Stephen Biddle said:

It must be more expensive, for no apparent advantage.   There is a hob running of 2 phases of 16 A.  Why not 1 phase of 32 A?

Certainly, the lights and sockets indoors will all be SP, but there are plenty of cookers which use TP.

If the hob uses 2 phases, does the oven use the third one?

If the hob uses 16 A for 2 'burners' that is a bit under 2 kW each, which seems perfectly reasonable.

No, single phase is more expensive to install over distance, as heavier cable is needed overall for the same KVA, as there is no neutral cancellation -  consider, if it was cheaper an you could get more  current down the same cables,  we'd have the DNOs converting to three phases into  single phase in the street ;-)

For some reason us Brits come out in something of a nervous rash over 3 phase, when it can actually be a really good idea. Not as much of a rash as the Americans however, who manage to cock it up completely by connecting the neutral onto the wrong bit of the triangle - middle of a side of a delta , instead of the centre of a star...

(pin the neutral on the transformer, a party game for blind-folded electricians)

An additional benefit of the thinner phase wires is that you can have lower fault currents for the same KVA supply. A 32A  3 phase supply  more or less replaces a UK single phase 80 to 100A could be wired in 4mm or even 2.5mm in the right installation  conditions and have a PSSC of 500A - much less of an arc flash hazard. (and the lower rated incoming fuses give a tighter energy limiting action too)

Be glad you don't see 1k3/690 3 phase here, and only 690/400 and 400/230. Germany is a fun place. (to be fair I only saw the 1k3 3 phase on one site, and it was Siemens, who are old enough and ugly enough to make up their own rules.)

Mike.

mapj1 said:

An additional benefit is that you can have lower fault currents for the same KVA supply. A 32A  3 phase supply that replaces a single phase 80 to 100A could be wired in 4mm or even 2.5mm in the right installation conditions and have a PSSC of 500A - much less of an arc flash hazard. 

When you mention that we have houses in some areas with Ipf of 10kA or even higher in central London. It leaves European electicians looking at you like you're an idiot.

It's absolutely ridiculous how high our Ipf is. I've got a TN-S supply in a residential part of a small town, and it's about 2.5kA in my house.

Madness.

You may still have a fairly high PSSC, if you live right next to the substation, just as you may in the UK, but multi KA fault currents are I think less common than here, except in industrial settings or mabye in the basement of blocks of high rise flats with their own 'trafo', or for the really tall ones, even HV arteries going up the building and then a transformers  on every 3rd or 4th floor - in the UK places like Canary Wharf do that, but it is most unusual, that had quite a lot of continental design influence.

Domestically this in turn certainly used to lead to far a more 'roll your own' approach to dis boards and without the 16kA nonsense,  no need to worry about mixing makes on the same DIN rail or adding bell transformers and other things into the (usually bigger than the UK) box (Sicherungkasten)

I dont think it has changed all that much.

Mike.