OP
sles
Of course calculation is a cop out i know . However I just remember that when i was in training i asked the question can i change for an mcb and test and they said no because your not actually testing the circuit as it will be in operation, i.e the mcb may function perfectly but the rcbo not. You're probably right but just a thought .
Cheers
Nothing in the testing procedure tests that an MCB will actually trip as described in its characteristics curve so you have no means of determining an MCB function or the overload section of an RCBO (RCD section trip times still apply with the RCBO of course!).
Sectioning and isolating elements of a circuit is normal - think what you do if there is a dimmer switch in line or example
Steve