[throwaway173738]

> Similarly the 240v version of this plug (6-15/6-20) has the same property: 15amp and 20amp versions. The 15 amp is two horizontal blades. The 20 amp is one horizontal + 1 vertical but swapped places compared to the 120v version. I do wish more builders installed the 240v receptacles in kitchens in the US. There is no technical reason we can't have higher power kettles and whatnot. If code required these in garages and kitchens more appliances would be available for them.

If we had more 240v circuits in garages and on the outside of the house you could use electric motors for more yard tasks. Batteries and gasoline is used often in the US because our branch circuits provide about half the power of a 240v branch circuit. You can buy electric mulchers that are powerful enough to grind tree limbs but they can’t run on a 120v circuits.

[Kaliboy]

How is 240v delivered in the states?

We get 3 phases to each home, phase to neutral is 127v, and that's the standard voltage, so loads are divided over the 3 phases.

230v we get through phase to phase connections. We also balance those for the 220v loads, but it's kinda risky due to the nature of our grid, being an island.

Whenever there's a fault they disconnect the zone affected but sometimes in the process we get VERY short but massive overvoltage events.

Since everybody generally uses 127v, as the system trips the 127v line voltage increases for a bit, often within spec but because we take 230v from between the phases it spikes to heights beyond spec and burns the devices.

[xenadu02]

We use a center-tap neutral except for commercial/industrial that receives three phase.

Most small-to-medium homes/businesses have two hot legs coming off each side of the transformer coil. The neutral is connected to the center of the coil and bonded to earth/ground so it becomes a 0v reference. Each hot leg to neutral is 120v. Between hot legs gives 240v. That neatly supports both voltages in a backwards-compatible way. Typically clothes dryers, hot water heaters, ovens/stoves, etc are 240v appliances. Lamps, USB chargers, and other small day-to-day stuff is 120v.

There are two failure modes that can happen but they are rare and usually only affect the customers attached to the affected transformer or a single customer.

1. Floating neutral. If the neutral becomes disconnected that causes floating voltages as the electricity backs up across the neutral and returns via the opposing hot leg. This presents as randomly fluctuating high/low voltages to 120v appliances but most 240v appliances don't use then neutral and don't care.

2. Damaged hot leg. One hot leg partially arcs to ground or is otherwise damaged. This causes half the 120v appliances to flicker/brown out. 240v appliances will see random low voltages.

Three phase is often delivered as wild leg/high leg delta so a neutral can be derived. It is usually setup so one phase (eg A/C) is center-tapped to make the neutral and two hot legs. This gives three phase power per normal and the same setup as a normal home would have: A/C forms two 120v legs wrt the center tap neutral. However you get 208v between the other phases and neutral so for high density housing you also need to balance the phases resulting in some apartments having 208v power rather than 240v. Thus most 240v appliances also support 208v here but unless you've lived in an apartment or worked on commercial/restaurant systems you'd never see that voltage.

Our breaker panels have 3-phase variants. You'd usually install both: a 240/120 panel for "normal" loads and a 3-phase panel for 3-phase and 240v split phase loads. Breaker design is the same: 3-pole takes up three slots and the bus bars alternate by 3 so every third point is on a different phase.