What was the reasoning behind the ring circuit?
I've seen various claims and counterclaims over the years. The most usual seems to be that wiring with a ring saved materials, many of which were in short supply in immediate post-WWII Britain (even certain basic everyday items were still rationed until the early 1950s).
Prior to the ring, the standard arrangement was BS546 (unfused, round-pin) plugs and sockets rated at 2, 5 and 15A. Each 15A socket was wired on its own radial circuit back to the panel (or more likely a multitude of small 2- and 3-way units), and protected with its own 15A fuse. There would generally be a 15A outlet next to the fireplace in main living rooms for an electric heater, although they weren't always provided in bedrooms.
The 5A outlets could, according to IEE Regs., be wired three per 15A radial circuit, and were fitted in more generous quantities around the house for lower-power appliances (including smaller heaters). In practice, there were often more than three 5A sockets per circuit as wiring was extended.
The 2A sockets were intended for bedside lamps and similar and were normally wired on the lighting circuits (5A outlets could also be found on lighting ccts.).
The 13A rating of BS1363 plugs appears to have been chosen to provide for up to 3kW. Why 30A on the ring?
In the late 1940s central heating was rare. Most homes had open coal fires supplemented by individual gas or electric room heaters. My best guess is that with something in the region of 7kW to play with, it allowed the ring to supply two such 3kW loads and still leave a little room for smaller loads.
The heavy load of the ubiquitous electric kettle was almost always on the 15A (or 13A) socket provided on the cooker panel, and thus on the separate 30A cooker circuit rather than the ring. In fact in many kitchens of that time, that was the
only socket!
Here are some more old threads about the ring:
Ring circuits UK style Ring circuits revisited Ring circuits again! I've never seen a U.K. 13A socket in use here. If they were ever allowed here it must have been many moons ago, but I've never heard of it.
Mike posted a scan from some old N.Z. regs a while back which clearly shows both BS1363 and BS546 (round-pin) British outlets:
1961 Electrical Regs
