Answer / asif mansoori

All 3 devices are used for protection from Earth Faults.

Earth Leakage Circuit Breaker is used for putting the circuit off in case any residual current passes out of the circuit & the difference is more than the rating of leakage current, e.g. 300mA, the circuit breaker will go off or cause the main circuit breaker to trip. Usually ELCB is comprising of one main circuit breaker and leakage breaker.
Nowadays, MCB+RCCB acts as RCBO or ELCB. If you use RCCB alone, only protection from leakage current is achieved, if you use both MCB & RCCB, then you get protection from both overload, short circuit and leakage.

ELR is earth leakage relay which is available standalone relay with dry contacts for externally tripping the main circuit breaker.

ELS is also type of ELR, but this is sensor & rating of this is lesser than ELR. For smaller leakage currents, ELS is used.

ELCB-Earth Leakage Circuit Breaker
ELR- Earth Leakage Relay
ELS- Earth Leakage Sensor

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