Interesting Spin. Ok I presume the scenario is that a bathroom has had electrical work carried out in it and the following items for instance has been fitted as an example. (All items within specified zones) 1 - Towel warmer 2 - Underfloor heating Right it is decided that the above are to be taken off of a non RCD protected Ring Final as two spurs from said. Regulations dictate that the spurs must be RCD protected (or maybe the whole Ring Final) thus the fitting of FCU/RCD's are indicated. So the FCU's are fitted outside of the bathroom (but possibly could be placed inside subject to zones) So the items are RCD protected as per regulations - however from what I can gather the actual Ring Final itself has to be RCD protected which would obviously be at DB position and would negate the use of RCD/FCU's and allow the use of an FCU only. So presumably the argument is is that the whole Ring Final proper has to be RCD protected. and the use of RCD/FCU's is not allowed Quantification of the above - Bit difficult actually. The RCD/FCU spurs into the bathroom provides the necessary protection as does the RCD protected Ring Final without the RCD spurs. I can only look at things from a simplistic angle, but can really see no differentiation between the two methods - the end result is the same - all the named circuits in the bathroom are RCD protected. .but there must be more to this. Must go, all good stuff and will watch with interest.