ELCB is the old name and often refers to voltage operated devices that are no longer available and it is advised you replace them if you find one.
RCCB or RCD is the new name that specifies current operated (hence the new name to distinguish from voltage operated).
The new RCCB is best because it will detect any earth fault. The voltage type only detects earth faults that flow back through the main earth wire so this is why they stopped being used.
The easy way to tell an old voltage operated trip is to look for the main earth wire connected through it.
RCCB will only have the line and neutral connections.
ELCB is working based on Earth leakage current. But RCCB is not having sensing or connectivity of Earth, because fundamentally Phase current is equal to the neutral current in single phase. That’s why RCCB can trip when the both currents are different and it withstand up to both the currents are same. Both the neutral and phase currents are different that means current is flowing through the Earth.
Finally both are working for same, but the thing is connectivity is difference.
RCD does not necessarily require an earth connection itself (it monitors only the live and neutral).In addition it detects current flows to earth even in equipment without an earth of its own.
This means that an RCD will continue to give shock protection in equipment that has a faulty earth. It is these properties that have made the RCD more popular than its rivals. For example, earth-leakage circuit breakers (ELCBs) were widely used about ten years ago. These devices measured the voltage on the earth conductor; if this voltage was not zero this indicated a current leakage to earth. The problem is that ELCBs need a sound earth connection, as does the equipment it protects. As a result, the use of ELCBs is no longer recommended.
