9 ms·
How many residential appliances benefit from three phase, and is the benefit outweighed by the additional cost of more copper for the additional wires? For exa
by Kirby64 3y ago
How many residential appliances benefit from three phase, and is the benefit outweighed by the additional cost of more copper for the additional wires?
For example, a common big motor that needs a starter capacitor is a HVAC unit. Usually 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. By comparison, starter caps are quite cheap. $20 for a HVAC sized one. That also isn't counting any of the costs of three phase infrastructure for breakers etc.
That also isn't even counting that many appliances are moving to inverter based technologies that don't utilize induction motors at all, such as induction hobs. Or, many appliances with no benefit from extra phases (resistive heating devices such as ovens, dryers, toasters, etc).
Seems to me that the tradeoff is worth it.
- loandbehold 3y agoTransmitting same amount of power at higher voltage requires LESS copper.
- deleted 3y ago[deleted]
- kelnos 3y agoBut you need an extra conductor, no? Doesn't that make up for the reduced amount of copper in each one?
- nullc 3y agoFor 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.
- japanuspus 3y agoI 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).
- deleted 3y ago[deleted]
- Mvandenbergh 3y agoIn 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.
- briHass 3y agoMany 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.
- jonhohle 3y agoOthers 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.
- jrockway 3y agoDon'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.
- lfowles 3y agoIt was only present on the high end when we were replacing our system in 2021.
- lizknope 3y agoI 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.
- kelnos 3y agoUnfortunately 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.
- amluto 3y agoLittle 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.
- Faaak 3y agoOn the contrary, more phases = less copper. Example of appliances: HVAC, induction heaters, boilers, car chargers, solar panels inverters, ...
- wyager 3y agoThree phase and high voltage are both more copper-efficient.
- dijit 3y ago> 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.
- deleted 3y ago[deleted]
- Kirby64 3y agoLow 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).
- quickthrowman 3y agoThere 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.
- brianwawok 3y agoWhy 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.
- thsksbd 3y agoIt 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.
- sidewndr46 3y agoinverter technology is always an induction motor. No one runs an inverter to run a universal motor.
- dreamcompiler 3y agoBrushless 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."
- user2342 3y ago> 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.
- Kirby64 3y agoYou 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.
- bluGill 3y agoMost 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)
- timc3 3y agoThe 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.
- 3y ago
- bell-cot 3y ago> ...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...
- deleted 3y ago[deleted]
- Kirby64 3y agoI'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.
- timc3 3y ago3 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.
- gambiting 3y agoWell, 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.
- muxator 3y ago> 60amp draw at 220V You are very luky! The standard installed power for residential use in Italy is 220 V, 3.3 kW.
- rekoil 3y agoSingle-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.
- muxator 3y agoYep. 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.
- gambiting 3y agoDo Italians not use electric kettles?
- rekoil 3y ago> 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.
- adev_ 3y ago> 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.
- fomine3 3y agoTo 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 want more 200V home appliances, like 200V 3kW kettle!
- Kirby64 3y agoI'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.
- colinsane 3y ago> 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.
- ThePowerOfFuet 3y agoResistive dryers aren't common in Europe; they are mostly condensation dryers which use much less electricity.
- redeeman 3y ago> 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
- Maxion 3y agoI 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.
- kails_ 3y agoIn 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... .
- zerof1l 3y agoOne 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.