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The AC/DC sensitive MRCDB300 device series is used as additional protection (protection against indirect contact) in earthed systems (TN and TT systems) in which AC or DC fault currents may occur.

Part of these systems are particularly loads containing six-pulse rectifiers or one-way rectifiers with smoothing, such as converters, battery chargers, construction site equipment with frequency-controlled drives. When the response value IΔn2 (alarm) is reached, the output relays K1 and K2 switch.

By using an MRCDB300 module and a switching element with isolating properties, the device combination fulfils the requirements of IEC 60947-2 Annex M for an MRCD protective device.

The application is specifically intended for protection goals such as protection of persons, fire protection and plant protection. The switching element must not exceed a switch-off time of 20 ms.

The residual current monitoring modules each consist of the MRCDB300 evaluation electronics and a CTBC20(P)…210(P) series measuring current transformer core. To assemble a complete module, both the electronics and a measuring current transformer core are required; if ordered separately, these two components must then be plugged together and calibrated during commissioning.

The CTBC20P…210P series measuring current transformers feature an integrated magnetic shield and are suitable for applications with high load currents or inrush currents.


  • Structure of a protective device in accordance with IEC 60947-2 Annex M in combination with a circuit breaker providing isolating properties
  • Monitoring of the connected circuit breaker by means of contact feedback
  • RS-485 interface with Modbus RTU (reading out measured values/setting parameters)
  • Integrated switching outputs with two changeover contacts K1 and K2 (galvanically isolated)
  • Fulfils the protection goals protection of persons, fire protection and plant protection (depending on the variant)
  • Frequency range DC…100 kHz
  • Combined test and reset button
  • Multicolour LED indicating operation, exceeded response value, disturbances and status messages
  • AC/DC sensitive type B measured value acquisition acc. to IEC 60755
  • AC/DC sensitive type B+ measured value acquisition acc. to VDE 0664-400
  • Exchangeable electronic enclosure without mechanical separation of the primary conductors
  • Extension/retrofitting or modification of functionalities in case of changed monitoring requirements
  • Insensitive to load currents due to full magnetic shield (CTBC20P…210P only)
  • Connection monitoring of the measuring current transformer with cyclical test current
  • Use of all MRCDB300 for all CTBC… measuring current transformer sizes
  • Supply voltage DC 24 V


  • for MRCD applications

LINETRAXX® MRCDB300 series Variante/i

Composition of an MRCD modue:
Electronic module + Measuring current transformers = MRCD modul

Electronic module

TypeSupply voltage USVariantArt. No.
MRCDB301DC 24 V (19.2…28,8 V)Protection of personsB74043120
MRCDB302DC 24 V (19.2…28,8 V)Fire protectionB74043121
MRCDB303DC 24 V (19.2…28,8 V)Protection of persons, fire protection and plant protection (freely configurable)B74043122
MRCDB305DC 24 V (19,2…28,8 V)Protection of persons for applications with pulsed,
very high peak load currents (> 1 kA for < 1 s), e.g. welding applications

Required terminals are included in the scope of delivery.

Measuring current transformers

TypeInternal diameterArt. No.
CTBC2020 mmB98120001
CTBC20P20 mmB98120002
CTBC3535 mmB98120003
CTBC35P35 mmB98120004
CTBC6060 mmB98120005
CTBC60P60 mmB98120006
CTBC120120 mmB98120007
CTBC120P120 mmB98120020
CTBC210210 mmB98120008
CTBC210P210 mmB98120021

P = full magnetic shield

Accessori opzionali per LINETRAXX® MRCDB300 series


DescriptionArt. No.
Interface converter USB to RS-485B95012045
Terminal block for MRCD module*B74043124
Snap-on mounting for CTBC20 and CTBC20P*B91080111
Snap-on mounting for CTBC35 and CTBC35P*B91080112

* Included in scope of delivery

Voltage supply

Typmax. connected current transformersArt. No.
STEP-PS/1 AC/24 DC/1.7514B94053111
STEP-PS/1 AC/24 DC/4.234B94053112

Download per LINETRAXX® MRCDB300 series

Certificatos TÜV NORD - AGH150x, CTACx, CTBCx, EDS44x, CTUB10x, MRCDB30x and RCMB30x 417.2 KB EN2023/01/12 14:43:5312.01.2023 14:43:53
Certificatos TÜV NORD - AGH150x, CTACx, CTBCx, EDS44x, CTUB10x, MRCDB30x und RCMB30x 437.3 KB DE2023/01/12 14:43:4612.01.2023 14:43:46
Dichiarazioni di conformità CE MRCDB30x 87.4 KB 2022/08/12 06:17:2512.08.2022 06:17:25
Dichiarazioni di conformità CE CTxx 89.3 KB 2022/11/04 06:57:2904.11.2022 06:57:29
Data sheet MRCDB300-Serie 892.3 KB DE2021/08/25 07:14:4525.08.2021 07:14:45D00343
Data sheet MRCDB300 series 889.6 KB EN2021/08/25 07:15:0825.08.2021 07:15:08D00343
Quickstarts MRCDB300-Serie 1.3 MB DE2022/06/09 10:52:1409.06.2022 10:52:14D00343
Quickstarts MRCDB300 series 1.3 MB EN2022/06/09 10:52:1409.06.2022 10:52:14D00343
Manuali di istruzioni MRCDB300-Serie 2.2 MB DE2021/08/27 08:28:2527.08.2021 08:28:25D00343
Manuali di istruzioni MRCDB300 series 2.2 MB EN2021/08/27 08:29:0627.08.2021 08:29:06D00343
Data sheet MRCDB300 série 893.6 KB FR2021/08/25 07:15:4225.08.2021 07:15:42D00343
Flyer Modulares Fehlerstromgerät MRCD 96.6 KB DE2021/05/18 08:01:5218.05.2021 08:01:52
Flyer Modular Residual Current Device (MRCD) 96.3 KB EN2021/05/18 07:41:3318.05.2021 07:41:33
Flyer Dispositivo de Corriente Residual Modular MRCD 98.2 KB ES2021/05/18 08:03:1118.05.2021 08:03:11
Flyer Dispositivo differenziale separato a toroide esterno MRCD 115.1 KB IT2021/05/18 08:05:0218.05.2021 08:05:02
Data sheet MRCDB300 serie 891.7 KB ES2022/06/09 10:55:5209.06.2022 10:55:52D00343
Manuali di istruzioni CTBC-Serie 1.0 MB DE2021/11/24 10:20:4824.11.2021 10:20:48D00336
Manuali di istruzioni CTBC series 1.0 MB EN2021/11/24 10:20:5924.11.2021 10:20:59D00336