Answer / m.s.srinivasan

Functioning of the RCCB as well as ELCB are the same.
A CT is used to measuer the difference of current in the
circuit being protected. For that all the 3 cores + neutral
of the circuit is passed thro' the CT. For a normal healthy
circuit, difference of the net current will be Zero. Hence
the CT will not sence any current. When the current passing
thro the CT finds a path thro' the some other way ( by
earth ) , an unbalance is created and the CT sences the
unbalance and actuate a trigger to stop the power flow.
The unbalance current over which the RCCB to operate is
given for individual device. Normaly this would be
30ma,100ma,300ma and the selection of the devices is based
on the application.

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