Why the wide prong on a plug?

The UK did redesign its plug and socket )and wiring system) during the war and postwar years to the now current 3-pin, fused 13A type. At that time, of course, there were far fewer electrical appliances in use, and a massive post-war housebuilding programme.

The postwar system uses unlimited numbers of 13A sockets (outlets) for general use within a limited floor area, wired on a ring and protected by a 30A fuse or 32A circuit breaker. This saved copper and allowed more flexibility than having a small number of sockets per fuse. It was considered unsafe to allow appliance flexes to be connected to such a high rated circuit with no further protection, and the plug/ socket combination had to provide the fuse. It was decided to place the fuse in the plug, and to use a new plug configuration so that older unfused plugs could not be used.

Fixed space and water heaters must be supplied by individual circuits, and good practice now is to provide a separate circuit for the kitchen which now has a large number of high load appliances unforseen in

See

One thing I really liked about the UK system was the availability of plugs with integral switches, so that appliances without a built-in switch could still be turned off without pulling the plug.

And, IIRC, separate circuits for lighting and sockets.

Perce

However, I couldn't find any of those the last time I was there -- 8 years ago.

Forgot to mention that the plug-mounted fuses came in a range of current ratings: 2A, 5A, 7A, 10A and 13A, IIRC. I think the plugs normally came with a 13A fuse, but one was supposed to install a fuse appropriate to the appliance to which it was to be connected.

Perce