Post WW2 for newly built small flats, ring mains were designed to save on copper (as it was in shortage). The intention was to allow for 3-bar electric fires t

Post WW2 for newly built small flats, ring mains were designed to save on copper (as it was in shortage). The intention was to allow for 3-bar electric fires to be operated as 13A loads, and be moveable between rooms. Rings are more complex to test, and have nasty failure modes. I'd argue that they should only be used in said small flats, and that 20A bus/radial runs should be used in larger builds. i.e. any modern house, rather than a flat. Said run the supplying all of the sockets in any given room, it does though require a larger "consumer unit". The rings have a 30A (or now 32A) at the "consumer unit" (distribution fuse box) with two cables running in a loop around all sockets in the circuit. The cables have traditionally been 2.5mm, and open clipped, so rated at around 27A (based upon preventing overheating). Hence when operating properly, the wiring in the circuit can carry 54A, the circuit is fused at 30A (or 32A) to protect the cable, and an individual load is limited to 13A (being the highest cartridge fuse commonly available). Have a look here: https://www.diydoctor.org.uk/projects/cablesizes.htm https://www.diydoctor.org.uk/projects/cablesizes.htm