Bob F wrote:
"Claude Hopper" wrote
It would have been better to have redesigned the plug completely instead
of just widening a prong and adding a prong. A completely different plug
would have been almost impossible to modify to fit the old styles and
less safety bypasses would have been done.
Except for the need for "upward compatibility". How would you like to move to a
new house, and have nothing plug in?

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
1942.

See
http://en.wikipedia.org/wiki/BS_1363

Owain