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Comment by bluGill | Hacker News Reader

3 phase is very common in the US. Most single family houses don't have it, everything else is likely to have it.

For chargers 3 phase gains nothing. For induction motors 3 phase is useful - but in the modern world even where you have 3 phase you often will run the power through a VFC just so you get control of RPM. For a few other things 3 phase is nice because there is always one phase that isn't near zero to draw power from, but where that matters you can work around it with a few capacitors.

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Theoretically perhaps, but practically, most single phase AC EV chargers on Europe/Australia etc. are only 7 kW but 3-phase are 11 or 22 kW (both 7 kW and 22 kW are about 30 A per phase, but three phase you obviously have three of them, so three times the power!). That’s not “gaining nothing”!

While sometimes you get more power on 3 phase, that is only about the size of the feed and nothing to do with 3 phase.

But you have three feeds giving you three phases to use, so 3x the power available to you. Out here, even electric stoves (with ovens) have 3 phase connection options and tankless water heaters almost exclusively come as 3 phase models.

Power is volts times amps. 3 phase just means you add the power of all three phases, but you can get the same power from one phase with a little algebra. You need different size wires and breakers, but there is nothing there that 3 phases gives you.

Let's say you have a cable with 2.5mm^2 wires, each of which can carry 20A of current to stay within code. At 230V that's 4600W.

Now you want more power, to keep the math simple, let's say 13800W (3x the power above).

With a one phase system, for 3x the power, you need 3x the size of wire, so 7.5mm^2, ie. 3x the amount of copper (since all wires, neutral and PE have to be that size too).

With a three phase system, you can get the same power with 3x2.5mm^2 live wires (+1 neutral + 1 PE), so instead of 3x the amount of copper, you only need 5/3's of copper to get 3x the power.

Not sure what PE is in this example, but you don't need a neutral in 3 phase.

You don't need it in a "triangle"/"delta" wiring, but you need it in a "star"/"Y" - https://www.electronicshub.org/comparison-star-delta-connect...

PE is protective earth, grounding wire. Usually you need PE and neutral lines separate for FID (GFCI) protection.

You’re again talking in hypotheticals and ignoring the practical factors.

Around here, it’s usual for the utilities to limit residential services to 80A per phase (commercial properties can get a lot more).

So for a residential property you can literally get three times as much power by upgrading from single phase (which is common for small houses) to three phase (less common around here but available) due to this limit.

In theory I could just get a single phase service of three times the current, but in the real world the utility won’t give me that and makes me upgrade to three-phase.

This is by policy, since it helps balance the phases in the grid back to the local transformer, which the utility wants, so they also limit, for example, how much solar export you can do per phase for residential property - theoretically I should be able to export 15 kW on a single phase, but they don’t let me, so in the real world I am limited to 5 kW per phase, meaning I can only export 5 kW on single phase or 15 kW on three phase.

So in terms of pure electrical theory you are correct, but when thinking about real world policies of electrical utilities due to how power grids are designed, you do get a lot of benefit from three-phase.

P=sqrt(3) IV cos Theta not just three times IV

With three phases in Europe you get 400v, which means less amps for the same power, which means lower losses or thinner cables?

You can get 400V 3 phase in the US. While houses don't, almost all commercial locations have it already. So most public chargers in the US have 3 phase available. charge at home doesn't, but those tend to be lower power charge all night vs the charge in half and hour commercial chargers.

The NACS standard still only supports single phase power. It was the electrician who installed my home charger that said it is why they weren't in Europe homes.

NACS supports either one or two phases for AC charging which would be used in most home chargers. A really high power charger would use DC with the AC/DC conversion happening before (and that could be from a three-phase source)

What the US has is split phase power, when one phase is 240V and that is split to make two 120V legs. NACS supports single phase power, either 120V (Level 1) or 240V (Level 2).

There is no such thing as two-phase power, there is single-phase or three-phase. Since three-phase is better than two-phase.

You can look at it either way. "Phase" literally means the offset of the waveforms. With 3-phase, each of the phases is 120° out of sync. With split phase, you can look at it as a single, 240V phase with neutral in the middle, allowing it to be split into two 120V halves. Or you could look at it as two 120V phases, 180° out of sync, such that the difference between them is therefore 240V.

> NACS supports either one or two phases for AC charging which would be used in most home chargers.

Lots of european homes have 3-phase service. I have 3-phase 400V in my flat.

3 phases give you 3x the power for only 2x the amount of copper

And two phases give you 2x the power for the same copper.

3 phase typically has 400V between the phases and neutral in Europe, the phases don't gain you anything, but the voltage does.

Pretty sure residential 3-phase in Europe is 400V phase-to-phase, it's 220V phase-to-neutral.

make that 230V (min.) or rather 240V (nominal).

230V nominal in EU

You're right, though tolerances allow for up 253V since 2009. I usually measure between 235V and 242V from the wall.

It's 220/240 volt RMS to neutral, which is about 312 volt maximum to neutral at the top of the phase.

Voltage is solely a matter of how the transformer is wound. In the US you get a choice when you contact the power company, 208, 240, 440, and 480 are all voltages I've personally seen in the US, depending on the area (not all utilities will provide all voltages, so there are some I haven't seen)

3 phases give you three times amount the power as 1-phase with only 4 wires (instead of 2 in a single phase, or 3x the thickness).

I'm guessing the calculation would be based the other way, i.e. whether there is an installed base or not. If you have a 3-phase source, not using all the phases would limit total power delivery needlessly. So most European residences will want 3-phase charging.

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