Residual currents caused by the failure of insulation can constitute a significant risk to safety in electrical systems. Using an appropriate protective concept it is possible to detect residual currents, eliminate insulation faults in good time and therefore ensure the availability of the system.
RCM stands for Residual Current Monitoring and means the monitoring of residual currents in electrical systems. This current is calculated as the sum of the currents of all conductors, apart from the protective earth (PE), which feed into the system. Residual currents are typically the result of insulation faults, leakage currents or EMC filter leakage currents for example.
through the use of residual current measuring devices
through the information additionally gained from an RCM measuring device
RCM devices record the long-term development and report the exceeding of critical value
RCM measuring is based on the differential current principle. This requires guiding all phases (without PE) through a residual current transformer at the measuring point - the outlet to be protected. If there is no failure in the system, the sum of all currents will be nil. If, however, a residual current is flowing to ground, the current difference causes an evaluation by the electronics in the RCM measuring device.
RCM measuring instruments are mainly used in systems where a high level of availability is required, such as:
• Data processing centres, production and telecommunications facilities, hospitals, etc.
• TN-S systems with strict EMC requirements
• Equipment at risk of fire
• Equipment in cleanroom conditions
• Research facilities, laboratory technology areas
• Insulation faults of lines and electrical operating resources
• Residual currents from electrical loads
• Defective PP power capacitors for the PFC
• Defective components in switched mode power supplies e.g. in computers
• Correctness of TNS systems (Terra Neutral Separate)
• Disclosure of impermissible PEN connections
• Avoidance of neutral conductor reverse currents to grounded equipment
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