ELR is earth leakage relay, and main attraction is its high
current rating, and it can use with CT also(with suitable
ELCB are less current capacity ELRs and using ferromagnetic
substances with differential relay.
ELR or commonly known to be EL CB . all 3phsaes and netral
of the incommin supply passs throuh oone ring type ct so
that there will be no current in CT secondary if there is
healthy system but in case there is a ground fault at load
end the cT will record the unbalance current and the relay
will sence the fault.beacuse durring ground fault the fault
curent will pas througth ground to the sourcr insted of
throug the neural inside the ring CT.