Residual Current Monitor

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A differential current measuring device (Engl. Residual Current Monitor, RCM ) monitors the differential current in electrical systems. This current is calculated from the sum of the currents of all conductors apart from the protective conductor (PE) that lead into the system. Differential currents can occur, for example, as a result of insulation faults.

While RCDs ( residual current protective devices, e.g. residual current circuit breakers or a modular solution ) switch off the power supply when a certain residual current is exceeded, RCM only show the current value and, if necessary, report the exceedance of a critical value via signaling contacts. This message can also be used to switch off the power supply via external switching devices (contactors, relays). As a rule, an RCM is used to give the user a message that there are errors in the system before the switch-off threshold of an RCD is reached. This means that if the values ​​slowly deteriorate, for example due to aging insulation, measures can be taken before the system is switched off.