63a 30ma 2 pole, 2-module RCD

RCDs (Residual Current Device) sometimes called RCCBs

RCDs available in 25a to 100a versions, 30ma to 100ma 2 pole versions.

RCDs monitor neutral and earth for an imbalance which would normally indicate a leakage to earth.  Once this exceeds a pre-determined amount the RCD will trip.  It is important to note that they are designed to operate within a percentage amount of the RCDs maximum sensitivity and not run right up to the maximum sensitivity shown on the RCD.