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Comment by dnm | Hacker News Reader

> the voltage in those two power-carrying wires is constantly switching directions

I'm not buying this (in the USA). I've been in my breaker box. For a typical 110 volt outlet, the black (hot) wire is connected to the breaker, which is connected to one of the wires coming into the house from the street. The white (neutral) wire is connected to the same ground bracket that the bare (ground) wire is connected to.

240 volt connections (like my dryer and range) are taking a hot line from one of the lines coming into the house and another hot line from the other line coming into the house. You can see it on the bus bars in the breaker box. That's why dual breakers are used. Adjacent breakers pull for different bus bars.

*edit typo

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Right, that is correct. To understand how that works, you have to realize that there is no such thing as an "absolute voltage", only the voltage difference between two wires.

In a breaker box, one wire (white) gets tied to ground, and the other wire (black or red) goes between +170 (relative to ground) and -170 (relative to ground). The black and red wires are 180 degrees out of phase, so when the black wire is at +170, the red wire is at -170. This gives a 340V peak difference between the black and red wires, which averages to 240V. You get your normal 120V outlet power between the hot legs and ground/neutral, and you get your 240V dryer & water heater power between the two hot legs themselves.

So, in a normal outlet, we can safely say that one wire is "more positive" than another, and that this flip-flops through time. When we look at voltages relative to ground, though, one wire stays put at 0V while the other goes between +170 and -170. It's just a question of where you put your reference frame.

This is not what you said in the other post. You are confusing people, and you should edit it.

There are two phase wires and one neutral. Diff between phases is 240V, the diff between any phase and neutral is 120V.

In Europe, you have three phases (R,S,T) and neutral. Here the diff between any phase and neutral is 250V, and the diff between any two phases is 380V.

In Europe, you have three phases (R,S,T) and neutral.

Is that everywhere, to every building?

In the USA, of necessity, power generation is three phase, large scale power distribution is three phase. What's confusing is that the previous discussion didn't differentiate between residential and commercial.

In USA residential areas nobody gets all three phases to their house or apartment. As discussed in previous comments, a house gets two hot wires and a neutral. In fact, to save money, sometimes entire neighborhoods only get one or two phases[1]: "spur lines" branching off the main line to provide power to side streets often carry only one or two phase wires, plus the neutral

In commercial and industrial settings it's common and necessary to deliver all three phases to the building. E.g. large electric motors require all three phases.

[1] https://en.wikipedia.org/wiki/Utility_pole#Power_distributio...

Unless you are in a really remote place you have three phases. Yes. Our stoves are typically connected to it (obviously not to all phases at once).

The explanation in that paragraph is not necessarily incorrect, just confusing because it talks about voltage "in" wires and isn't clear about what two terminals are being referenced.

It is true that the voltage between live and neutral changes sign, so neutral is sometimes 170V above live. But neutral is almost always at ground, and live goes to -170V relative to ground.

That last paragraph though seems wrong, so OP may have been confused himself when writing.

Ground is literally the ground. The Earth makes a good return path. The hot wire is going positive and negative relative to the land you stand on.

This isn't true in your home. The neutral is bonded to ground at a single point, in the main panel of your house. Current essentially all returns on the neutral to secondary of the pole xformer. The Earth is much higher impedance than the path back to the pole. Even during a ground fault event the current returns on the ground (technically EGC) to the bond point in the panel, and then from there back to the secondary of the utility pole.

Grounding to earth itself mainly serves to hold the potential of your house near that of the pole.

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