I would really appreciate some advice please, so that I can order the necessary parts and instruct my Electrician accordingly. I am installing a Ground Source Heat Pump which requires a supply using a 100ma RCD and 40 amp C Rated MCB. The instructions say this is to avoid nuisance tripping and the 100ma RCD is to provide protection against fire. This is part of a new build barn conversion, so the starting point is a BG metal twin 30ma RCD CU, which also allows for unprotected ways or RCBOs. The CU is already fitted and supplies the circuits to the conversion. There is not much room to split the incoming meter tails and I wondered whether we could use a spare fuseway for the 40a C Rated MCB then into a separate enclosure and through the 100ma RCD to the heat pump, or is there an easier way ? With many thanks.