Why did the UK change from round pin to square pin plugs?

yes.

Yeah and with a 3-way BC adapter Mrs. could watch TV while ironing in the evening!

But that was a 13 amp plug, designed to be used with an ordinary ring main, with a matching socket. Very common in council houses at one time. No idea why.

Gawd knows. The fittings look incredibly ugly compared to the best 13 amp.

Just foreigners with no taste. ;-)

And the adapters often had a switch as well !

I see BS1363 (square pin plugs) was introduced in 1947 for AC only (according to Wikipedia). Were there any DC supplies left by the? What plugs would they use?

The ring system has clear advantages on cost & safety, yet close to no-one outside the UK understands how it works or what its upsides are. I find that strange but there it is. Our plugs are bulky compared to most countries, and using radials they don't need the plug fuse, so ours don't suit radial systems particularly well. And ours are a hazard to feet.

Both types are common, the earth pin operated ones more so. The MK LN pin operated ones are out of patent now.

Round pin and BC adaptors were in a lot of cases infinitely stackable. And occasionally excessively stacked. BS1363 gauge adaptors are specifically designed to not be stackable as one of the safety features of the 1363 system.

DC mains was still quite common into the 60s. I don't know about plugs, I just assumed they used the usual round pin ones.

Wasn't Reading another late survivor for DC?

Several locations had DC supplies maintained for lifting bridges, dockyard cranes and similar large motors. They often didn't appear in the main records because it wasn't a public supply, but there were a variety of odd deals between generators and consumers (often dockyards) to avoid the cost of remotoring or installing rectifiers.

I am still finding it difficult to follow the concept of radial circuits. If there are 10 sockets in the kitchen, does each have its own cable run to the consumer unit and its own fuse there? Do all the cables run in a single conduit of does each run separately? This would require a maze of cabling and a vast number of fuses.

I suppose the way round it would be to have one main socket and lots of extensions, but this would be less safe than our system. How would the user know which was the main socket for high current appliances? Two appliances could bring down a 16 amp fuse.

What stops them being stacked horizontally? I have seen this in the home of an electrical engineer (retired).

Would it be fair to say there were not very many AC only appliances then?

Would 13A plugs be prohibited in any rewiring?

They were also used in the older studios in Broadcasting House some 45 plus years ago. The idea was to separate the studio supply from the 'domestic' supply so you couldn't plug a vacuum cleaner into the studio supply. I seem to recall that newer studios used almost normal 13A 'square' pin plugs with the earth pin rotated for the same reason.

Yes.

No, with GPOs you can have a number of outlets on each radial.

Same with lights.

There is no all the cables.

No, even when there is more than 1 radial and there certainly normally are.

No, because there are always more than one GPO on each radial except for big stuff like the stove etc.

No it is not. The fuse or circuit breaker trips or blows when the current rating of the cable is exceeded.

The GPOs all have the same rating.

Yes and that does happen when you put two fan heaters or two high current kitchen appliances on the same radial.

I am less subtle. I have a red socket for the computer (on its own circuit). .

Thanks for the detailed explanation. Where is the logic of adding a number of sockets to a spur rather than completing the circle as a ring?

The plugs don't need to be fused and it is immediately obvious if there is any break in the radial and easy to find where that is and the wire used in the radial can have a lower cross section and so is more flexible because it has a lower current rating.