Earth Fault, Leakage & Circuit Breaker

Earth leakage equipment works by evaluating the vector sum of all currents passing through it. If this sum is higher than its trip setting, it trips.

Slam dunk.

There are now devices called "ELMCB"s. These are primarily RCD+MCB combinations, with the ability to sense overload and short-circuit also in addition to earth leakage, maybe capable of interrupting 6 or 10kA.

The right name for this device is RCBO - Residual Current Breaker with Overcurrent protection.

where did you encounter an earth leakage current of 30A? or did you mean 30mA?

. . . so when you use an RCBO . . . any earth leakage current higher than the set value causes the device to trip and disconnect the circuit . . . any overload current causes the O/L protection to take over and isolate the circuit . . . any very high current caused by short circuit (or "earth fault") causes the device to trip and disconnect the circuit . . .

the device to be used is selected by the specifier to ensure that the interrupting capacity of the device (6kA or 10kA are common in domestic use) selected is more than or equal to the possible "very high current" in the circuit even when there is a direct short circuit (or earth fault).

i have not encountered anywhere but i have seen a relay with a setting from 0.03A to 30A.

but when u say an earth fault(phase to ground), normal MCB or MCCBs doesnot trip. i have seen in the catalogues of major brands where they clearly mention whether ground fault protection is provided or not. for eg. in schneider electric, MCCB with TM trip unit doesn't have ground fault protection, while MCCB with Micrologic 6 does. and a normal MCB doesnt provide ground fault protection.

Micrologic 6 trip unit is a costly trip unit and is usually not used in SMDB or SDB.

can u please clear my query?

In MCCB with micrologic what is the method used to detect EF?. For other MCCBs too if you connect a core balance transformer or EFR it will trip. Even MCB can be fitted with tripping coil.

there is only earth leakage protection & not an earth fault protection.

As I understand your above mentioned doubt, so be sure that ELCBs are only for earth leakage protection and MCBs are for short circuit & Overload protection,so the earth fault is also to be considered as Short circuit, therefore If you need to protect a circuit from Earth Leakage + Short circuit then go with the combination of MCB+ELCB.

sir can u see my comment no. 7 and help me out?

The arrangement in sub DBs or CUs is ok but did you check main switchboards(MSB) where in some they use ELR with core balance transformer while in others they use EFR depending on Amp rating of incoming CB?. Upto what Amp rating of load (or incomer) ELR is used and why?.