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Earth leakage circuit breaker generally check that supply wire (L) and return wire (N) has equal current,
ie current from L has no connect to earth . (1-Phase device )
Overload and short circuit protective device are different parts, they can be inbuild to ELCB device.
3-phase working principle is similar,
check sum of vectors L1+L2+L3+N , if equals zero = no gleak to ground.
Kak111 has described an RCD, that is a Residual Current Detector. Its a modern thing. If you want it to trip on overloads you need an RCBO. An ELCB was an old fashioned set up with a breaker with a trip coil which needed 50V to trip it. This trip coil was wired between the earth return of an electrical installation and the true earth. When the earth leakage current of an installation (which flowed through the coil) got too high, the breaker tripped. Problem is that any faulty installation earths that shorted or are connected to a true earth also shunts the trip current away from the trip coil coil so stops the ELCB working.
Frank
What pushed to that question that i found in a panel MCB connected to the power source then the 4 poles of the MCB are connected to the ELCB which is connected to smal breakers for power distribution....
The question is if the ELCB can protect from short circuit and overload why some designs require to use both mcb and elcb at same time?! What is the role of the mcb then?
You have missed the point an ELCB or more likely a RCD only protects against earth faults NOT current overloads. To protect against both in one device you need a RCBO.
Frank
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