On Sat, 10 Apr 2021 01:04:28 +0100, John Rumm wrote:

On 09/04/2021 19:07, Clive Page wrote:
I just watched another of Tim Hunkin's excellent videos - this one is
on connectors:

https://www.youtube.com/watch?v=q43tZ6DjuIE

One of the connectors he deals with is the UK 13A power plug.Â* He
claims that it was introduced in about 1947 because of the copper
shortage.
The reasoning is that there was a post-war housing boom - I expect that
a lot of existing houses also needed re-wiring - but that the
conventional way of doing this by running a cable from the fuse-box to
each separate mains socket was deemed wasteful of copper.Â* So someone
invented the ring-main which generally used less cable.Â* The problem
was that the ring-main fuses had to be larger and so the system wasn't
as safe.Â* The solution was to put a fuse in each plug-top and this made
them much larger.Â* Does that sound a reasonable explanation?

Apart from the fuse making it larger part - Then that is the thrust of
it. A ring can serve lots of sockets with less cable and is easier to
wire if you need a high power delivery. It could also be cobbled
together from two existing 15A radials, and be far more versatile than
the sum of the parts. The modern implementation of the ring turning out
to be very well suited to modern applications (i.e. loads of sockets and
load of small loads)

In fact I can just recall the old 15 amp 3-pin plugs which preceded
them and I don't think they were all that much smaller even though they
were fuse-less.

Indeed - if anything they are larger.

In North America they don't seem to worry much about safety given their
lower mains voltage,

They don't but ought to (the number of electrocutions there per year are
staggering compared to ours!)

but what about mainland Europe - do they use ring mains with their
fuse-less plugs or does each socket have a separate run back to the
fuse-box?Â* I have never thought to enquire.

Most places use lots of radials serving just a few sockets, with the MCB
sized to offer both fault and overload protection to all of the circuit,
right up to the appliance.

(contra you our design where the MCB[1] offers fault and overload
protection for the ring circuit as far as the sockets, but the plug fuse
extends fault protection up to the inlet of the appliance).

[1] in conjunction with some design rules.

When I was young we had DC mains and the cooker control box had fused
15amp and 5 amp round pin sockets. The switches were the two pole rotary
type. All my experiments were done, using an ex WD rotary transformer used
in reverse, to get ~28volts DC.