RCMs (residual current monitors) when used in combination with separate residual current transformers allow the monitoring of insulation between active conductors and the earth conductor. In contrast to modular residual current devices (MRCDs) or residual current circuit-breakers (RCCBs), they are used where the system either cannot or should not be switched off. In this way, these devices alone are used to monitor or report residual currents and are therefore suitable for preventative maintenance. They are not suitable for implementing protective measure "Automatic switch-off of power supply" as per DIN VDE 0100-410. Monitors with residual current characteristic A detect sinusoidal AC currents as well as pulsating DC residual currents. Series DRCM residual current monitors Devices in the standard design are intended for monitoring circuits with a rated voltage of 230 V or 400 V and a rated frequency of 50 Hz or 60 Hz.