I mostly do additions and alterations, infrequently new circuits, very rarely (partial) rewires. I've installed RFCs in new installs where voltage drop would have otherwise been an issue (e.g. upstairs sockets on large area 4-bed house), but otherwise install radials where I can.
The issue with RFCs, even correctly-installed ones, is you never know what you're going to find, which makes it harder to do a quote for a trivial job of adding another socket, because you never know (visually) if an existing socket it on the ring, or a spur. Yes, you can turn the circuit off, have a look behind, and check r1 rn r2, but that's a fair bit of faff when you're just popping round to do a quote. If it's a B20 or B16 supplying a radial circuit, then I smile because I just do a quick Zs check at the socket I'm going to extend from and - other than insulation resistance - the number of unknowns is massively reduced.
A typical case will be adding an outside socket on the back wall of the house, where there's an existing socket in the kitchen cupboard (or behind the washing machine). If it's on the ring - great! Add a DP isolator (or 13A SFCU), drill through the back wall, and away you go. If it's a spur? Sure, could add a 13A FCU to feed the existing socket, plus the new outside one... but what if the existing spur is a 2G socket that feeds a dishwasher and washing machine (or worse, tumble dryer)? The 13A FCU will end up working beyond its capacity, whereas the unfused spur supplying the two appliances on the existing 2G socket would have been fine.
So I propose a new Regulation:
433.1.205: Unfused spurs on a RFC should be clearly marked as such, either using a permanent label, or a small indication in the bottom right hand corner of the plate that can be seen with a UV light or similar
I sleep soundly at night adding a 3A SFCU feeding an outside LED light (or a doorbell) to an unfused spur (with an existing 1G or 2G socket on it)... doesn't match the guidance in Appendix 15 (Informative), but does comply with 433.1.204 as the few extra mA of current are not going to make a jot of difference to the safety of the unfused spur.
