Nowadays with devices with switching mode power a lot of appliances even sold in the US can accept voltages in the range of 100-240V, and typically these power supplies are more efficient if they are run at 240V. Why in new installations in the US homes don't you put 240V outlet everywhere? For me it would make sense to do that, for example if you have to plug in a computer, or TV, or practically everything modern.

Basically it's inertia. How would people handle using all the existing 120V devices with 240V outlets?

Most Americans don't know this, but there already are exiting NEMA 240V outlets in use in the US. There's, of course, the commonly-known "dryer outlet" and "stove outlet" (which are each unique to that application), but there's also some standardized ones for lower currents than those. Sometimes you'll see them in (older) houses that have very large window-unit air conditioners, because 120V isn't sufficient to run an A/C over a certain BTU rating. IIRC, these outlets look similar to regular 120V outlets except one of the prongs is sideways.

You're absolutely right that most electronics these days can run dual-voltage; they do this because it's very easy to do with modern switching power supplies, and lets you engineer and sell one product worldwide instead of making different versions for different markets, and all you have to do is include a different power cord. However, changing the infrastructure is a totally different proposition. Lots of things don't work on 240V: think about toasters, refrigerators, lights, etc. I even have a German-made electric toothbrush which only runs on 120V (presumably, it uses a simple transformer in the charger base, which is inductively coupled to the toothbrush; the charger base is only rated for 120V, since transformers have to be tapped for the appropriate voltage).

Basically, it would be cool if the entire country switched over to 240V outlets everywhere, as it would give us superior toasters, vacuum cleaners, etc., but there'd be huge confusion for a long time, probably some fires, and the benefit generally isn't worth the cost.

I'll also add that switching to 240V would give us lower line losses everywhere on the grid (saving energy). Just think of all the power wasted in house wiring multiplied by millions of households. For an illustration, get out your vacuum cleaner, and vacuum your house. Now that it's been running for a while, grab the power cord: it's rather warm, isn't it? The power also went through your wiring in your walls, through your panel, and up to the transformer for your house, at that voltage. (Even worse, since the US has 120V split-phase power, it was probably unbalanced, leading to even greater line losses.) Doubling the voltage to your vacuum cleaner would mean you'd only waste 1/4 as much energy in the form of heat due to wiring losses, assuming the vacuum has the same-sized motor.

Of course, suddenly switching everyone to 240V would also mean millions of vacuum cleaners and toasters going into the landfill, so that wouldn't exactly be environmentally-friendly either.

In the US, 240V is conflated with high amp circuits, and danger.

You would need at least a different plug and socket for this, but there are probably still a good number of appliances that are tied to the service voltage, so you would need to run separate circuits or point of use transformers for those. That's confusing and expensive.

That's an interesting point about using a different plug and socket. Perhaps this would be a good time to deploy IEC 60083 Type G plugs, which were carefully designed for safety at higher voltages? They already see some use, so there is an existing supply chain for plugs, sockets, adapters, etc.

If the US did start adding 240v circuits they would almost certainly use NEMA 6-15 or 6-20 plugs for compatibility with (the rare) 240v appliances like air conditioners or hotplates which use those plugs today.

Appliances which use universal power supplies tend to be low power. The highest-power device with a universal PSU that I can think of that the "average" person would have would be a computer, but even high-end gaming computers tend to top out around 500 Watts when running full-bore. Even large TVs don't usually draw more than 100 Watts at most. The rest of the devices with universal power supplies tend to be things like phone chargers which draw almost no power. None of these devices draw enough energy for the increased efficiency to matter. Devices where it would matter tend to have large motors or heaters that run directly off line voltage.

To my knowledge gaming computers are normally more in the 500W-1200W range, though granted you rarely max out the 1200W. I used to sit north of 500W with my relatively modest build a few years back ([email protected] and only one GPU).

American 240V outlets are two-phase (two hot plus neutral). A European 240V appliance (which is one hot plus neutral) cannot safely be plugged in to such an outlet.

European plugs aren't aware of any hot/neutral polarity and devices are not built to treat a neutral phase differently from a hot phase. A separate grounding wire is used for safety.

I'm assuming most European appliances use double-pole switches?

United States 240V is single phase. 120V is split phase, with the neutral drawn from the middle of the coil.

You're right, I was confusing that with true multi-phase power.

>American 240V outlets are two-phase (two hot plus neutral).

No, that's single-phase. The "phase" is measured across the hot wires; the wire itself isn't the phase. There's no such thing as "two-phase".

Yeah, I got confused because some people lazily refer to split phase as "two phase". Apparently I need a refresher session with my textbooks. :(

Actually there is janky 90 degrees out of phase two phase power. Who knows if there's anywhere still using it but it was a thing.

It is somewhat common to make some of the wall outlets in the kitchen 240V sockets, but definitely not common to equip all the outlets in the house that way.

Because any appliance that isn't build for 240V would break, if not hurt/kill you when powered with twice the voltage it was designed for.

Well presumably, they'd change the outlets to 240V-specific outlets. We already have NEMA outlets for 240V single-phase applications, even in residential buildings.

Of course, then you'll have the problem where someone moves into a new house and then they can't use any of their stuff because it doesn't fit into the outlet. Then they'll go to Home Depot and buy an adapter, which just converts the physical outlets (and has a big warning about not using for devices not rated for 240V), and use that with their heater or toaster or vacuum cleaner, and start a fire that burns down an entire apartment complex.

As well the long trend in the US is for devices outside the kitchen to use less power. Whens the last time you overloaded a breaker in a bed room?

I used to do it all the time, just by running my laser printer. I was in an old house that some amateur must have wired, so all the power for the entire second floor, plus both bathrooms, plus all the lights on that floor, were routed through a single GFCI outlet. It would pop every time I ran the laser printer, but only the first time. After I reset the breaker (in the dark, because the lights would go out), I could try printing again and it wouldn't pop that time.