How ELCB works?

ELCB is popularly known as RCCB ( Residual Current operated Circuit Breaker). Its works by sensing the leakage current. Inside the breaker there is CBCT( core balance current transformer) which sense the abnormality.

Hello sabith

If you have two coils on top of each other (one for phase, one for neutral) both fields cancel each other completely. If there is somewhere a leak to earth, the currents in both coils are no longer the same, so the switch is triggered by the resulting electromagnetism.