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The residual current monitoring modules of the RCMB300 series are intended for measuring AC and DC fault currents in earthed systems (TN and TT systems). The modules are able to measure residual currents up to IΔ = 20 A in a frequency range of DC…100 kHz.

Two separately adjustable response values allow a distinction to be made between prewarning and alarm. When the response value IΔn2 (alarm) is reached, the output relays K1 and K2 switch.

The modules feature an RS-485 interface with Modbus RTU which can be used to transfer measured values and alarm values. Setting parameters is also possible via this interface.

The residual current monitoring modules each consist of the RCMB301 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 measuring current transformer cores of the CTBC20P…210P series feature an integrated magnetic shield and are suitable for applications with high load currents or inrush currents.


  • Continuous residual current monitoring in compliance with DGUV Vorschrift 3 (German Social Accident Insurance Regulation 3)
  • Easy DIN rail or screw mounting
  • RS-485 interface with Modbus RTU (reading out measured values/setting parameters)
  • Integrated switching outputs with two changeover contacts K1 and K2 (galvanically isolated)
  • 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
  • The AC and DC components as well as the r.m.s. value of the residual current can be evaluated separately
  • 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 the RCMB301 for all CTBC… measuring current transformer sizes
  • Supply voltage DC 24 V


  • AC and DC fault currents in earthed systems (TN and TT systems).

LINETRAXX® RCMB300 series Variante/i

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

Evaluation electronics

TypeSupply voltage USVariantArt. No.
RCMB301DC 24 V (19.2…28.8 V)Modbus RTUB74043100

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® RCMB300 series


DescriptionArt. No.
Interface converter USB to RS-485B95012045
Terminal block for RCMB301 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

Typemax. connected current transformersArt. No.
STEP-PS/1 AC/24 DC/0.54B94053110
STEP-PS/1 AC/24 DC/1.7514B94053111
STEP-PS/1 AC/24 DC/4.234B94053112

Download per LINETRAXX® RCMB300 series

Dichiarazioni di conformità CE CTxx 89.3 KB 2022/11/04 06:57:2904.11.2022 06:57:29
Dichiarazioni di conformità CE RCMB30x 88.1 KB 2022/11/23 07:29:4223.11.2022 07:29:42
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
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
Dichiarazioni di conformità RCMB30x - UKCA 121.3 KB 2022/12/20 06:00:0220.12.2022 06:00:02
Data sheet RCMB300-Serie 707.5 KB DE2021/03/23 08:01:0123.03.2021 08:01:01D00372
Data sheet RCMB300-series 659.7 KB EN2021/03/15 12:33:5415.03.2021 12:33:54D00372
Quickstarts RCMB300-Serie 339.4 KB DE2019/06/13 08:31:1513.06.2019 08:31:15D00372
Quickstarts RCMB300-series 322.3 KB EN2019/06/13 08:31:1413.06.2019 08:31:14D00372
Manuali di istruzioni RCMB300 Serie 2.2 MB DE2022/05/25 06:56:4925.05.2022 06:56:49D00372
Manuali di istruzioni RCMB300-series 733.7 KB EN2019/06/13 08:30:5813.06.2019 08:30:58D00372
Data sheet RCMB300 série 706.3 KB FR2021/03/22 14:37:2622.03.2021 14:37:26D00372
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