I read this comment as implicitly assuming two phases to require less copper than three. In reality, the total copper cross-section needed to transfer power in a multi-phase system _decreases_ with increased number of independently wired phases (all else being equal).

Transmitting same amount of power at higher voltage requires LESS copper.

But you need an extra conductor, no? Doesn't that make up for the reduced amount of copper in each one?

For three phase vs single face, the amount of copper doesn't go up since the current is shared across the additional conductors-- generally the amount of copper required is actually lower due to power factor improvements.

However, for low capacity hops the cost of additional insulation and extra copper needed to achieve ampacity (for worst case fault currents-- the cable must have higher capacity than the breaker so the breaker trips first and with 3ph you have three over-provisioned conductors instead of two) may make it worse off.

In many places (but not the US because of thermostat standards) HVAC systems are now typically inverter driven as well so that does remove some of the advantages of three-phase since any individual load is single-phase anyway.

Many HVAC systems in the US also use inverter compressors now. The efficient units (which includes most minisplits) are inverter. The efficiency requirements of the recent government subsidy program pretty much requires an inverter.

Others have made the comment about lower current requirements at high voltage, but from a maintenance perspective, that $20 capacitor is a common failure part. Calling an HVAC repair company to diagnosis, parts, and labor it costs around $200 for anyone not electrically minded. Over the life of an AC unit, starter/run caps might have to replaced twice.

Even if an extra conductor in the line was a few hundred dollars, I’d rather have one less common failure point. In AZ AC is effectively required in the summer. AC outages are similar to winter furnace outages in northern areas. I have extra caps ready to deploy (we lose a cap about every 3 years across multiple units) but have never needed to unexpectedly replace copper.

Don't more modern AC units use VFDs that can run the compressor at arbitrary speeds, which is an improvement over both fixed 3 phase power and a starter capacitor? Maybe this tech hasn't made it into the house-sized units yet, though.

It was only present on the high end when we were replacing our system in 2021.

I just replaced one of my two HVAC units with a variable speed compressor. It cost a lot more than the single or 2 stage units but it is more comfortable, uses less electricity, and runs at "low" to dehumidify longer.

Unfortunately these more modern units are still stupid expensive (in the US) compared to the older style. Unclear why; probably some sort of shenanigans with the HVAC manufacturing companies.

Little variable-speed units sold as ductless minisplits are fairly inexpensive in the US. They’re especially reasonable if you actually use them in a ductless configuration, because you don’t have to install ducts.

The fact that they might have a higher list price than a conventional single-speed outdoor unit and indoor evaporator coil is a red herring, as the conventional units can’t do anything on their own, and they need a furnace and a fan added to be useful.

VFDs / "inverters" are happier on 3 phase as well, because the input rectifier caps can be much smaller. Whereas with single phase they have to be large enough to store energy for riding out the zero crossings of low power delivery.

Just had to have my apartment's AC capacitor replaced last week.

My point isn't that the single individual wire to your HVAC is $100 vs. a $20 cap, though. There is likely hundreds or thousands of dollars of additional infrastructure needed to handle 3-phase input to a house. You have breakers, busbars, the transformer into the house is different, and on and on.

I agree that less failure points is nice, however you have to consider the tradeoff. Is it worth $100? Probably. What about $1000? $2000? If it's $2000, why not just get a more efficient inverter based one, which doesn't have a starter cap in the first place?

> There is likely hundreds or thousands of dollars of additional infrastructure needed to handle 3-phase input to a house. You have breakers, busbars, the transformer into the house is different, and on and on.

Split-phase system and 110V are currently more expensive in term of infrastructure.

The distribution itself is done in 3-phases power, even in the US. The conversion to 110V and split phase is done in the last mile as close as possible to the termination point to limit losses. You have to have tiny power transformers everywhere and this has a significant cost.

At the opposite, end-to-end 400V three phases system requires to have only one large transformer by Area. Generally directly connected to High Voltage (20KV in Europe).

This isn't any different in the US vs. in Europe. Split phase is done at the last mile, just as it ought to be done in Europe for 3 phase power. I highly doubt entire neighborhoods or districts are serviced with a single extremely large 400V 3-phase transformer in Europe.

Standalone houses usually have multiple houses connected to one single transformer. How much depends on density of the houses. For apartment buildings and other dense power needs, there's high voltage directly into the complex, then it's stepped down within the complex to meet the needs.

US distribution transformers are around 50 kVA, in the EU they are more like 300-1000 kVA, so they can power 10-20x more homes per transformer.

Instead of those little pole-mounted transformers that are common in the US, we have one of these buildings with a large transformer for each neighborhood https://dms-cf-08.dimu.org/image/032ykUus1ixX?dimension=1200...

https://electrical-engineering-portal.com/north-american-ver...

Very interesting. Seems like that works much better as the power demand per house in the EU is lower, and the higher voltage gives you a bit more leeway. Frankly, I would be concerned about voltage drop for the far houses... even 400V is going to have some pretty beefy voltage drop under load unless the conductors are enormous.

> I highly doubt entire neighborhoods or districts are serviced with a single extremely large 400V 3-phase transformer in Europe.

They do currently.

I can at talk for the French and Swiss system.

- Entire neighbourhood are served by a single 400V 3-phase transformer. - For critical infrastructure, you do have sometimes two transformers in redundancy on the same local loop in case of failure on one.

There is no need for the pole type of transformer everywhere in the street with double layers of cable like in Japan or in the US.

One note regarding the pole transformers: in many parts of the US they've migrated to underground cabling and larger transformers. My neighborhood has that, and we have about 1 transformer every 4 houses or so. No idea how big the transformer is from a kVA rating, but pretty much every house has 240V/200A service, so they must be pretty large. The transformers themselves are approximately 3' x 3' x 3' and enclosed in a box at the front of certain yards.

> My neighborhood has that, and we have about 1 transformer every 4 houses or so.

You might find that interesting:

https://data.enedis.fr/pages/cartographie-des-reseaux-conten...

This map references all transformers and distribution lines for the french network nationwide for terminal loops. These are open data: Enedis is a the public operator.

"Poste" is the French Jargon for transformer. BT is for low voltage. HT is for anything >1000V.

Like you will see yourself, the density of transformer is of the order of 10x less than in the US/Japanese model.

On the contrary, more phases = less copper.

Example of appliances: HVAC, induction heaters, boilers, car chargers, solar panels inverters, ...

Three phase and high voltage are both more copper-efficient.

> How many residential appliances benefit from three phase

I know of at least one, but I am ignorant of many other things and this just comes from my understanding of AC motors but: Any directly connected AC fan will have enormous benefits in terms of performance and efficiency with three phase.

Low current devices such as AC ceiling fans use so little current that the wire gauge is largely based on the minimum sizing for code standards. At least in the US, you can't put anything smaller than 14 gauge (AWG) in walls. Maybe in Europe they allow much smaller gauge, in which case maybe it makes sense... but usually there are minimum requirements for wiring since it becomes a structural issue (i.e., too thin of wire will break easily when pulled).

There is no benefit to performance or efficiency with a single-phase motor vs a three-phase motor.

Controlling the motor with a VFD is how you increase the efficiency and performance of a three-phase motor, simply being a three-phase motor provides no efficiency benefit other than you can use slightly smaller conductors to power the motor.

Why are large industrial motors three-phase? I almost always see large industry getting three-phase, which I assumed either gave more power or more efficiency.

It has nothing to do with efficiency (do the math on the conductor gauge and it all mostly cancels out) or power (idem) but the types of motors used (squirrel cage I believe).

The problem is getting the motor to start spinning. You cant start all motors on just one or two phases. And if a motor isn't spinning, it's essentially a short.

No, very large single-speed industrial motors are synchronous motors, not squirrel-cage (induction). These motors cannot start spinning on any number of phases: they can only run at the synchronous speed (which is dictated by the power line frequency and the number of poles in the motor). And it's not a short; it just doesn't run at all if you supply power to it; it only works once it's at the synchronous speed. These motors are used because they're the most efficient type of AC motor. Induction motors have "slip" of around 3% IIRC.

Basically what the sibling comment said, it’s easier to start a three-phase motor, and a three-phase motor will also run more smoothly as it is powered by 3 sine waves 120 degrees out of phase with each other which provides constant power; versus a single-phase motor being powered by a single sine wave that outputs no power at the middle of the sine wave with two power peaks, which doesn’t run as smoothly as three-phase power with no points of zero power output.

inverter technology is always an induction motor. No one runs an inverter to run a universal motor.

Brushless DC motors are always driven by inverters. They aren't usually sinusoidal inverters, and these things are more accurately called digital electronic pulse modulators, but they're often advertised as "inverter-controlled."

> How many residential appliances benefit from three phase, and is the benefit outweighed by the additional cost of more copper for the additional wires?

Three phase wiring is so ubiquitous here, there is nearly no additional cost.

You can't just say there's no cost because you don't see it. You don't have the option, so of course there's no way to tell price differentiation. I'm talking purely of raw material cost though. By adding a 3rd load conductor, you inherently add wiring cost and complexity, which should result in cost to the consumer.

It may be offset, as others point out, by power delivered being higher (and thus, wire gauge can go down) when running 3 phase... however that will largely depend on the load.

Most people have so few things in their house that would benefit from 3 phase that the cost isn't worth it. That extra wire isn't cheap, even if you downsize them all you still pay more. And as others have pointed out modern motors are (slowly) switching to using a VFD to generate 3 phase so there is even less need (in fact in industry a lot of equipment is switching to a VFD even though 3 phase is wired to the machine)

The cost is insignificant.

I have monitoring on all the phases on my house (in Sweden) and I can charge two electric cars, run the heating in winter, run the washer and drier and cook with two ovens a microwave and the induction hob at the same time and everything just works.

Things on three phase in my home: swimming pool, sauna, induction hob, electric car chargers, heating system and I have sockets to plug-in welding and other power hungry equipment. The rest is split on the phases. I can’t remember whether my solar system supplies on three phases or not but I think it does.

You have it so they use it, but single phase will run it all just fine. The pool pump and welder can benefit from 3 phase, but for the pool pump the benefit is marginal. For the welder a modern inverter welder is better yet.

We can get 400v 3phase inverter welders here.

Yes, we have it so we use it - for sure.

The pool pump on 3 phases seems slightly more efficient when I compared them last time. The pool is also being fitted with a heat pump inverter, which doesn’t need 3 phase.

Yeah, but how many amps? What really matters is what your total available wattage is. In the US, 240v@200A (48KVA) is not uncommon. My 1979 house and every other one on the block has that, and that was assuming fossile fuel heat.

That can easily support all the things you listed and do it for a 2500 sq ft house, based on the overly conservative and outdated US NEC lead calculations.

Sure it’s 3 phases of 32 Amps. I can request more, but it’s not required.

> ...the copper to run those is extremely expensive, on the order of hundreds of dollars. Adding an additional wire may add an additional hundred dollars or more...

Vs. checking a couple commodity pricing web sites - copper is currently ~$3.85 per pound.

I really doubt the motor of any "residential" HVAC unit is heavy enough for that "hundreds of dollars" to actually pan out...

I'm referring to the cost of the wiring, not raw copper stock price. Also, I mean the cost of the wire from the breaker panel to the HVAC unit. On average, I'd assume that the wire run is at least 50 feet. 100 feet wouldn't be unusual. 100 feet of single-wire 10 gauge THHN (enough to run most HVAC units here) would be ~$60. That also doesn't include any additional cost by upsizing certain things (conduit) that may add.

To note, as mentioned, copper is not the only cost here. You also need another pole to your breaker, which adds cost. Plus busbar upgrades. And more.

3 phases is cheaper than single line for delivering a houses power. You can get away with 3 smaller cables than the larger cables needed for 110V or 230V low voltage single phase at a particular amperage.

The cost of termination of 3 phases is insignificant compared to the cost of the rest of an electrical system in a modern home.

It’s the better system.

Well, here in UK nearly all residential properties have only a single phase supply - it can actually be really limiting nowadays. Some older properties are only wired for 60amp draw at 220V, meaning you can really only have an electric shower and an oven on at the same time and that's it, you've gone over the limit. People are finding it more and more as electric cars are getting popular and turns out fitting a 32amp(7.2kW) charger on a single phase 60 or even 80amp supply is sometimes not feasible depending on what else you have in your house already. Continental setup is far superior to what we have here for this reason.

> meaning you can really only have an electric shower and an oven on at the same time and that's it, you've gone over the limit

What's the deal with your electric showers anyway? Surely it's more efficient to heat in a central location and distribute both a cold and a hot water circuit through the building...

Probably talking out of my ass, it's just so weird and I haven't seen it anywhere other than in the UK.

Storage hot water is actually quite inefficient.

On-demand heating has the advantage that there is no thermal loss due to keeping a large amount of water (plus piping) hot 24 hrs a day.

Plus water is not wasted in waiting for hot water to arrive each time a tap is switched on.

Back in the days of Coal-fired power stations, people were encouraged to use storage hot water systems which were automatically switched on at night, so the the power stations could continue running because of the large base-load power demand.

However the modern Solar/wind generated power systems are the opposite, they much prefer loads which are only on during the daytime.

Even with heat loss by tank, It's x2-x5 efficient if it uses hear pump water heater. Also storage system works great when solar generators are active.

On-demand HWS can use heat-pump technology if required. Even tiny refrigerators use a heat pump. If they aren't widely used, it's because the savings are too small to warrant it.

Regarding solar HWS: The cost of heating panels, piping, and installation, has meant that they are fast disappearing from the market. It's better to add a few extra solar electric panels and use on-demand HWS, either with battery storage or via grid connect.

I've just been down this route with a new solar electric plant. I had originally assumed that Solar HWS would be included, but after doing the calcs, have abandoned the solar heating panels and instead opted for a few more solar electric panels plus extra Lithium batteries. It means I have a lot more storage that can used for many different purposes.

Refrigerators are similar to tank system, rather than on-demand hot water system. With smaller heat pump, tank is needed because it can't heat water immediately. Refrigerators have small heat pump so that's similar thing. Both should have good insulation.

Heat pump heater can be run when solar panel generates so much energy (energy price is low). That's a similar thing as batteries for energy use time shift.

You do usually, but with a gas combi boiler. Electric showers aren't that common in the UK either (23 years here and never seen one in person; but had never heard of them before moving here...), and usually a hack when putting a shower somewhere that didn't previously have plumbing.

Electric showers are a result of low quality, cheap-as-possible housing.

I've seen them (my parents have one) in the UK, and lower income countries in South America, Asia and Africa.

Historically hot water in most houses in the UK came from a gravity fed tank in the attic. This means low pressure. If you wanted a high pressure shower, your options would be to replace the gravity fed system with a cold water pressure system (which can be expensive and might also involve disruptive relocation of pipe work) or to just fit a cold water fed power shower.

> 60amp draw at 220V

You are very luky! The standard installed power for residential use in Italy is 220 V, 3.3 kW.

Single-phase 16A? That's the standard? My tiny apartment homelab probably uses at least a third of that (I should measure its consumption actually...).

Said 50m² apartment has 16A triple-phase installed, but the breaker box is wired to be capable of safely drawing up to 63A triple-phase from the grid if I needed it.

Yep. You can obviously upgrade to 4.5 and 6 kW (still single phase, I think), or go three phase. Single house probably do that. But I'd be surprised if the apartments had more than 3 kW installed.

This results in a big payoff for efficiency, however: high efficiency AC and heat pumps for water go a long way in increasing how much you can do on so much little power.

Do Italians not use electric kettles?

Only those that consume 3 kW max :)

Jokes aside, I think that this ends up incentivizing an efficient use of energy. That's not so bad after all.

I mean sure, but there are certain appliances(like kettles) which really can't get any more efficient, so if you want to boil some water......3kW overall limit for the entire apartment is seriously limiting. Like, if someone is boiling water and another person uses a hair dryer, it will blow fuses?

My place was renovated about decade ago and has 3x25A... And I don't have anything special like Sauna and circuits are pretty much original...

> How many residential appliances benefit from three phase

Induction hobs, saunas, EV chargers, to name some.

> and is the benefit outweighed by the additional cost of more copper for the additional wires?

Additional cost? You don't run that many 3-phase circuits, so the cost is negligible, and your 110V circuits require substantially higher current than ours (meaning thicker wires) so if anything I'd guess the cost for wiring a US home is on average higher than a European home.

> How many residential appliances benefit from three phase

You can add: Heat pump, electrical water heater, well pump, ovens.

I lived in both Europe (400V) and Japan (100V).

In Europe I do have an EV charging station 3-phase power with 22KW capacity at home. It does not requires anything special in term of cabling.

And it is enough to reload a Tesla in 4-5 hours, it makes EV ownership a lot easier.

Doing that with the 100V power-grid Japan is simply impossible. Most grid operator will refuse to connect 3 phases power to individuals.

To fair comparison, it's 3 phase 400V vs single phase 200V. I agree Europe system is better but it's not worth to change with huge costs.

Modern heat pumps in Japan with inverter is just fine with 100V or 200V for home, even for cheaper coolers. 200V hear pump electrical water heater (with tank) too.

Most houses sign up only up to 6kW or 10kW electricity, so EV charger will become a problem for family that has multiple EVs, but they will be fine with slower charging at night in most cases.

It's pain that common 100V ovens works poorly. 100V Washer dryer works barely okay thanks to efficiency.

I'm talking about appliances that benefit specifically from three phase because of the benefits of induction motor driving. Water heaters, ovens, EV chargers, and many other things specifically do not benefit from this. The only thing you get is power density by effective 400V output from 3-phase 240V.

Obviously 100V would be terrible for high power stuff. I'm not suggesting that. But, 240V split-phase is more than sufficient for the vast majority of residential appliances, including EV charging.

> Water heaters, ovens, EV chargers, and many other things specifically do not benefit from this. The only thing you get is power density by effective 400V output from 3-phase 240V.

They do too. You have lower current intensity, lower cable diameter, lower losses.

For EV charger it is even more relevant because anything inverter based has (theorically) a better efficiency in a three phases system.

The only drawback of three phase power is currently the cabling complexity. The home electrical panel need to be careful of the phases's balance.

I specifically was referencing any benefits from induction motor drive with 3 phase. Of course you get lower current when you run higher voltage and more phases. But, again, that isn't free. You're paying for extra conductors and insulation.

Regarding EVs... I would assume that depends on the design. No EV sold in north america is even capable of being charged off 3-phase AC anyways, so it would require quite the redesign.

In the house we're currently buying there's actually an old laundry spinner (?) in the cellar, hooked up to three-phase power. The electrician mentioned that those motors basically never broke down and were far more reliable than 230 V one-phase devices. However, other concerns, like being able to put the washing machine in your flat out how many such outlets you actually have, probably phased those devices out. I'm not sure I'd consider a three-phase outlet for the rewiring now. The stovetop of course gets that, and, if necessary one day, the wall box for EV charging, but there's not many appliances these days that need it.

Not sure the electricians comment is related specifically to the three-phase itself, or just to the general observation that three-phase motors are put in more industrial/commercial applications, where reliability is much more important. Pair that with residential use of commercial appliances tends to be very gentle on them (e.g., they don't get run 24/7, vs. a commercial place that would try to use them at every possible moment) and you have a recipe for a very reliable device.

I asked them whether it was specifically about that and they said yes. The appliance in question was a consumer item, just a tad older, not a repurposed industrial machine.

Surely we should also factor in amortized costs of injuries and/or property damage due to fires with both systems.

> is the benefit outweighed by the additional cost of more copper for the additional wires?

don’t cheap out on wiring. a few years after you move homes, you find some new hobby: woodworking, CNC or 3d printing, restoring pinball/arcade machines, HiFi audio, hosting LAN parties or just a few beefy gaming or video editing rigs, hot tubs, _whatever_. you can’t predict it, but there’s a good chance it’ll need power, and once you pass 1500 W in one area of the home you’re gonna either be playing the “semi-permanent 50-ft extension cords bridging the under-utilized circuits to the over-utilized rooms” (and shuffling those around with every spring cleaning) or paying 4 figures to rip out the drywall and rewire shit. just pay that up front: it’s not worth the hassle and if you have a decent realtor you’ll recoup the bulk of the investment come sale time.

Resistive dryers aren't common in Europe; they are mostly condensation dryers which use much less electricity.

> How many residential appliances benefit from three phase, and is the benefit outweighed by the additional cost of more copper for the additional wires?

due to the higher voltage in europe, conductors tend to be quite a bit thinner than in the US, to carry the same amount of energy. That being said, our electrical installations tend to be much beefier than most US residential, so a lot of copper is used. in Denmark for example standard for houses is to be fused at the roadside box for 3x~30A

I could get up to 3x64A in Finland if I wanted to pay for it. 3x35A is pretty common for new builds here. Older tend to be 3x25A.

In EU, there is another important aspect, that is: the fact that the suburbs are mostly composed by residential buildings with 2 or more floors, unlike the US. It's really common for every building to have 3 phase 380V booster pumps, elevator motors, central heating systems, etc... .

One example would be a cooktop and electric oven. I have one that connects to 3-phases. On the cooktop, the left and the right sides are each connected to their own phase. You can run both sides at 2,600 watts max at the same time. In the oven, there are 3 heaters: top, bottom, and one inside the fan; each connected to one of the phases. Together they can reach about 10,000 watts. The oven has a heat-up program that uses all 3 heaters to reach the temperature you've set.

Overall, it can heat things up more quickly than a typical gas or electric stove while being more efficient. And you can quickly change the temperature like with a gas stove.