Japan is just 100V, not 110/115/120, there are some appliances that will use 200V. Similar to how the US has 240V. The weird bit with Japan uses both 50 and 60hz.
Right. That was the thing. They're 50/60hz based on location. I know something was different but I misremembered.
For the US, they use 240v split phase. The secondary on the transformers have a middle tap, called neutral, so if you go from line to line, you get 240v, if you go from either line to neutral, you get 115/120v approximately. The benefit to it is that you can use two 120v devices in series, one connected to line 1, the other on line 2 and the neutral connections simply connected together. Total load voltage is 240v.
But appliances that use a lot of current like clothes dryers, air conditioners/heat pumps, water heaters, and ovens, can be connected to 240v directly.
It creates some interesting opportunities and challenges.
People get this wrong all the time. North America is 120V for the usual outlets, but what comes into your house is 240V split phase. You get 240V in places you want 240V, like electric stoves or clothes dryers.
Exception is apartments, especially those with elevators, which use three phase. Then you combine two legs to get 208V and your electric stove is kinda shitty.