There are so many differences between these two by feature and application, however, few of them are as below:
1- MCB(Miniature Circuit Breaker) is for basic protection device to limit the current and fault in a circuit whereas ELCB(Earth Leakage Circuit Breaker) is advanced one which responds only when the circuit leaks current to earth
2- As per principle, the MCB works on the measurement of the incoming current of the circuit and its rise while the ELCB works on current balancing principles, which means it measures the net of incoming current and outgoing current. Any difference in both indicates the residual current which leaking to earth.
3- Based on the application of use MCB can be a different type with its characteristics curve whereas ELCB is only instantaneous type only because for any earth fault it should act immediately
4- The trip ELCB indicates more alarming issue the circuit than the MCB. Hence unlike reset of MCB, before resetting and ELCB its recommended to check the circuit thoroughly.