lol i have a £2500 robin loop/rcd I/R testers and have have checked various thing and taking a sub main of the main breaker still does not give you a cleaner supply than if you have a spare way on your non rcd side of your board, if you have a 17th edition spilt load board then you can put it on the non rcd side but the only true way of getting a cleaner circiut is to get 3 100amp blocks at meter and take fresh tails25mm and 16mm earth to a 40amp 1 way {30ma rcd board} and feed a radial circuit 16amp type A with micc cable but that would not be cheap. So i would say that as long as you have your power coming off a breaker with no elements or coils on it you would be fine. This all my views and im sure some people will differ