Practical advantages of 3 phase in domestic setting

murphaph

We're building a new house here in Germany and the network provider provides a 100A 3 phase (so 32A per phase) supply as standard (has been the case here for decades now). 250A is available for a small bit extra (couple of hundred quid but still seems like overkill).

So I know my heat pump's motor will run slightly better on a 3 phase supply but after that I'm stumped.

What would you do differently if 3 phase was available as standard in Ireland? Beyond providing a couple of 3 phase sockets in the garage for potential 3 phase devices (which we won't be building for a few years) I can't think of anything. Inside the house itself the oven gets all 3 phases but only to evenly distribute the heavy load across all the phases, not because it particularly needs it like a larger motor, but apart from that I can't think of any other obvious use case for 3 phase...any ideas?

skallywag

Asked myself the same question, I also built in central europe and have 3 phase sockets. I've no idea what to plug into them though, although I do admire the socket itself from time time :-)

Bruthal

murphaph wrote: »

We're building a new house here in Germany and the network provider provides a 100A 3 phase (so 32A per phase) supply as standard (has been the case here for decades now). 250A is available for a small bit extra (couple of hundred quid but still seems like overkill).

So I know my heat pump's motor will run slightly better on a 3 phase supply but after that I'm stumped.

What would you do differently if 3 phase was available as standard in Ireland? Beyond providing a couple of 3 phase sockets in the garage for potential 3 phase devices (which we won't be building for a few years) I can't think of anything. Inside the house itself the oven gets all 3 phases but only to evenly distribute the heavy load across all the phases, not because it particularly needs it like a larger motor, but apart from that I can't think of any other obvious use case for 3 phase...any ideas?

Large motors wouldnt need 3 phase just because of load, its because single phase induction motors don't have much torqe compared to 3 phase ones, and so only small single phase motors are practical. Any over 1 or 2kw will be 3 phase. Universal motors would have more torque, but they have brushes, again only practical in small sizes.

More than 1 electric shower could be fitted without having priority units, although it would need more than 32A per phase.

Normally we would say a 100A 3 phase supply is 100 amps per phase I would say. But that's neither here or there for describing the supply capacity here.

Many, If not most houses here have a connected load much higher than the connected capacity. 3 phase would help that.

murphaph

Bruthal wrote: »

Normally we would say a 100A 3 phase supply is 100 amps per phase I would say.

I think that's possibly because in Ireland the 3 phases are normally "split up" along a road so neighbour 1 gets phase 1, neighbour 2 phase 2 and neighbour 3 phase three and back to the start.... right? (so in Ireland each phase needs to be beefier than here because you only get one phase and it needs to do everything). The splitting of the load here is done inside the consumer premises, so my cellar gets phase 1, ground floor phase 2 and first floor phase 3. For the "heavy hitters" like the oven, all three phases get supplied on their own radial circuit. At least that's why I _THINK_ the rating on each phase is lower over here than in Ireland. In Ireland then if you order a 3 phase supply you get the full 100A on each phase.

Thanks for the feedback guys. I'm unlikely to kick myself if I don't do any more than a standard installation (wrt 3 phase, I plan home automation via KNX so not a completely "standard" installation for the electrician but this is one less thing to have to consider by the sounds of it).

2011

murphaph wrote: »

We're building a new house here in Germany and the network provider provides a 100A 3 phase (so 32A per phase) supply as standard

If you are told that you are being offered a 3 phase 100A supply that means that you are being offered a supply that has a "line current" of 100A per phase.

250A is available for a small bit extra (couple of hundred quid but still seems like overkill).

That would have enough capacity to run a small factory,

So I know my heat pump's motor will run slightly better on a 3 phase supply but after that I'm stumped.

In general three phase motors:
Cost less to buy
Cost less to run
Are more reliable
Are a simpler construction
Do not require brushes or capacitors

What would you do differently if 3 phase was available as standard in Ireland?

Me personally? It would be handy if I had a workshop.
That is about it.

I think that's possibly because in Ireland the 3 phases are normally "split up" along a road so neighbour 1 gets phase 1, neighbour 2 phase 2 and neighbour 3 phase three and back to the start.... right?

Yup.
I would have thought that the average house in Germany was the same.
When I lived and worked in Germany I never had three phase in any house that I lived in. Perhaps you are in a rural area?

murphaph

2011 wrote: »

I would have thought that the average house in Germany was the same.
When I lived and worked in Germany I never had three phase in any house that I lived in. Perhaps you are in a rural area?

I have 3 phase in my apartment here in Berlin as well (wiring dates from 25 years ago). The oven gets all 3. Everything else gets a single phase. I think it's pretty common actually.

2011

murphaph wrote: »

I have 3 phase in my apartment here in Berlin as well (wiring dates from 25 years ago). The oven gets all 3. Everything else gets a single phase. I think it's pretty common actually.

It's a big country.

zega

3 phase immersion heater

murphaph

The plan is a heat pump with 200L tank. The tank will have an immersion heater for the (hopefully rare) times when the heat pump can't supply enough energy, but the whole thing gets 3 phase anyway, so we're back to a couple of sockets in the future workshop/garage, which suits me fine....there's enough to be thinking about with the rest of the house!

SpaceTime

380 / 400 V was just considered too dangerous for domestic here and in Britain where it was 415V

It's not all that common in France either but in other parts of Europe large single phase hook ups are almost unheard of.

With proper modern RCD usage 3 phase can be safe enough. I don't think it was a brilliant idea in domestic settings when it was just protected by fuses though.

Bruthal

SpaceTime wrote: »

380 / 400 V was just considered too dangerous for domestic here and in Britain where it was 415V

It's not all that common in France either but in other parts of Europe large single phase hook ups are almost unheard of.

With proper modern RCD usage 3 phase can be safe enough. I don't think it was a brilliant idea in domestic settings when it was just protected by fuses though.

If it is taken as too dangerous, I don't see RCD usage making it all that much safer. A 400v shock won't trip an RCD unless there is also a good enough connection to earth, and that is not anywhere near a guarantee.

Anyone making contact with a phase will need a good connection to earth to trip an RCD, contrary to many believing it happens as soon as contact is made with a phase. Quite a decent shock can be felt before the level required to trip an RCD is reached.

Of course, an RCD makes any circuit much safer, but not certainly from 400v shocks.

cnocbui

zega wrote: »

3 phase immersion heater

If I had 3 phase I would put in an instantaneous hot water heater.

Bruthal

cnocbui wrote: »

If I had 3 phase I would put in an instantaneous hot water heater.

Instantaneous is more about how much volume/flow rate you want, than needing high power level. The more power, the more litres per minute at a given temperature rise. To get the flow rate of a tap would probably require a higher capacity than single phase alright though. But even having the flow rate of a shower in an instant tap, would require priority units if the house had an instant electric shower too.

3 phase heaters are simply 3 single phase elements connected in star, so a single phase supply can power them. But obviously 3 phases can supply 3 times the power of a single phase.

3 phase motors though, require the characteristics of 3 phases to work.

Risteard81

SpaceTime wrote: »

380 / 400 V was just considered too dangerous for domestic here and in Britain where it was 415V

It's not all that common in France either but in other parts of Europe large single phase hook ups are almost unheard of.

With proper modern RCD usage 3 phase can be safe enough. I don't think it was a brilliant idea in domestic settings when it was just protected by fuses though.

It should be remembered that a 400/230V three phase and neutral supply will still only have a Uo (voltage to Earth) of 230V (and 230V to neutral). It is simply U which is 400V - i.e. the voltage between phases.

So it's not really more dangerous in a house if installed correctly. Generally speaking any shock will be to Earth - the chances of simultaneously being in contact with separate phases are more remote.

2011

Risteard81 wrote: »

Generally speaking any shock will be to Earth - the chances of simultaneously being in contact with separate phases are more remote.

.....and even if that did occur there is no guarantee that the RCD would trip.

2011

cnocbui wrote: »

If I had 3 phase I would put in an instantaneous hot water heater.

It would be far more economical to heat instantaneously it with gas.
Besides there are instantaneous single phase water heaters.

cnocbui

Bruthal wrote: »

Instantaneous is more about how much volume/flow rate you want, than needing high power level. The more power, the more litres per minute at a given temperature rise. To get the flow rate of a tap would probably require a higher capacity than single phase alright though. But even having the flow rate of a shower in an instant tap, would require priority units if the house had an instant electric shower too.

3 phase heaters are simply 3 single phase elements connected in star, so a single phase supply can power them. But obviously 3 phases can supply 3 times the power of a single phase.

3 phase motors though, require the characteristics of 3 phases to work.

If you have an instant hot water system you don't go putting in an electric shower. In Australia I lived in two houses that had instant hot water systems which gave you whole house hot water at mains pressure and flow of 17 Bar. Only possible of course because the houses had 3 phase power.

cnocbui

2011 wrote: »

It would be far more economical to heat instantaneously it with gas.
Besides there are instantaneous single phase water heaters.

Some years ago I inquired about getting a single phase instant system and was told it wasn't practicable without 3 phase.

machiavellianme

Would 3 phase supply be of benefit to fast charging an electric vehicle?

Bruthal

2011 wrote: »

.....and even if that did occur there is no guarantee that the RCD would trip.

Most shocks probably won't trip them, I've tripped them through providing unintentional paths. Its a fairly nasty shock felt before they go. Always contact with phase and earth in one hand or hand to hand

They never trip through contact with a phase, if the only other contact is feet on ground, unless you are bare feet on wet soil, or knee deep in wet concrete, or similar. No chance it will happen in shoes indoors.

2011

cnocbui wrote: »

Some years ago I inquired about getting a single phase instant system and was told it wasn't practicable without 3 phase.

It can be done.

In Australia I lived in two houses that had instant hot water systems which gave you whole house hot water at mains pressure and flow of 17 Bar.

Bar is a unit of pressure, not flow

SpaceTime

I'm not sure why some countries limit the possibility of large single phase supplies though.

I lived in an apartment in Spain and your choice was single phase 16 amp or 3 phase 16 amps per phase.

I think it adds a lot of unnecessary complications to wiring. The only advantage in Spain was that it's useful for large air conditioners with big 3 phase motors.

The a French seem to now mostly use high power single phase same as we do.
Although where electric space heating is used (was very common due to notions of cheap nuclear power) they tend to use three phases and split the load. Nothing (except occasionally the cooker) actually connects to 400V and they usually keep the phases very separated with each phase +N having an RCD across it as well as having a three phase RCD across everything (mostly for fire safety though as they normally use TT earthing)

Bruthal

cnocbui wrote: »

If you have an instant hot water system you don't go putting in an electric shower.

In Australia I lived in two houses that had instant hot water systems which gave you whole house hot water at mains pressure and flow of 17 Bar. Only possible of course because the houses had 3 phase power.

Instant hot water can consist of an under sink unit. Not just high power systems. It would be hard to say something is only possible on 3 phase.

The characteristics of 3 phase are required for 3 phase motors. Not for heating elements though. It is possible to supply hundreds of amps on a single phase to a premises. Its just more practical to spread it over 3 phases.

You can have 17 bar with not much flow too, as a matter of interest.

cnocbui

2011 wrote: »

It can be done.
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There seems to be a bit of a misunderstanding in terms of scale here. An electric shower is not a full-house hot water heater capable of heating mains pressure water. The systems I had in mind are 36KW and need 3 phases at 50A each. http://www.westsidewholesale.com/stiebel-eltron-tempra-36-plus.html

Bar is a unit of pressure, not flow

I know. The sentence was was not perfectly constructed.

cnocbui

Bruthal wrote: »

Instant hot water can consist of an under sink unit. Not just high power systems. It would be hard to say something is only possible on 3 phase.

The characteristics of 3 phase are required for 3 phase motors. Not for heating elements though. It is possible to supply hundreds of amps on a single phase to a premises. Its just more practical to spread it over 3 phases.

You can have 17 bar with not much flow too, as a matter of interest.

Link for a domestic 36 KW 150A single phase domestic appliance please.

Of course you can have 17bar with a low flow rate, but in Australia, it isn't a low flow rate. I could just about get a jet out of a garden hose clear over my house.

2011

cnocbui wrote: »

There seems to be a bit of a misunderstanding in terms of scale here.

There is no misunderstanding. My reply about instantaneous water heating was in response to this post.

An electric shower is not a full-house hot water heater capable of heating mains pressure water.

In Ireland it would be insane to consider doing this electrically because it is so uneconomical. Plenty of people do this with gas for a fraction of the price.

The systems I had in mind are 36KW and need 3 phases at 50A each. http://www.westsidewholesale.com/stiebel-eltron-tempra-36-plus.html

This is not financially viable for a domestic installation.
Do the maths and compare the cost to gas.

Of course you can have 17bar with a low flow rate, but in Australia, it isn't a low flow rate.

It is easy to have a descent flow rate and plenty of pressure with a pump if required in any country.

SpaceTime

A french sparks explained to me that the reason for 3 phase was because early electrical installations in the early days of the 20th century were often 10 or 16amp single phase. So rather than rewire, they often just added extra phases to serve other appliances or parts of the home. This became the established way of distributing loads.

France in particular has moved much more towards the Irish or British way of doing things with large single phase hook ups for homes as the preferred option where the local distribution wiring is suitable. The main reason is that is just simplifies wiring and eliminates a lot of risky DIY jobs that three phase can result in!

The French also used to have things available like 3 phase washing machines in the 1950s to 1970 and three phase dryers. They are in reality just multi heater single phase but they were popular when people used to do a lot of boil washing in the old days.

Appliances these days across Europe are all very standardised and all just plug into a 13 or 16 amp socket.

You'll still find 20 amp and 32amp single phase sockets in some French garages and utility rooms too which were used for old high power dryers in the 60s and 70s

Cookers are usually plugged into either a 20 or 32A single phase or else a three phase socket rather than using switches and hard wiring. You're supposed to unplug the cooker for maintenance and cleaning.

They've a range of national standards for domestic sockets beyond the normal 16amp ones and don't use industrial style connectors for stuff like this. They're quite big bit neat enough to put into a cupboard etc

Also they're using RCDs on everything nowadays not just sockets. A larger home typically has an RCD for each row on a 3 or 4 row board and you scatter the lighting across all rows to avoid plunging the place into darkness when an RCD trips.

cnocbui

2011 wrote: »

There is no misunderstanding. My reply about instantaneous water heating was in response to this post.

That was a post where I said an instant system, which is not the same as an electric shower - which is an electric shower.

In Ireland it would be insane to consider doing this electrically because it is so uneconomical. Plenty of people do this with gas for a fraction of the price.
This is not financially viable for a domestic installation.
Do the maths and compare the cost to gas.

I believe the OP is in Germany.

A fraction? Doing the maths I get 47Kg Propane bottles works out at 17.3c per Kwh. I am paying 16.5c per Kwh for electricity.

(worked out at €105 for 47kg Propane where the energy density is 12.9Khw/kg)

You are right it's not economical in Ireland when the ESB charge north of €20,000 to give you 3 phase.

It is easy to have a descent flow rate and plenty of pressure with a pump if required in any country.

I have a Stuart Turner 3 bar pump and I would call that acceptable.

Bruthal

cnocbui wrote: »

Link for a domestic 36 KW 150A single phase domestic appliance please. .

Well in post 12 you said you would get an instant water heater.

I simply posted that an instant water heater can be single phase.

You then upgrade your instant heater to a system in post 17.

Bruthal

cnocbui wrote: »

That was a post where I said an instant system, which is not the same as an electric shower - which is an electric shower. .

2011 has linked the wrong post by the look of it. Post 12 clearly says you would get an instant water heater. There lies the scale problem. Posters can only post opinions on info provided.

murphaph

I just checked and apparently you can buy 400v domestic washing machines and tumble dryers here in Germany. They are like the hobs/oven...can be supplied either 3 phase or single phase, depending on what you have.