I have an installation where for various reasons it's going to be impractical to fully comply with regs.
I am planning on adding to an installation where the existing CU is in the middle of the house, full and very limited room around it.
Moving the CU and the supply head would be prohibitively expensive so I am looking at teh next best option. Customer is adding the EV charger, some outside lights and also power to an extension that I am not involved with.
I think the best way forward for the EV charger and outside lights is to add a small DB on it's side just under the existing CU or ideally replace the existing CU and gain a couple of extra slots in the space available. Then run a sub main out to a separate DB for the outside lights and EV charger.
But for this question I want to focus on RCD protection. To get cables to the new DB located under the stairs they will have to run through the ceiling. The beams are 6 inches deep and I plan to use twin and earth for the submain as the route is quite convoluted and awkward to run SWA all the way.
From my understanding :-
Concealed cables should be protected by a 30mA RCD
The outside lights and the EV charger should also have individual RCD's protecting them in the sub DB.
This means I will have no selectivity between the 30mA rcd on the sub main and RCD's on the individual circuits.
So do I use a 100mA type S RCD on the sub main or accept there will be a lack of selectivity.
I am leaning towards using a 100mA type S on the sub main as the customer won't be happy if the ev charger fails due to lighting issue, what are your thoughts?
