RCD and MCB ???? what they detect

could anybody explain exactly what the RCD can detect, and how it works, what it monitors, and what can cause it it trip e.g different situations what can make it trip,

and the same for an MCB???

whats the difference between them i can never get my head round what the differences are between them

thanks

MCB's are the modern equivalent of fuses.

They protect against overcurrent and short circuit, using thermal & magnetic elements in their design.

RCD's monitor the line & neutral currents. If there is an imbalance greater than the rating of the device, ie fault current lost, it will trip.

so does the rcd monitor the live and neutral together and if there is a leakage current to earth it will trip the RCD is that right?? I thought this would be called a short circuit and it would trip the mcb and not the rcd?

what the main differences between the mcb and rcd what can they both do and not do?

you might say that an RCD is very sensitive. Should an imbalance between line and neutral be detected, of lets say 30mA then it will trip, presumption being that this "current" is leaking either through a connection between live conductors and an earthing conductor or from a live conductor, via a human, to earth. It should do this, de[pending on application within 40ms and 300ms.

An MCB will detect an overcurrent, caused by overload, or short circuit between line and neutral or line and earth, but not so quickly.

ie, if you did not have an RCD and you made a good connection with earth from contact with a live connductor then the current would not be reduced in time or to below 50v to protect you