Hi Bill & Electure:
Your two posts are somewhat related, so I'll try to answer them together.
Yes, we do have ring circuits and fusing at point of use. The ring arrangement was introduced in the late 1940s. Prior to that we had several different types of plug in use, rated at 2, 5 and 15 amps, all with round pins.
The ring arrangement saw the introduction of a new type of plug which was intended to be a universal connector for portable appliances. A ring circuit is wired from a 30A fuse or breaker at the panel to each socket in turn and back to the panel to complete the ring. All three conductors (live, neutral, earth) are wired in a ring.
30 amps at 240V is a lot of power, so the house fuse is there just to protect the ring wiring. The plug has three rectangular pins and is rated at 13A max. (chosen to allow for a load of up to 3kW). Every 13-amp plug (known officially by Briish Standards as a BS1363 plug) is fitted with a small cartridge fuse, which is available in several different ratings up to the 13A maximum.
Advantages of the ring:
A 30A ring can provide up to 7200W and can serve a large area (up to 1000 sq. ft. for each ring is the accepted limit). Each portable appliance has its own fuse in the plug. Smaller, easier-to-work cable can be used than would otherwise be needed for a 30A branch.
Disadvantages:
Overcurrent protection for the cable relies on the integrity of the ring; a broken live or neutral will still leave all outlets energized, but a dangerous overload could occur. Mr. Joe Public often has no idea what size fuse should be in each plug and runs everything with a 13A fuse "Because it's a 13-amp plug." Adding extra outlets entails more work to maintain the ring. DIY extensions often result in a broken ring or a dangerous spur (spurs are O.K. under certain conditions).
These are some of the main pros and cons put forward frequently. Personally, I'm not that keen on rings and prefer other arrangements.
Over to you...
