The RCB works on the principle of current balance.
The Incoming conductors (Phase & neutral) are passed through the very
sensitive torroid transformers from the primary winding and secondary
electromagnetic relay, which operates the trip mechanism. Normally the
contracts are held closed by a spring and open when this is released. If
leakage occurs from either of phases or neutral side of circuit in this
condition currents are unbalanced by an amount of leakage current and if
this reached the rated tripping current of RCCB/ELCB then it trips and save
precious human life.
Test button is for testing the trip mechanism of
RCCB. The test should be made periodically to ensure satisfactory working of