If this is a MCB whitout any electonics then yes or otherwise disconnect first any electronic equipment. Lights, relays, breakers, motors, transformers, etc. can all be tested if there insolation is good and depending on the use it can compulsery. Electronics do not like the high test voltage or its internal protection shorts making you look for a problem that is not there.
you mean first we de-terminate the cable from the main isolator of the distribution board then we can give supply to the isolator terminals without removing the outgoing wires to the sockets, lights, A.C's , water heaters and bla bla ...
