Plant safety and operating safety are becoming increasingly important alongside the protection of personnel. Shutdowns due to the unexpected tripping of protective devices cause high costs. It is possible to detect residual currents in the electrical installation before the protective device responds.

Residual current monitors (RCM) monitor residual current in electrical installations and issue a signal when the residual current exceeds a set value.

RCMs werden vorwiegend in Anlagen eingesetzt, bei denen im Fehlerfall eine Meldung, jedoch keine Abschaltung erfolgen soll. Anlagenbetreiber können so Störungen erkennen und die Ursachen beseitigen, bevor die Schutzeinrichtungen der Installation abschalten. Dadurch werden Anlagen- und Betriebssicherheit erhöht und zudem die Kosten gesenkt.

RCMs are used primarily in plants where a fault should result in a signal but not in disconnection. This enables plant operators to detect faults and eliminate their causes before the protective devices disconnect the installation, which increases plant and operating safety and cuts costs.

The summation current transformer detects all conductors required to conduct the current, i.e. including the neutral conductor where applicable. In a fault-free system, the magnetizing effects of the conductors through which current is flowing cancel each other out for the summation current transformer, i.e. the sum of all currents is zero. If a residual current is flowing due to an insulation fault, a residual magnetic field is left in the core of the transformer and produces a voltage. This voltage is evaluated using the electronics of the RCM. The switched contact can be used e.g. to operate an acoustic/optical signaling device, a higher-level control system or a circuit breaker.