 is a second exemplary illustration according to FIG. 3 , with the difference that the selection unit 40 has a rotary switch by means of which it is possible to switch between the fault current circuit breaker function and the fault current monitoring function. In addition, different types of fault current identification can be selected, both for the circuit breaker function and for the monitoring function.

FIG. 7 shows a system arrangement with devices for fault currents which are connected in a modular manner 300 to a switching device 400 , for example a power switch.

FIG. 8 shows a further diagram according to FIG. 7, in which the switching output X1 of the repeater 7 is connected to a series circuit of a voltage source U, a fuse F and a first lamp or light-emitting diode L1, optionally with a second A parallel circuit of two lamps or LEDs L2 is connected. For example, an exceeding of a fault current limit value can thus be signaled.

Fig. 9 shows the arrangement of a further system with a device for fault current 500, with an external summing current transformer ZCT; The unit 700 is connected for tripping the switchgear. Unit 700 can be, for example, an electrical overvoltage release or undervoltage release. A device for the fault current 500 can be installed on the support rail 600 , which can have all the units in the housing 200 according to FIG. 2 except for the summation current transformer ZCT.

An advantage of the invention is that a compact device for fault currents is provided which offers extended functionality. Thus, especially when starting a system (in particular with a frequency converter), a rapid start-up can be carried out with little effort by first detecting the fault current in monitoring mode and then protecting the fault current in protection mode with adapted parameters. system.

Furthermore, by means of the invention, the variety of types of fault current circuit breakers and monitoring devices can be reduced, which reduces development, production and inventory costs.

In a compact housing, such as that of a fault circuit breaker, a monitoring function is additionally integrated, which receives its energy supply from the conductors of the circuit. By means of switching, the user can decide whether he can only "observe" the application and should not shut down the system in the event of a fault, or whether the device acts as a purely protective device.

The two cases can be combined by, for example, switching on the system in monitoring mode and switching to protection mode during operation.

Although the invention has been shown and described in detail by the examples, the invention is not limited to the disclosed examples and other variations can be derived by those skilled in the art without departing from the scope of the invention.

Claims (16)

1. An apparatus (FI) for fault currents of low-voltage circuits, having: - a plurality of conductors (L1, L2, L3, N) of the low-voltage circuit, - a summing current transformer (ZCT) whose primary side is formed by these conductors (L1, L2, L3, N), and which The summing current transformer has a secondary winding, - a detection unit (80) connected to the secondary winding, which on the other hand is connected to the control unit (20), It is characterized in that, provided with a selection unit (40), The selection unit is connected to the control unit (20), The control unit (20) and the selection unit (40) are configured as, Switching between a fault current circuit breaker function and a fault current monitoring function is enabled such that the device provides either the function of a fault current circuit breaker or the function of a fault current monitoring device. 2. The device (FI) according to patent claim 1, It is characterized in that, A first display unit (50) is provided, which visually signals the active fault current monitoring function. 3. The device (FI) according to one of the preceding patent claims, It is characterized in that, A second display unit (60) is provided which, if the fault current monitoring function is activated, signals that a fault current limit value has been exceeded. 4. The device (FI) according to one of the preceding patent claims, It is characterized in that, A relay (70) is provided which, when the fault current monitoring function is activated, signals an exceeding of a fault current limit value, in particular by closing its relay contacts. 5. The device (FI) according to one of the preceding patent claims, It is characterized in that, An interface (10) is provided for an external interruption unit, in particular a switching device. 6. The device (FI) according to one of the preceding patent claims, It is characterized in that, A power adapter (90) is provided, which is connected to at least some of the conductors (L1, L2, L3, N). 7. The device (FI) according to one of the preceding patent claims, It is characterized in that, The control unit (20) has a microprocessor (MCU). 8. The device (FI) according to one of the preceding patent claims, It is characterized in that, The control unit (20) has an analog-to-digital converter (21). 9. The device (FI) according to one of the preceding patent claims, It is characterized in that, The detection unit (80) has a low-pass filter and/or an amplifier. 10. The device (FI) according to one of the preceding patent claims, It is characterized in that, The selection unit (40) has a slide switch, a rotary switch or a key switch. 11. The device (FI) according to one of the preceding patent claims, It is characterized in that, This conductor can be opened or closed via contacts (K1, K2, K3, KN), An interrupt unit (30) is provided for opening these contacts (K1, K2, K3, KN), The interruption unit (30) is connected with the control unit (20). 12. The device (FI) according to one of the above patent claims 1 to 10, It is characterized in that, The device is designed as a module so that it can be connected to switching devices, in particular power switches. 13. The device (FI) according to patent claim 12, It is characterized in that, The device has a mechanical pusher that is activated in case of exceeding the fault current limit value when switching on the fault current circuit breaker function. 14. A system with a device according to one of patent claims 1 to 10, 12 or 13, which is operatively connected to a switching device, in particular a power switcher. 15. A method for an installation (FI) of a fault current of a low-voltage circuit having a plurality of conductors (L1, L2, L3, N), wherein a detection circuit for obtaining a differential current of these conductors is provided, It is characterized by: - choice in terms of monitoring functions or protection functions, - in the case of a monitoring function, signaling the monitoring function at the device, - In the case of a protection function, signaling interruption of the low voltage circuit when a differential current threshold is exceeded. 16. The method according to patent claim 15, It is characterized in that, In the case of a monitoring function and when a differential current threshold is exceeded, this is signaled at the device.