What it is called, by market
One concept, four markets. Where a name means something else locally, the card says so rather than leaving you to find out on site.
United Kingdom
Same word, different thingring final circuit
also ring main, ring circuit, radial circuit
Ring MAIN is the common trade term and is technically wrong — a main is the supply into the building, not the final circuit off the board. Radial circuits also exist in British practice and are increasingly specified.
Australia
Close, not identicalfinal subcircuit
also power circuit, radial circuit
Australian practice is radial rather than ring, so the term describes the same position in the system with a different topology behind it.
United Statesyours
No local equivalentbranch circuit
also circuit, small appliance branch circuit, home run
There is no ring. Each branch circuit leaves the panel and terminates, and loop wiring of socket outlets is not a recognised arrangement.
Canada
No local equivalentbranch circuit
also circuit, split receptacle circuit
As the United States, with the split-receptacle kitchen arrangement a Canadian particularity that has no British counterpart.
The governing standard, by market
United Kingdom
BS 7671 Appendix 15
Ring and radial final circuit arrangements, conductor sizes and the conditions for each.
United States
NFPA 70 (NEC) Article 210
Branch circuits: ratings, required outlets, and the circuits a dwelling must have.
Calculators for this
Each works in either measurement system, and the terminology on the page follows whichever market you have selected.
Frequently asked questions
- Why does a British plug have a fuse in it and an American one not?
- Because the ring circuit protects the cable in the wall, not the flex on the appliance. A ring final circuit is typically protected at 32 A, since current can reach any socket along two paths and the cable is sized on that basis. But the flex on a table lamp is nowhere near able to carry 32 A, so something has to protect it — and that something is the fuse in the plug, sized to the appliance. An American branch circuit is protected at 15 A or 20 A, which the appliance cord can survive, so no fuse in the plug is needed. This is the clearest illustration that the plug is not a national quirk: it is a component of a circuit design, and it exists because the protection upstream is deliberately larger than any one appliance needs.
- What actually goes wrong if a ring is broken?
- It keeps working, which is exactly the danger. Break one leg of a ring — a loose terminal, a screw through a cable, a socket wired through instead of looped — and every outlet still has power, because current simply arrives the long way round. But the circuit is now two radial legs protected by a 32 A device, and a leg carrying its full share of the load on cable sized for a shared ring can overheat without ever tripping anything. Nothing on the surface indicates it. That is why a ring is tested by measuring end-to-end continuity of each conductor and cross-connecting them rather than by checking that the sockets work, and why a break is one of the commonest findings on an inspection of an installation that has been altered by non-electricians.
- Is a ring better than a radial?
- It is a trade, and British practice increasingly chooses radial for new work. A ring uses a smaller conductor for a given load because current shares two paths, which mattered a great deal when copper was scarce after the war and is the reason the arrangement exists at all. It also allows a large floor area on one circuit. Against that: a ring depends on remaining continuous, it is harder to test and far easier to compromise during alterations, and a fault anywhere on it affects a large part of the house. A radial circuit is simpler to verify, simpler to extend, and fails in a more contained way, at the cost of more cable or a larger conductor. Neither is a correction of the other; the ring is a design optimised for a constraint that has largely gone.