Is 3-phase power in any way better than split-phase power in a residential setting?

Question

My understanding is that in the US (and Canada?) residential units receive split-phase 120V/240V power meaning the voltage between two phases is 2x the line-to-neutral voltage. Here in Europe residential units receive 3-phase 230V/400V power meaning the voltage between two phases is only 1.7x the line-to-neutral voltage.

Is there a reason for the European arrangement? If Europe also used split phase power then we could get one of these:

1. 200V/400V power meaning most appliances would be safer due to the lower line-to-neutral voltage while power-hungry appliances (like stoves) could still get the same 400V as before.
2. 230V/460V power meaning power-hungry appliances (like stoves) could get 60V higher voltage without there being a need raise the line-to-neutral voltage so most appliances would be just as safe as before.
3. Some intermediate option between these.

To a layman like me 2x just seems better than 1.7x. Surely no one has an AC motor at home that would actually need all 3 phases? Is there some reason for delivering 3-phase power to households I'm not seeing or what is the reason for the European arrangement? Is it just an artifact of history that's too costly to change now?

Answer 1

Three phase power is better in almost every way except the costs of the wiring to your premises, because it needs more conductors. In Europe thinner conductors due to the voltage, so the comparison is not direct.

Three phase power for residential in the Netherlands is 4 wires (L1-L2-L3-N) and an earth rod per house. This gives you 230V L-N and 400V L-L. Good for almost 17 kW with a typical 3x25A fusing on just 6mm2 cabling (10 AWG).
This is the default for new houses, and the wiring is there since 1960, they just never installed the other two fuses.
There is a HV-LV transformer per suburb, not per house.

Compared to 17 kw single phase which would give you a 1x75A service. That's a range where wiring and protection circuits become significantly expensive.

It also provides you with the possibility of running three phase motors, which is especially beneficial with high performance HVAC systems (which we use also for heating) or people with small workshops in the garage. Some big houses also have pools and flow-through shower heaters or sauna's that reap the benefits of this. These things require lots of power.

Also the possibility to put those heavy loads such as induction cooktops or PV inverters on all three phases balances the local grid preventing voltage sags.

I forgot the most high power load: EV-charging.

We can get up to 3x80A, but most people are on 3x25A or 3x40A. Which costs you 250 or 1000 euros per year. More than enough power, just don't turn everything on at once.

Answer 2

120V is not a practical voltage for the more powerful household appliances, which is why 120V countries also get 240V split phase. Since most houses there have both 240V and 120V, manufacturers can sell powerful appliances in 240V and not bother to make 120V versions.

In 230-250V land, there is no need for that, so all appliances use 250V. And since few houses have three phase, no-one bothers to make three phase versions of most household products, unless it's justified by the power use of the appliance.

Split phase creates a strange situation in 120V land where you get all the annoyances of three phase power:

• More wiring
• Different, incompatible sockets
• Got to balance the loads

...without the main advantage of three phase, which is that, if the load is balanced, power flows continuously instead of 100-120 times per second. This means, according to Wikipedia:

As compared to a single-phase AC power supply that uses two conductors (phase and neutral), a three-phase supply with no neutral and the same phase-to-ground voltage and current capacity per phase can transmit three times as much power using just 1.5 times as many wires (i.e., three instead of two). Thus, the ratio of capacity to conductor material is doubled.[9] The ratio of capacity to conductor material increases to 3:1 with an ungrounded three-phase and center-grounded single-phase system (or 2.25:1 if both employ grounds of the same gauge as the conductors). This leads to higher efficiency, lower weight, and cleaner waveforms.

(Note your 1.7x factor is wrong).

Basically, three phase would be better for everything, including switching power supplies because it gets rid of most of the big smoothing caps. However it is not practical to use at low power, due to the extra expense in wiring, plugs, sockets, PFC units, transformers, assorted electronics, etc.

However, if you get a big motor, or a big motor with a variable frequency drive (most commonly known as "heat pump") then three phase is a much better option. You just don't run a 10kW electric motor without three phase, and if you do, it's damn ugly.

Answer 3

I am not sure why so much focus on the voltage difference. That is missing the point. In three phase power you use all three phase wires to deliver power so you can't ignore that. So using a metric of 1.73 for the line-to-line (or line-to-neutral voltage) for three phase power is wrong because by using 1.73 you implying that all you did was connect a device up to only two phases of a three-phases supply thus forcing it to run as a single phase at the same current as the split phase. You can't ignore the other phase wires and the currents in them.

NOTE: As a layman you will need to read up the voltage and current measurements in wye and delta systems; Namely the difference (and equivalence) between:

• phase voltage vs line-to-line voltage vs line-to-neutral voltage
• phase current vs line current

The phase value definitions are the same between wye and delta because they are internal to the wye or delta. However, the structure of the delta or wye may not make these phase values directly measurable from "outside" which is what line values are. Therefore line values have different, often swapped, relationships to the phase values depending on wye or delta.

It is most obvious examining a 4-wire delta. A wye has the neutral point "invisible" and not physically accessible even if you are looking inside the delta; You can only mathematically access it.

The main reason you need to know these is that power calculations need to be consistent in the voltage and currents used. No mixing inconsistent definitions of voltage and current in your power calculation.

You will want to refer to a wye and delta schematic (\$\phi\$ is for phase):

WYE:

\$V_\phi=V_{L-N}\ne V_{L-L}\$

\$I_\phi=I_{L}\$

DELTA:

\$V_\phi=V_{L-L}\ne V_{L-N}\$

\$I_\phi\ne I_{L-L}\$

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Thus, the same phase voltages and phase currents, it is 2VI for split-phase vs 3VI for three phase. It is also the same result if you use line currents and line-to-line voltages. (Note how I am using only internal values or external values together. Line-to-neutral is not explicitly mentioned because although it is sometimes equivalent to some of the values used, it is not explicitly always internal or external between wye and delta and I do not want to divide things up by that because it would get confusing).

Therefore, for 50% more copper you get 50% more power carrying ability, less peaky power delivery, and a naturally rotating magnetic field.

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"Surely no one has an AC motor at home that would actually need all 3 phases?"

I want a three phase bench grinder for my garage but I can't get one because I don't have three phases. Or a table saw. Power delivery is less peaky in three phase and motors are simpler, run and start more smoothly while being simpler (cheaper and more reliable).

Answer 4

There are a few rural properties in the UK that get a 230/460V 100A supply. It's only offered if a single phase isn't enough, and the nearest supply is only 11kV single phase. Given that three phase overhead lines are normal, it isn't commonly used.

A 230/460V 100A supply is inferior to a 230/400V 100A three phase one. The former can supply 46kW, the latter supplies 69kW. The voltage being a little bit lower isn't that important.

A 230/400V supply is enough for pretty much all houses, offices and light industry. At 69kW for 100A, that supplies as much as most premises will need.

Answer 5

The split phase power is used in Canada and the USA but not in Europe. All electronics like computers, audio and video equipment may be powered with 110 V or 230 V AC. So split phase has no advantage over single phase.

All electric appliances used in apartments and residential homes may be used with a single phase only. Brushless motors for dishwashers and washing maschine may be built as induction motors with a capacitor.

Continuous water flow heaters for showering need much power, over 20 kW. The power distribution company may prefer to connect these as a symmetric three phase load.

Kitchen stoves may be connect to single phase as well as three phase. If used with one single phase circuit breaker, you may not use all cooktops together with maximum power.

Quick chargers for electric cars may require three phases too.

If you got solar panels with more power, a three phase inverter may be required by the provider.

So three phase power is better only for large loads to reduce neutral current and to balance load to all phases.

Answer 6

All the answers are very long, but this can be better shown with an exmple:

The North American 100A installation provides 240V * 100A = 24kW.

For an EU installation to provide 48kW, you need much less current: a typical 32A 3-phase installation delivers 400V * 32A * sqrt(3) = 22.2 kW.

For practical purposes, we can consider them equal in power.

Compare: three wires at 32A have significantly lower losses than two wires at 100A. Loss = current².