Ground fault protection in TN/TT (grounded) electrical systems: RCM and MRCD
 
On the other hand, Modular Residual Current Devices or MRCDs have as their main function the interruption of the electrical supply in case of reaching the preset ground fault threshold, said values ​​typically being 30mA for protection of people or 300mA for protection of equipment (IEC60947- 2, annex M).
 
However, and in order to offer the added value of advanced information in the evolution of ground faults, Bender's MRCDs also have a pre-alarm threshold (warning) and another alarm threshold (disconnection).