MRCD ('Modular Residual Current Devices') consist of a combination of residual current transformer with evaluation unit and a separate, external shutdown device, e.g. a circuit breaker. In this combination, they enable the implementation of the measure 'protection by automatic shutdown of the power supply' in accordance with DIN VDE 0100-410 or IEC 60364-4-41. They are particularly suitable for use when RCCBs or CBRs cannot be used due to high load currents or mains voltages. The MRCD records the residual current and evaluates it in terms of its level and duration. If the limit values of the fault response current and the response time are exceeded, it controls a separate shutdown device, which in turn disconnects the part of the system to be protected from the power supply. Modular residual current circuit breakers of the DMRCD series are characterized by a large number of usable total current transformers - and thus also conductor cross-sections and rated currents. The bar display shows the current residual current. The alarm is signaled when a defined response threshold is reached. The level of the current residual current and the exceedance of the response threshold can be read on a 10-fold LED display on the front of the device. A faulty connection to the external residual current transformer is immediately indicated by a flashing code of the alarm LED and activation of the signal contacts. The adjustable response delay in the range of 0.1 s to 1 s (in steps of 100 ms) makes it possible to avoid a response to short-term residual current pulses, e.g. as a result of lightning strikes and switching overvoltages. This also makes it possible to achieve selectivity of devices connected in series, which makes fault localization easier. Two independent, potential-free changeover contacts offer the possibility of forwarding the alarm to optional alarm panels, indicator lights, acoustic alarm devices, touch panels, PLCs, etc. Modular protective devices with residual current characteristic A detect sinusoidal alternating and pulsating direct residual currents. These devices are suitable for monitoring circuits with frequencies from 50 Hz to 60 Hz. They differ in their setting ranges for the fault response current: the DMRCD 1 A allows the values 0.03 A, 0.1 A, 0.3 A, 1 A, 3 A to be set, the DMRCD 2 A allows the values 0.03 A, 0.1 A, 0.3 A, 1 A, 10 A to be set. Features: - suitable for detecting fault currents of type A, - monitored frequency range 50 Hz - 60 Hz, - fault response current adjustable in five levels, - selectivity adjustable in ten levels, - wide range of different residual current transformers available, - rated voltage of the monitored circuit up to 690 V, - with alarm relay, - adjustable pre-alarm threshold from 10% to 90% of the alarm response threshold,- the set value for the pre-alarm threshold is displayed as a continuously lit LED on the bar display, - potential-free changeover contacts for pre-alarm and main alarm, - compact, robust plastic housing, - easy to install, - in accordance with EN 60947-2 Appendix M, VDE 0100-410, IEC 670364-4-41, VDE 0100-530, EN 60664, Mounting type: - quick fastening on mounting rail, - installation position as desired, Areas of application: - The monitoring device is suitable for use in power supplies of commercial buildings and industrial plants with TN-S, TN-CS networks and IT networks, e.g. B. in server rooms of data centers, in laboratories, in the automotive industry and in connection with air conditioning systems, printing machines and packaging machines., - The device is not suitable for use in TN-C networks and direct current networks, nor for monitoring systems in which electronic equipment can cause smooth direct fault currents or fault currents with frequencies other than the rated frequency of the RCCB., Notes: The detection of