Well a new Type C RCBO fitted to the main CU unit (feeding the garage CU) hoping this would sort the issue but it hasnt. Electric tripped today on start up of tbe Xps2/ndx2.
Electrician has also taken the RCD from the garage CU out altogether, as well as the RCD trip swotch in the main CU out altogether.
At a loss now, he’s coming back Friday morning to investigate and bringing a meter to finally test the circuit. This has dragged in far too long.
A Type C breaker is usually effective at eliminating ‘nuisance’ tripping from the high inrush current of the large Naim transformers. If they are still tripping that would tend to indicate a fault, the whole point of the breaker being to deploy when it detects one. So there could be a fault either in your XPS or in the wiring, possibly hidden within your walls. Hopefully your electrician can identify this and fix it.
(Multiple breakers connected in series also are more prone to tripping when you switch things on. Best avoided where possible, including where one consumer unit is fed from a spare slot on another. This is another reason to split your meter tails and run a dedicated CU independently of the main house CU.)