The main objective of any plant operator is to detect malfunctions in good time and to eliminate the cause of malfunctions in order to achieve a high level of reliability and operational safety, which directly translates into saving money. This is particularly true for
- electronic data processing centres, EDP equipment and installations
- office and administrative buildings
- hospitals, doctors´ surgeries, banks
- power supply and distribution
- safety systems in power stations
- TV and radio engineering
- communication systems
- traffic engineering
- drives in continuous production processes
- airports
- industrial plants
- domestic technique
and many other facilities.
RCMs (Residual Current Monitors) monitor residual currents in electrical installation, indicate the currently measured value , by means of an alarm, and provide a warning signal when the residual current exceeds a predetermined level. The devices can be used for signalling and/or switching. The RCMs comply with DIN EN 62020 (VDE 0663): 1997-07 „Elektrisches Installationsmaterial –Differenzstrom-Überwachungsgeräte für Hausinstallationen und ähnliche Verwendungen (RCMs).“ IEC 62020 1998-08 „Electrical accessories – Residual current monitors for household and similar uses (RCMs).“
Unlike RCMs, the intended use of
RCDs (Residual Current Protective Devices) is to provide protection in electrical installations in accordance with the series of standards DIN VDE 0100 and IEC 60364, e.g. in bathrooms. RCDs always cause power disconnection.
All conductors in the load circuit to be monitored (with the exception of protective earthing conductor) are routed through the measuring current transformer. In a fault-free system the sum of all currents is zero, so that no voltage is induced in the measuring current transformer. If a fault current (IF) flows via earth, the difference in current in the measuring current transformer generates a current flow which is detected by the RCM. This method of measurement applies to RCMs for pure alternating current and pulsating direct fault currents (Type A as per IEC 60755).
With RCM(A)s of Type B, special measuring current transformers and a special method of measurement are used for the detection of direct and alternating currents.
Series RCM: 
Type A residual current monitors for monitoring alternating currents (40 … 400 Hz) and pulsating direct currents.
Series RCMS: Type A multi-channel residual current monitoring system for monitoring alternating currents (40 … 400 Hz) and pulsating direct currents.
Series RCMA:
Type B residual current monitors for monitoring alternating currents, pulsating and smooth direct currents (DC 0 … 1000 Hz).
