"DeeBee" wrote
| 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.

Have you connected the neutral to the wrong neutral bar i.e. if the cooker
is on the RCD side you must connect its neutral to the RCD'd neutral bar.

Owain