In article , DeeBee
writes

Then yesterday, I had finished the tiled slash back etc and fitted the new
45A isolator, one with a single 13A socket in. So wired the oven and hob via
the single cooker outlet plate as mentioned above to the new isolator, then
put in a new run of 6mm back to the CU. The old cable was too short. When I
turned the CU back on again there was a load deep electrical "pop" from the
CU and the cooker 32A MCB and the split load RCD had tripped.


Check you haven't trapped the live conductor against the backbox in the
isolator (or anywhere else it runs). I recently had a ring main socket
where one of the knockouts in the rear of the backbox was slightly bent,
the sharp edge cut through the insulation of the live cable when I
fitted the socket plate and made a big bang when the power was turned
back on.
--
Tim Mitchell