What I was getting at here
Just to add, a CU change is not always neccessary, there are other options to add RCD protection
.
The Regs don't apply retrospectively, and it is not always necessary to try to bring the whole installation up to date in one go, even though this would be my preferred option, and it would be better, safer and likely the cheapest option in the long run.
For instance if you wanted to say add a shower, obviously the upstairs lights (or bathroom etc.) and the shower would need either a seperate (2 way) small cu, with an RCD and MCBs, or better two RCBO's etc., the bonding etc. may or may not require updating (which earthing system ?) each situation is different.
I was just pointing out we
have to work within the regs and often within the customers budget, and it is not easy having to marry the two, there is always more than one way of achieving a solution to a given problem, not always the preferred or the the best way.
This is what makes this trade so interesting