差动电流互感器（剩余电流监控，RCM）

Difference current transformer (Residual current monitoring, RCM)

This type is specialised in the detection of residual currents in 3 / 4-wire AC networks.
Its special features are:
Highly sensitive current sensor for the detection of even the smallest residual currents, fixed switching hysteresis of 5%, high safety thanks to integrated overvoltage protection and coverage of a wide frequency range.