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Typical residential service in the US is 240v single phase. The transformer on the pole is putting out 240v, but there's a center tap on the transformer that's

Typical residential service in the US is 240v single phase. The transformer on the pole is putting out 240v, but there's a center tap on the transformer that's bonded to ground. That's your neutral. The other two legs are essentially +120v and -120v relative to ground/neutral. Your dryer hooks up to both legs and sees the full 240v. Don't ask me how grounding works for 240v appliances. I have no idea. I am not an electrician or EE. I just spent a bunch of time looking into this when I got my 240v table saw and had to hook it up to something. As proof that I'm not totally bullshitting you: until recently our house had a 120v outlet on a 240v breaker for a baseboard radiator. The electrician was here to fix an unrelated issue, and rejiggered things in the panel to hook it up to a 120v breaker. As far as I understand it (not very) there is no such thing as two-phase power.

JdeBP 6y ago
Enjoy https://youtu.be/jMmUoZh3Hq4 https://youtu.be/jMmUoZh3Hq4 .
nickff 6y ago
The 240V that you're talking about is what I mentioned as 'mirroring'. There definitely is such a thing as two-phase power, my electric car charger is 208V from two industrial phases, and our reflow oven is 208V, from two similar phases.
- labcomputer 6y ago
  That's two phases of a three-phase supply. From your car's or oven's perspective, it's still just single-phase power that happens to be floating w.r.t. ground.
  - nickff 6y ago
    Well, it would be the same as single-phase power (to the device) if the devices were not connected to the neutral. The oven actually takes one of the phases (along with the neutral), and uses it to power some accessories.
    - mauvehaus 6y ago
      With the massive caveat that I don't have a first principles understanding of any of this: I don't thing any individual load in your oven takes both legs and the neutral to do work. They're all either 120v or 208v single phase. Aside: a lot of motors can run on either 240v single phase or 208v single phase (or, presumably, anything in between?). Take a look at Grainger or McMaster-Carr.
- MisterTea 6y ago
  That's still single phase as the power you're seeing is the vector sum of the two phases.
toast0 6y ago
> Don't ask me how grounding works for 240v appliances. I have no idea. Ground is 'the same' for 240v and 120v on split phase. A usually bare copper wire is run from the ground pin to the service panel, in the main service panel ground and neutral are connected together and to the utility neutral and the grounding rod. Most 240v outlets are hot-hot-ground, or hot-hot-neutral-ground; some older outlets were hot-hot-neutral and the appliance was supposed to be wired separately to ground (and we can all suppose how often that was done properly, resulting in that outlet type becoming disfavored). I'm currently rejiggering a 240v wired box for 120v outlets, after finding the wires in the panel and confirming they don't power any other 240v outlets, I'm connecting the white wire to the neutral bus bar, and the black wire to a spare 120v breaker, and then it's normal wiring of the outlet.
MisterTea 6y ago
> As far as I understand it (not very) there is no such thing as two-phase power. Because it's obsolete (but still exists in some places like center city PA). Two phase has two windings in the generator 90 degrees apart. Service was delivered via 3, 4, or 5 wires. Three phase beat it for a number of technical and economical reasons.

JdeBP 6y ago

Enjoy https://youtu.be/jMmUoZh3Hq4 https://youtu.be/jMmUoZh3Hq4 .

nickff 6y ago

The 240V that you're talking about is what I mentioned as 'mirroring'. There definitely is such a thing as two-phase power, my electric car charger is 208V from two industrial phases, and our reflow oven is 208V, from two similar phases.

labcomputer 6y ago
That's two phases of a three-phase supply. From your car's or oven's perspective, it's still just single-phase power that happens to be floating w.r.t. ground.
- nickff 6y ago
  Well, it would be the same as single-phase power (to the device) if the devices were not connected to the neutral. The oven actually takes one of the phases (along with the neutral), and uses it to power some accessories.
  - mauvehaus 6y ago
    With the massive caveat that I don't have a first principles understanding of any of this: I don't thing any individual load in your oven takes both legs and the neutral to do work. They're all either 120v or 208v single phase. Aside: a lot of motors can run on either 240v single phase or 208v single phase (or, presumably, anything in between?). Take a look at Grainger or McMaster-Carr.
MisterTea 6y ago
That's still single phase as the power you're seeing is the vector sum of the two phases.

toast0 6y ago

> Don't ask me how grounding works for 240v appliances. I have no idea. Ground is 'the same' for 240v and 120v on split phase. A usually bare copper wire is run from the ground pin to the service panel, in the main service panel ground and neutral are connected together and to the utility neutral and the grounding rod. Most 240v outlets are hot-hot-ground, or hot-hot-neutral-ground; some older outlets were hot-hot-neutral and the appliance was supposed to be wired separately to ground (and we can all suppose how often that was done properly, resulting in that outlet type becoming disfavored). I'm currently rejiggering a 240v wired box for 120v outlets, after finding the wires in the panel and confirming they don't power any other 240v outlets, I'm connecting the white wire to the neutral bus bar, and the black wire to a spare 120v breaker, and then it's normal wiring of the outlet.

MisterTea 6y ago

> As far as I understand it (not very) there is no such thing as two-phase power. Because it's obsolete (but still exists in some places like center city PA). Two phase has two windings in the generator 90 degrees apart. Service was delivered via 3, 4, or 5 wires. Three phase beat it for a number of technical and economical reasons.