Electrical

I guess it's big on electrical questions this week. What are phases? I saw an item listed as 220 single phase. I guess that would mean there are more phases and what's the max for common household current?

Two Hots is single Phase 3 hots is 3 Phase Hey! I don't make the rules,
Single is all one needs for the home unless you have some large electric motors that are 3 phase which I doubt very much or you would know the answer to this.
Walt

Thanks, never run into it.

3 phase is generally industrial.

All AC power generated in the US is three-phase. Single phase power is just one leg of three phase.

Polyphase power was invented by Nicola Tesla, and made large-scale AC power generation practical. Although it is possible to have more than three phases, there's no practical reason to do so. The advantage of three phase over single phase is that it provides much more constant power, so big generators and motors don't vibrate themselves to pieces. With single phase power, instantaneous power changes at 120 cycles per second. In a three phase device, each phase is 120 degrees out of phase with the other two; this overlapping means that power is nearly constant and almost eliminates vibration.

The two phases, or legs, in a single phase 240 circuit are 180 degrees out of phase with each other, but we still call it "single phase".

If you look at any AC transmission line, you will almost always see three conductors: Three phases and a neutral. (Sometimes you'll see five conductors because there's two neutrals.) If you see a transmission line with only two conductors, it is probably DC.

There are actually two configurations for three phase: "wye" (or "Y") and "delta". A wye-wound motor has one end of each winding tied to a common neutral. A delta motor has no neutral, each end of each winding is connected to the other two windings.

If you want to see what a three phase generator looks like, just take apart your car's alternator.

I think you better think about your statement about 2 lines being DC. There are millions of miles of two lines AC power around the good old USA.

Hi Gene,

You're right that there are plenty of single phase power lines, if you're talking about the last few miles up to the consumer. But I wouldn't call those transmission lines. I think they are generally referred to as "distribution lines". A matter of semantics, to be sure.

Single phase power also when using two out of three phases of a three phase supply.
We use a lot of 600V single phase to 120/240V transformers here in small offices attached to industrial complexes.