OP
Deleted member 9648
I have a cu with a main switch/ faulty rcd, eg It doesn't trip under 5x 40ms and 1x 300ms.
As the board is an old one, without finding a replacement if ones possible, is it aloud that I put one in front of this rcd?
I don't see a problem myself, they don't want the whole new cu cost but would be happy with a new rcd before the board, leaving the rcd in the board that's not tripping with in max time.
What the above posts are implying is incorrect test procedure. Have you tested this RCD in isolation with no loads connected?It's rare in my experience for RCD's which do trip to fail to trip in the permitted time,older Bs 4293 RCD's are especially reliable in this respect. It's nearly always the case that an RCD is tested with loads connected which will give a higher trip time,particularly loads with a capacitor such as a fridge or fluorescent light. Test the RCD on its output terminals with all final circuits isolated.