Why is 220V called single phase when it has two phases?

[markba633csi]

Building power supplies with center tapped secondaries you get acquainted with this idea early on- it's the same thing in miniature
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[GoceKU]

Maybe you've read an european thread, here in europe 220v is single phase, 380v is 3 phase, just a tought.

 

[fast freddie]

Maybe this will help.

The power going to most residential service (In the US), is 1 leg of the three phase high voltage. That 1 leg, is then lowered by transformers into 2 120 volt, legs, and a neutral. If you look close at the transformer, it has 1 hot going in, and 2 half voltage hots coming out, and a ground in and out.

Here is a good page that explains it.



http://waterheatertimer.org/See-inside-main-breaker-box.html

There is such a monster as 2 phase, in some parts of Philadelphia, and a few other rural areas in the US. So you can run across 2 phase motors once in awhile.

Maybe this will help.

The power going to most residential service (In the US), is 1 leg of the three phase high voltage. That 1 leg, is then lowered by transformers into 2 120 volt, legs, and a neutral. If you look close at the transformer, it has 1 hot going in, and 2 half voltage hots coming out, and a ground in and out.

Here is a good page that explains it.



http://waterheatertimer.org/See-inside-main-breaker-box.html

There is such a monster as 2 phase, in some parts of Philadelphia, and a few other rural areas in the US. So you can run across 2 phase motors once in awhile.

Superburban is dead on right, single phase 220 is coming from one wire off the powerline

 

[British Steel]

The center tapped transformer is stupid and they should have just done 220V without the neutral, but we're stuck with it now. There was probably a good reason back in the day with insulation requirements and such. From the power companies' perspective, it's one phase of a 3 phase feed, so single phase. The center tapped neutral L1/L2 creating opposed waveforms doesn't matter to them.

Even better would be 3 phase 480V standard, but that's pushing it.

Most (nearly all) of the rest of the developed world has 415 3 phase, centre of the Y winding earthed and used as neutral, so we get 240v phase to neutral - although harmonising with Europe has resulted in "nominal" 230 / 400 service, but the harmonisation allows +/- 10% so we keep our 240 / 415 v

Dave H. (the other one)