Hi All - thanks for the replies.  I've started on the inspection and the first thing is just to document "as built".  I am still puzzled by their use of 3 phase in a domestic installation.  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?  I'm wondering if there's a historical or legacy factor here.  I live in rural Norfolk and there are a lot of strange quirks here eg 2 phase supplies to remote farms.

Stephen

I am still puzzled by their use of 3 phase in a domestic installation.  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?  I'm wondering if there's a historical or legacy factor here. 

I think generally their domestic supplies are 3∅ at 32A/phase rather than say 100A single phase - but that does mean that 32A on a single phase isn't really available for any one load. It has certain advantages - less voltage drop in the N, possibly slightly cheaper wiring (say 3x 2.5mm² (total 7.5mm²) rather than 2x6mm² (total 12mm²) for the live conductors to the hob), and no parts need carry the large currents that seem to start a lot of CU fires over here. The smaller c.s.a. supply cables also mean fewer problems with high PFCs - no 16kA fudge factors for them.

   - Andy.

Thanks Andy - that's a very insightful answer.  I'll try to fit in with the locals.  There are many ways to achieve the same result.  In the end safety is the most important factor and that is achieved by a combination of physics and convention.  They all drive on the wrong side of the road here, but don't crash into each other.

Stephen

My experience is more Swiss than German however it seems that a large amount of Europe uses three phase to the house or apartment which is probably a historic thing. The typical British ‘small house’ does not tend to exist on the mainland. A large house or apartment block will be fed with 3 phase from the cable in the street (or from overhead wires) and it would then seem logical to take the three phases to each apartment.

The cost of components may be a bit higher, I would think a 3 phase main fuse and meter  would cost more than single phase but there is also less copper which may offset the difference. As Andy says will 3 x 32A be cheaper than 1 x 100A?

Another different logic is the use of a circuit per room rather than splitting lights and power per floor and the use of ring final circuits. I asked the local inspector if I could install UK 13A sockets in my house in Switzerland. His response was yes, as long as there is one Swiss socket per room. Ring final circuits and reduced CSA cpcs were not allowed.

Thanks Roger - I think I'm going down a rabbit hole here.  Why not reduced CSA cpcs?  All the breakers in this house are rated type B, which implies the use of the adiabatic equation. Another "shot in the dark" I've brought my Fluke 1651, can I get a European mains plug adaptor?  If it's not polarised, how will it work?  Should I just use crock clips and duct tape, like Apollo 13? Should I call Tom Hanks?

Stephen

Why not reduced CSA cpcs?

Primarily it's down to the 0.4s disconnection time calculation being based on a touch voltage of half mains voltage, no more - reduced c.p.c. break that assumption. In the UK we sort of presume that main bonding will reduce touch voltages to compensate, but there are a number of situations where that doesn't entirely work. They don't use UK style T&E (mostly c.p.c.s have to be insulated) - so using full sized c.p.c.s isn't that much of an issue. Full sized c.p.c.s also avoid some of the nastier problems with N-PE faults and c.p.c.s ending up carrying N currents.

   - Andy.

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.

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.