safety of man while working with a machine

They are two terms for the same thing.

Well, technically one is a subset of the other, but in practicality they are the same. ELCB stands for Earth Leakage Circuit Breaker, which generically means it is checking to see how much current is flowing to earth (ground for us Americans). RCCB stands for Residual Current CB, meaning that this type of ELCB is using the Residual Current method of calculating the amount of flow to earth. Measure all three currents out, the current returning on opposing phases should be the same. Any residual value means some of it is going somewhere else, and that must be earth.

The other way to do it is called a Zero Sequence (ZS) method. That requires a Core Balanced CT (Current Transformer) and a different type of relay with a circuit that looks at the voltae created in the CT if the amount of curent flowing through it does not balance out between all 3 phases and Neutral (if applicable). The ZS method is better for some types of systems, i.e. those with resistance earthing, but requires more hardware than RC and is more expensive, thus making it impractical for all but the largest systems, i.e. the entire plant, not just one tool or machine..