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In Reply to: RE: Confusion over the use of the word, "phase." posted by Al Sekela on October 29, 2009 at 15:37:51
...sometimes available is 360 degrees?
Or maybe in a 2-phase system, that is where 3-phase power is not available on the power company's distribution system, the phases are indeed 180 apart.
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Tin-eared audiofool and parttime landscape fotografer.
http://community.webshots.com/user/jeffreybehr
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Domestic power is simply single-phase. The use of the word, "phase," is inappropriate for domestic power when discussing the two hot legs. This is how the confusion arises.
Three-phase power does indeed have 120 degrees between the phases. The power company generates and distributes three-phase power, but domestic users are attached to only one of the phases. The transformers are the clue: they have a single core instead of a triple core.
...(the neighborhood is now 50 years old), and my domestic service has 3 lines plus neutral coming from that big transformer. The 2 physical halves of the breakerbox are fed by 2 of the 3 legs, while the 3rd (it's a 3-phase-delta system) runs to the AC system. As a result, my 2 120VAC legs are 120 degrees out of phase.
And I believe where 3-phase power is not available, the 2 120VAC legs that do arrive from the transformer are 180 degrees out of phase. Else how does one have 240VAC for one's waterheater and oven?
But maybe you'll tell me. :-)
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Tin-eared audiofool and parttime landscape fotografer.
http://community.webshots.com/user/jeffreybehr
3-phase-delta system
Arizona..... Had to be the only state that ran 3 phase power to a residential occupancy.Are you sure it is a delta and not a WYE? If it is a 3 phase 4 wire delta it will have what they call a "wild leg". From two hots to the neutral the voltage will be 120V nominal but from the other hot to the neutral it will be around 208V. And usually out on the utility pole you will see one big transformer and two smaller ones.
Sometimes only one big transformer and one small transformer. In this case it is called an "Open delta".At any rate if it is a delta the 120/240 is single phase fed from the bigger transformer and there is not a 120 degree phase angle.
A 3 phase 4 wire WYE transformer configuration has three equal voltage hot phases that have a 120 degree phase angle with respect to one another. Usually phase to phase is 208V nominal and from any of the three phases to neutral is 120V nominal. If the 3 transformers are mounted on a pole or platform, the transformers will be the same size. A 3 phase 4 wire WYE pad mount transformer will have all three coils inside one enclosure.
Jim
Edits: 11/04/09
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