He is trying to make the position that, if the whole circuit is supplied through a 13A fuse, then a 32A MCB isn't going to do anything, as the 13A fuse will always blow first.
The basis of fuse discrimination is that the higher rated protective device is nearest the supply. Its poor deisgn to do otherwise,
But that is nothing to do with your RCD problem.
Am I missing something here?
A retired electrician puts in a CU with RCD on an existing 13 amp circuit that is already RCD protected.
The mind boggles.
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