Keir Stitt said:

3kW kettles wouldn't be affected because they're only for intermittent use.

Are 3 kW kettles still available? I thought that they had been banned for being too powerful. (Yes, I do realise that an old one might still be in use.)

seemingly so - https://www.argos.co.uk/product/2137074

Wouldn't it be better/simpler just to tighten up on BS 1363 so that plugs and sockets could carry their rated current continually? The old ones with nice solid brass pins and rigid  UF plastic mouldings didn't seem to have as many problems (loose connections notwithstanding) - if they can do it for ones marked EV on the back, why not for the rest?

  - Andy.

The lower the power of a kettle the longer it takes to boil and therefore it would be less efficient.

So I don't think kettles have been included in scope of the eco design regulations. Storage heaters perhaps are. Fundamentally it takes 1cal=4.2J to raise 1ml of water by 1°C, so if you're going to do it for immediate consumption then do it as quickly as is safe and practical.

Maybe we should have a 32A socket in the kitchen and then we could boil 1l of cold water in under a minute. 

What is the wattage of the motor?

So I don't think kettles have been included in scope of the eco design regulations.

I suspect they have, but with the emphasis on being able to boil only the amount of water required (e.g 1 cup full) - rather than the old designs where it took three or four cupfuls to "cover the element". As you correctly say, limiting the power doesn't reduce the energy consumption - often quite the reverse.

   - Andy.

If this CNC machine of yours is a non portable  thing then wouldn't it be easier to power it from a 20 or 25 amp double pole isolator? That would get round all the problems of which type of plug is best and you wouldn't lose any portability if it a big heavy lump if a machine. Also south African 15 amp plugs are now rated at 16 amp although the design is the same as when it was 15 amp.  I always thought those old plugs looked capable of carrying much  more than 15 amp the plug pins are very beefy 

the plug pins are very beefy 

Although it's usually the springy socket contacts rather than the c.s.a. of the pins that's the limiting factor ... it can be quite a challenge to get a decent reliable contact area, especially on a curved surface (and one where the radius of the curve may reduce slightly over time as the pins wear) - one of the design features of the 13A system was flat pins is that the flat contact areas provided better and more reliable contact.

   - Andy.

No, they are still available - I got one not too long ago.

Would hate to have to downgrade when I'm cooking...

Keir Stitt said:

Of course I can risk assess a departure from 553.1.201 given that interlocking offers a greater level of safety than shutters. 

Interlocked outlets may be provided with either an interlocked switch or an interlocked isolator.

Interlocked isolator versions used to be quite rare and expensive, but now are more readily available as some special locations (e.g. Section 708) require them. Best to ensure they have the 'isolator' symbol on them.

Another consideration, though, is that socket-outlets to BS EN 60309 series (including interlocked isolator types) I understand are Overvoltage Category II ... BS 1363-2 shuttered outlets are Overvoltage Category III ... so, do interlocked industrial socket-outlets (even with the isolation function) always offer 'equivalent safety' to a shuttered socket-outlet to BS 1363-2?