, would anyone happen to know the term for the system by which electrical power is transmitted to a typical residence. It's 2-phase 3-wire; two "hot" wires 180 degrees out of phase, with the third being neutral or ground. Most outlets get ground and one phase for 115 v, with the 230-v outlets (clothes dryer, pool pump, etc)using both phases

I don't, but I'll bet somebody at your local utility company could tell you. Might wait till a weekday, when your chances are better that a real person will be there to talk to you.

Jackie: Thank you, but out of laziness I was hoping for a reply. Some members have extensive contact with such matters--no pun intended

"[S]ome people incorrectly describe split single phase services as "two phase", when in fact such services are really still single phase power." - wiki

-joe (go fly a kite) friday

tsu, thanks, just what I needed to know. Does one then not refer to the system as 115/230v split single phase

Here
http://www.reliance.com/mtr/pwrspy.htm
it says
Two phase power supply is found in only a few scattered areas around the U.S. and the world. Two phase motors are not generally available in stock; Check AC Products in Cleveland for availability. Two winding multi-speed motors are difficult to wind for two phases, therefore, transformation to allow three phase operation is recommended.

There is no special term mentioned for this system, nor for 3-phase supply. If you split a 2-phase supply, you would indeed get half the voltage.

ws: Thank you for that link, but as tsu points out, the 180-deg phase relationship of the two "lines" is not considered two-phase but only one. Aside from their relation to its frame, the split-phase motor doesn't even know its 230-v input is split

I suspect but cannot confirm that most all U.S. residences use this split-phase system

ws: Further thought suggests, as you indicate, that the 2-phase motor is rare, for I don't believe I've ever encountered one. Unlike the split-phase, however, wouldn't the 2 windings be "conscious" of neutral

Forgive the anthropomorphisms

Three-phase, however, are very common. Their claim to fame is that the direction of rotation can be reversed by reversing any two phases

Suggesting the question, wouldn't reversing the connection to a 2-phase motor also reverse it

You state that splitting a 2-phase supply would give you half the voltage. Now I've forgotten near everything I used to know about all that stuff, I agree that it would. However, if each phase were 115v, wouldn't the voltage across the two lines be 208 v instead of 230 v

Thank you again for your input, no pun intended

The two "phases" are 180° out of phase. Reversing the connection and it's still 180° out pf phase.



I bet I've forgotten more about this stuff than you have but I can't think of any reason why it shouldn't be 115 v. Doesn't even work out if you toss in sin(120°).

Fal, true, a split-phase motor won't reverse. Of course each line (or "phase") is 115v above ground, but it's not even "conscious" that its power source is any diferent from single-phase 230 v with neutral grounded. but if I understand tsu's refeence to the "two-phase" motor, with a phase difference of 120 deg the voltage between the two phases wouldn't be 230 v but 208 v (rms)

Other members should forgive us from getting so far afield