TECHNICAL FIELD

The invention relates to a residual current breaker, which comprises first terminals provided for being connected to a phase, a first conductor connecting said first terminals, second terminals provided for being connected to a neutral line and a second conductor connecting said second terminals. Moreover, the residual current breaker comprises a first current sensor, which is provided to measure a total current, comprising a first current through the first conductor and a second current through the second conductor via a magnetic field caused by said total current, wherein the first current sensor is designed to output a first current signal corresponding to said total current. Additionally, the residual current breaker comprises a switch being arranged in the first conductor. In detail, a first switching contact of the switch is arranged in the first conductor. Further on, the residual current breaker comprises a trigger unit, the input of which is connected to the first current sensor and the output of which is coupled to a control input of the switch, wherein the trigger unit causes the switch being opened if the total current, in detail if an AC part of the total current, exceeds an AC switching threshold. Moreover, the invention relates to an electric network, which comprises a main residual current breaker, branched electric lines connected to the main residual current breaker and a plurality of downstream residual current breakers, each being connected to one of the branched electric lines. The main residual current breaker is embodied like the residual current breaker as defined above.

BACKGROUND ART

A device and an electric network of the above kind are generally known in prior art. In case of a ground fault downstream of the residual current breaker, a balance between currents flowing through the residual current breaker is disturbed and a fault current, which corresponds to the aforementioned total current, can be detected at the first current sensor. If the fault current or total current exceeds an AC switching threshold, the trigger unit causes the switch disconnecting the electric network downstream of the residual current breaker from the grid as is known per se. It can happen, that the fault current or total current does not only have an AC part but alternatively or in addition a DC part, for example when DC loads like for example electric cars have an isolation fault. If this DC part gets too high, the first current sensor can saturate what means that the current signal output by the first current sensor does not longer correspond to the real fault current or total current. In other words, the residual current breaker can get “blind”. Accordingly, the switch is not reliably opened when the total current exceeds an AC switching threshold what can lead to dangerous and even to lethal situations.

For this reason, residual current breakers of the type B have been proposed, which in addition to AC residual currents and pulsating DC residual currents also detect smooth DC residual currents. A type B RCD trips in case of AC and/or DC fault currents greater than e.g., 30 mA. In addition, residual current breakers of the type A- EV have been proposed, which are optimized for charging electric cars and which already trip at DC residual currents of > 6 mA.

A drawback of this known solutions is that they are technically complex and comparable expensive. This is particularly disadvantageous in case of hierarchical electric networks, where a residual current breaker upstream of a couple of downstream residual current breakers must handle DC faults, even if DC faults can occur in just one of the downstream branches. It is also to be noted that comparably small and non-dangerous DC fault currents in the branches may sum up to a dangerous DC fault current in the main residual current breaker. One further drawback of prior art networks is that the main residual current breaker cuts off all downstream residual current breakers in case of a DC fault although, for example, not all downstream networks are prone to DC faults at all. Further on, because the upstream residual current breaker must also be designed for the total load current of all downstream branches, such a solution is very expensive.

DISCLOSURE OF INVENTION

Accordingly, an object of the invention is the provision of an improved residual current breaker and the provision of an improved electric network. In particular, a simple solution shall be provided, which avoids saturation of the first current sensor so that the residual current breaker reliably cuts off the current at a defined AC switching threshold. In addition, technical complexity of and costs for hierarchical electric networks, where a residual current breaker upstream of a couple of downstream branches must handle DC faults, shall be reduced.

The object of the invention is solved by a residual current breaker of the type disclosed in the opening paragraph, which additionally comprises a DC current source and a control unit, wherein the DC current source is designed to output a DC compensation current, wherein the total current measured by the first current sensor in addition comprises the DC compensation current (in particular the total current can equal the sum of the first current through the first conductor, the second current through the second conductor and the DC compensation current through the third conductor), the input of the control unit is connected a) to the first current sensor or b) to a second current sensor, wherein the second current sensor is provided to measure said total current, too, and wherein the second current sensor is designed to output a second current signal corresponding to said total current, the output of the control unit is connected to a control input of the DC current source, and the control unit is designed to control the DC compensation current output by the DC current source and the control unit is designed to cause the DC compensation current to flow in opposite direction to a sum of a DC part of the first current and a DC part of the second current and to reduce a magnetic flux caused by a DC part of the total current by use of the first current signal in case a) and by use of the second current signal in case b).

In addition, the object of the invention is solved by an electric network, which comprises a main residual current breaker, branched electric lines connected to the main residual current breaker and a plurality of downstream residual current breakers, each being connected to one of the branched electric lines, wherein the main residual current breaker is embodied like the residual current breaker as defined above. In particular, at least one of the downstream residual current breakers can be embodied as a combined AC/DC residual current breaker and in particular the downstream residual current breakers may also have main circuit breaker functionality, i.e. may open in case of excessive load currents. By use of these measures, the control unit causes the DC current source outputting the DC compensation current, which in best case corresponds to a DC part of the sum of the first current and the second current . Accordingly, there is no effective DC part of the total current any longer. Hence, there is no risk for saturation of the first current sensor and the second current sensor any longer, and the switch is reliably opened when the total current exceeds an AC switching threshold. Accordingly, dangerous and even lethal situations are avoided. It should be noted in this context that the DC compensation current does not need to correspond to a DC part of the sum of the first current and the second current, but a weakened effect is also obtained if the DC compensation current deviates from the DC part of the sum of the first current and the second current.

In other words, the proposed residual current breaker comprises a control loop with the DC current source and the control unit, wherein the DC compensation current is the set value, wherein a DC part of the total current is the measured value and wherein in particular zero can be the target value.

One further advantage is that hierarchical electric networks can be made cheaper because the disclosed residual current breaker upstream of a couple of downstream residual current breakers does not necessarily have to handle DC faults, even if DC faults can occur in the downstream branches. Furthermore, comparably small and non-dangerous DC fault currents in the branches, which are summed up, do not cause a malfunction of the main residual current breaker. Further on, the main residual current breaker does not cut off all downstream residual current breakers in case of a DC fault what is advantageous if a number of downstream networks are not prone to DC faults at all.

It should be noted that there may also be more than one first conductor. For example, the first terminals can be provided for being connected to a plurality of phases and for each phase a first conductor can be provided, the current trough which contributes to the total current. In that the proposed residual current breaker also supports multi-phase systems.

It should be noted that the switch may comprise a plurality of first switching contacts, each being arranged in one of the first conductors. In this way, the residual current breaker can cut off power in all phases in case of a ground fault. In addition, the switch may also comprise a second switching contact in the second conductor. In this way, the residual current breaker can also cut off the neutral line in case of a ground fault.

Further on, it should be noted that the disclosed residual current breaker additionally may also have main circuit breaker functionality, i.e. may open in case of excessive load currents.

Further advantageous embodiments are disclosed in the claims and in the description as well as in the figures.

Advantageously i) the DC current source can be connected to the first conductor at two connecting points with the first current sensor and in case b) additionally the second current sensor in-between, wherein the first conductor then carries the first current and the DC compensation current at the first current sensor and in case b) additionally at the second current sensor, or ii) the DC current source can be connected to the second conductor at two connecting points with the first current sensor and in case b) additionally the second current sensor in-between, wherein second conductor then carries the second current and the DC compensation current at the first current sensor and in case b) additionally at the second current sensor, or iii) the residual current breaker can comprise a third conductor, which connects poles of the DC current source and which runs in parallel with the first conductor and the second conductor at the first current sensor and in case b) additionally at the second current sensor and which (solely) carries the DC compensation current. These are three possible embodiments to bring the DC compensation current to the first current sensor and in case b) additionally at the second current sensor. In case i) the first conductor is used for this reason, in case ii) the second conductor is used for this reason and in case iii) a separate third conductor is used for this reason.

Beneficially, the first current sensor can comprise a first magnetic core, which surrounds the first conductor(s) and the second conductor and which in case iii) additionally surrounds the third conductor, wherein the first magnetic core is designed to guide the magnetic flux caused by said total current and wherein the control unit is designed to cause the DC compensation current to reduce a magnetic flux through the first magnetic core, which is caused by the DC part of the total current. In particular, the first current sensor can comprise a first coil, which is wound around the first magnetic core and which is designed to output the first current signal or can comprise a first magnetic field sensor, which is arranged in the first magnetic core (in particular in a gap of the first magnetic core) and which is designed to output the first current signal. On the one hand, current sensors, which are based on a first magnetic core are reliable means to measure the total current. On the other hand, the inventive problem, i.e. saturation of the first current sensor, is particularly visible when a first magnetic core is used because this first magnetic core can easily get saturated in case of a DC part in the total current. Hence, the proposed solution is particularly useful for these kind of first current sensors.

Beneficially, the second current sensor in case b) can comprise a second magnetic core, which surrounds the first conductor(s) and the second conductor and which in case iii) additionally surrounds the third conductor, wherein the second magnetic core is designed to guide the magnetic flux caused by said total current and wherein the control unit is designed to cause the DC compensation current to reduce magnetic fluxes through the first magnetic core and the second magnetic core, which are caused by the DC part of the total current. In particular, the second current sensor can comprise a second coil, which is wound around the second magnetic core and which is designed to output the second current signal or can comprise a second magnetic field sensor, which is arranged in the second magnetic core, in particular in a gap of the second magnetic core and which is designed to output the second current signal.

The considerations made for the above first current sensor equally apply to the second current sensor. On the one hand, second current sensors, which are based on a second magnetic core are reliable means to measure the total current. On the other hand, the inventive problem, i.e. saturation of the second current sensor, is particularly visible when a second magnetic core is used because this second magnetic core can easily get saturated in case of a DC part in the total current. Hence, the proposed solution is particularly useful for these kind of second current sensors. In an alternative embodiment, the second current sensor can comprise a second coil, which is wound around the first magnetic core and which is designed to output the second current signal or can comprise a second magnetic field sensor, which is arranged in the first magnetic core (in particular in a gap of the first magnetic core) and which is designed to output the second current signal. By use of these measures the first magnetic core provides a double function and a separate second magnetic core can be saved. Nevertheless, the residual current breaker comprises a separate first and second current sensor.

Advantageously, the input of the trigger unit can be connected to the second current sensor, wherein the trigger unit causes the switch being opened if the total current exceeds a DC switching threshold. In this way, the residual current breaker also protects from dangerous DC fault currents. For example, this DC switching threshold can be set to 50 mA.

In an alternative embodiment, the residual current breaker comprises a second trigger unit, the input of which is connected to the second current sensor and the output of which is coupled to a control input of the switch, wherein the second trigger unit causes the switch being opened if the total current exceeds a DC switching threshold. In this way, an alternative possibility to cut off dangerous DC fault currents is proposed. For example, this DC switching threshold can be set to 50 mA, too.

BRIEF DESCRIPTION OF DRAWINGS

The invention now is described in more detail hereinafter with reference to particular embodiments, which the invention however is not limited to.

Fig. 1 shows a schematic circuit diagram of a first example of a residual current breaker;

Fig. 2 shows a schematic circuit diagram of another example of a residual current breaker with the second coil of the second current sensor being wound around the first magnetic core;

Fig. 3 shows a schematic circuit diagram of another example of a residual current breaker with the control unit being connected to the first current sensor; Fig. 4 shows a schematic circuit diagram of further example of a residual current breaker with magnetic field sensors;

Fig. 5 shows a schematic circuit diagram of another example of a residual current breaker with the trigger unit being connected to the second current sensor;

Fig. 6 shows a schematic circuit diagram of further example of a residual current breaker with a second trigger unit;

Fig. 7 shows a schematic circuit diagram of further example of a residual current breaker with a multi pole switch;

Fig. 8 shows a schematic circuit diagram of another example of a residual current breaker with the first conductor carrying the DC compensation current;

Fig. 9 shows a schematic circuit diagram of another example of a residual current breaker with the second conductor carrying the DC compensation current and

Fig. 10 shows a schematic circuit diagram of an electric network with the proposed residual current breaker.

DETAILED DESCRIPTION

Generally, same parts or similar parts are denoted with the same/similar names and reference signs. The features disclosed in the description apply to parts with the same/similar names respectively same/similar reference signs. Indicating the orientation and relative position is related to the associated figure, and indication of the orientation and/or relative position has to be amended in different figures accordingly as the case may be.

Fig. 1 shows a schematic circuit diagram of a first example of a residual current breaker 1a. The residual current breaker 1a comprises a housing 2, first terminals T1 , T2 provided for being connected to a phase L1 .. L3, a first conductor 3 connecting said first terminals T1 , T2, second terminals T3, T4 provided for being connected to a neutral line N and a second conductor 4 connecting said second terminals T3, T4. Further on, the residual current breaker 1a comprises a first current sensor 5, which in this example comprises a first magnetic core 6 and first coil 7, which is wound around the first magnetic core 6.

In addition, the residual current breaker 1a comprises a switch S being arranged in the first conductor 3 and a trigger unit 8, the input of which is connected to the first current sensor 5 and the output of which is coupled to a control input of the switch S. In detail, the trigger unit 8 is connected to a latch 9, which is connected to the control input of the switch S in this example. Accordingly, the switch S stays open once the trigger unit 8 causes opening of the switch S and may be switched on again by the handle 10.

The residual current breaker 1a additionally comprises a DC current source 11 , a third conductor 12, which connects poles of the DC current source 11 , and a control unit 13. The residual current breaker 1a additionally comprises a second current sensor 14, which in this example comprises a second magnetic core 15 and a second coil 16, which is wound around the second magnetic core 15.

The third conductor 12, which connects poles of the DC current source 11 , runs in parallel with the first conductor 3 and the second conductor 4 at the first current sensor 5 and additionally at the second current sensor 14. The third conductor 12 is provided to carry DC compensation current lc, which is output by the DC current source 11 .

The first current sensor 5 and the second current sensor 14 are provided to measure a total current, which comprises a first current In ,.i_3 through the first conductor 3, a second current IN through the second conductor 4 and the DC compensation current lc through the third conductor 12. In detail, the total current is measured via a magnetic field caused by said total current.

The first magnetic core 6, which surrounds the first conductor 3, the second conductor 4 and the third conductor 12, is designed to guide the magnetic flux caused by said total current. The first current sensor 5, in this example its first coil 7, is designed to output a first current signal corresponding to said total current. The second magnetic core 15, which surrounds the first conductor 3, the second conductor 4 and the third conductor 12, is designed to guide the magnetic flux caused by said total current, too. The second current sensor 14, in this example its second coil 16, is designed to output a second current signal corresponding to said total current, too.

The trigger unit 8 causes the switch S being opened if (an AC part) of the total current exceeds an AC switching threshold based on the first current signal.

The input of the control unit 13 is connected to the second current sensor 14 and the output of the control unit 13 is connected to a control input of the DC current source 11 . The control unit 13 is designed to control the DC compensation current lc output by the DC current source 11 . In detail, the control unit 13 is designed to cause the DC compensation current lc to flow in opposite direction to a sum of a DC part of the first current ILI ..L3 and a DC part of the second current IN and to reduce a magnetic flux caused by a DC part of the total current by use of the second current signal.

In particular, the control unit 13 is designed to cause the DC compensation current lc to reduce magnetic fluxes through the first magnetic core 6 and the second magnetic core 15, in this example.

In other words, the residual current breaker 1a comprises a control loop with the DC current source 11 and the control unit 13, wherein the DC compensation current lc is the set value, wherein a DC part of the total current is the measured value and wherein in particular zero can be the target value.

The function of the residual current breaker 1a depicted in Fig. 1 is as follows:

In normal operation of the electric network downstream of the residual current breaker 1a, the first current ILI ..L3 equals the second current IN, and provided there is no DC compensation current lc, the total current ILI ..L3 + IN + lc is zero. Accordingly, magnetic fluxes through the first magnetic core 6 and second magnetic core 15 are zero as well. In turn, the current signals output by the first coil 7 and by the second coil 16 are zero, too. If there is fault current downstream of the residual current breaker 1a, this balance is disturbed and a fault current, which corresponds to the total current, occurs. Accordingly, there are magnetic fluxes through the first magnetic core 6 and the second magnetic core 15, and current signals are output by the first coil 7 and by the second coil 16 caused by the fault current. If the fault current or total current exceeds an AC switching threshold, the trigger unit 8 actuates the latch 9 which in turn opens the switch S and disconnects the electric network downstream of the residual current breaker 1 a from the grid as is known per se.

It can happen, that the fault current or total current does not only have an AC part but also a DC part. For example, this may happen when DC loads like for example electric cars have an isolation fault. If this DC part gets too high, the first magnetic core 6 and second magnetic core 15 can saturate what means that the current signals output by the first coil 7 and by the second coil 16 do not correspond any longer to the real fault current or total current. In other words, the residual current breaker 1a can get “blind”. Accordingly, the switch S is not opened reliably when the total current exceeds an AC switching threshold what can lead to dangerous and even to lethal situations.

To avoid such a dangerous situation, the control unit 13 causes the DC current source 11 outputting the DC compensation current lc, which in best case corresponds to a DC part of the sum of the first current ILI ..L3 and the second current IN. Accordingly, there is no effective DC part of the total current any longer. Hence, there is no risk for saturation of the first magnetic core 6 and second magnetic core 15 any longer, and the switch S is reliably opened when the total current exceeds an AC switching threshold.

It should be noted that the DC compensation current Ic does not need to correspond to a DC part of the sum of the first current ILI ..L3 and the second current IN, but a weakened effect is also obtained if the DC compensation current lc deviates from the DC part of the sum of the first current ILI ..L3 and the second current IN.

Fig. 2 shows a schematic circuit diagram of another example of a residual current breaker 1 b, which is very similar to the residual current breaker 1 a of Fig. 1 . In contrast, the second coil 16 of the second current sensor 14 is wound around the first magnetic core 6 here. In that, a separate second magnetic core 15 can be saved.

However, the function of the residual current breaker 1 b basically equals the function of the residual current breaker 1 a.

Fig. 3 shows a schematic circuit diagram of another example of a residual current breaker 1 c, which is similar to the residual current breaker 1 a of Fig. 1 and to the residual current breaker 1 b of Fig. 2. In contrast, the control unit 13 is connected to the first current sensor 5, in detail to its first coil 7. In that, a separate second current sensor 14 can be saved. Again, the function of the residual current breaker 1 c basically equals the function of the residual current breaker 1 a.

Fig. 4 shows a schematic circuit diagram of further example of a residual current breaker 1 d, which is similar to the residual current breaker 1 a of Fig. 1 . Instead of a first coil 7, the first current sensor 5 comprises a first magnetic field sensor 17, which is arranged in the first magnetic core 6, concretely in a gap of the first magnetic core 6, and which is designed to output the first current signal. Similarly, the second current sensor 14 comprises a second magnetic field sensor 18, which is arranged in the second magnetic core 15, concretely in a gap of the second magnetic core 15, and which is designed to output the second current signal. However, the function of the residual current breaker 1 d again basically equals the function of the residual current breaker 1a. For example, the first magnetic field sensor 17 and the second magnetic field sensor 18 can be embodied as Hall sensors, which are naturally capable of detecting DC signals. It should be noted that the second current sensor 14 alternatively may comprises a second magnetic field sensor 18, which is arranged in (a gap of) the first magnetic core 6. The function of the residual current breaker 1 d then basically equals the function of the residual current breaker 1 b of Fig. 2.

Fig. 5 shows a schematic circuit diagram of further example of a residual current breaker 1 e, which again is similar to the residual current breaker 1a of Fig. 1. In contrast, the input of the trigger unit 8 is (additionally) connected to the second current sensor 14. In this embodiment, the trigger unit 8 causes the switch S being opened if the total current exceeds a DC switching threshold. Hence, the residual current breaker 1e separates a downstream electric network from a grid even in case of DC faults. Fig. 6 shows a schematic circuit diagram of further example of a residual current breaker 1f, which has a similar function as the residual current breaker 1 e of Fig. 5. In contrast to the residual current breaker 1a of Fig. 1 , the residual current breaker 1f comprises a second trigger unit 19, the input of which is connected to the second current sensor 14 and the output of which is coupled to a control input of the switch S. In this embodiment, the second trigger unit 19 causes the switch S being opened if the total current exceeds a DC switching threshold. Hence, again the residual current breaker 1f separates a downstream electric network from a grid in case of DC faults.

Fig. 7 shows a schematic circuit diagram of another example of a residual current breaker 1 g, which again is similar to the residual current breaker 1a of Fig. 1. In contrast, the switch S does not only comprise a first switching contact arranged in the first conductor 3 but also a second switching contact in the second conductor 4. In turn, both a phase L1 ,.L3 and the neutral line N may be switched off in case of a fault.

Generally, it should be noted that in the Figs, just one first conductor 3 is depicted. However, a plurality of first terminals T1 , T2 can be provided for being connected to a plurality of phases L1 ,.L3 and for each phase L1 ,.L3 a first conductor 3 can provided, the current trough which contributes to the total current. In other words there may be a plurality of first conductors 3 being lead through the first magnetic core 6 and the second magnetic core 15. Accordingly, also the switch S may comprise a plurality of first switching contacts, each being arranged in one of the first conductors 3.

In Figs 1 to 7, a third conductor 12 is provided to carry the DC compensation current lc. However, this is not the only possibility. Fig. 8 shows a schematic circuit diagram of an exemplary residual current breaker 1 h, which is similar to the residual current breaker 1a of Fig. 1 , but where the DC current source 11 is connected to the first conductor 3 at two connecting points with the first current sensor 5 and the second current sensor 14 in-between. Accordingly, the first conductor 3 carries the first current ILI ..L3 and the DC compensation current lc at the first current sensor 5 and at the second current sensor 14 in this embodiment. However, the function of the residual current breaker 1 h again basically equals the function of the residual current breaker 1 a. Fig. 9 shows a schematic circuit diagram of an exemplary residual current breaker 1 i, which is similar to the residual current breaker 1a of Fig. 1 and similar to the residual current breaker 1h of Fig. 8, but where the DC current source 11 is connected to the second conductor 4 at two connecting points with the first current sensor 5 and the second current sensor 14 in-between. Accordingly, the second conductor 4 carries the second current IN and the DC compensation current lc at the first current sensor 5 and at the second current sensor 14 in this embodiment. However, the function of the residual current breaker 1 h basically equals the function of the residual current breaker 1a and the residual current breaker 1 h.

Fig. 10 shows an example how the residual current breakers 1a..1h can be used. Concretely, Fig. 10 shows an electric network 21 , which comprises a main residual current breaker 1 , branched electric lines connected to the main residual current breaker 1 and a plurality of downstream residual current breakers 22a..22c, each being connected to one of the branched electric lines. The main residual current breaker 1 is embodied like the residual current breaker 1a..1 i as outlined before. In particular at least one of the downstream residual current breakers 22a..22c can be embodied as a combined AC/DC residual current breaker. The downstream residual current breakers 22a..22c may also have main circuit breaker functionality, i.e. may open in case of excessive load currents.

Advantageously, the main residual current breaker 1 does not need to be an expensive combined AC/DC residual current breaker like this is the case in prior art applications, but the use of the proposed residual current breaker 1a..1 i provides reliable triggering of the switch S as well like this has been explained hereinbefore. This is even true in case that comparably small and non-dangerous DC fault currents in the branches sum up to a dangerous DC fault current in the main residual current breaker 1 . So, the electric network 21 with the residual current breaker 1a..1 i is cheaper and less complex compared to a prior art electric network. One further drawback of prior art networks is that the main residual current breaker 1 cuts off all downstream residual current breakers 22a..22c in case of a DC fault although, for example, not all downstream networks are prone to DC faults at all. This is not the case with the disclosed main residual current breaker 1 . It is noted that the invention is not limited to the embodiments disclosed hereinbefore, but combinations of the different variants are possible. For example, the features shown in Figs. 4 to 9 can be combined with all other embodiments, and so on.

It should also be noted that although the problem of saturating current sensors 5 and 14 has been explained in context with magnetic cores 6 and 15, the invention is not limited to these current sensors 5 and 14 but the invention solves this problem also when other types of current sensors are used.

In reality, the residual current breakers 1a..1h and the electric network 21 may have more or less parts than shown in the figures. Moreover, the description may comprise subject matter of further independent inventions.

It should also be noted that the term "comprising" does not exclude other elements and the use of articles "a" or "an" does not exclude a plurality. Also elements described in association with different embodiments may be combined. It should also be noted that reference signs in the claims should not be construed as limiting the scope of the claims.

LIST OF REFERENCE NUMERALS

1 , 1 a..1 i (main) residual current breaker

2 housing

3 first conductor

4 second conductor

5 first current sensor

6 first magnetic core

7 first coil

8 trigger unit

9 latch

10 handle

11 DC current source

12 third conductor

13 control unit

14 second current sensor

15 second magnetic core

16 second coil

17 first magnetic field sensor I first hall sensor

18 second magnetic field sensor I first hall sensor

19 second trigger unit

20 connecting wire

21 electric network

22a..22c downstream residual current breaker

In ,.L3 current through first conductor I phase

IN current through second conductor I neutral line

Ic DC compensation current

L1..L3 phase

N neutral line

S switch

T1 , T2 first terminal

T3, T4 second terminal