Media for Re: 208/240V, was: 25 Hz Powe

Re: 208/240V, was: 25 Hz Powe

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I think the confusion comes from the use of ground as a reference: a wye-connected three-phase circuit has three distinct phase angles ** with respect to ground **. In a center-tapped secondary delivering

240/120 to a home, there is only one phase angle with respect to ground. The polarity is different, of course, but the absolute value of the angle is the same.

The disparity might also be an accomodaction to history: some electrical systems used to deliver two phases of power separated by 90 degrees (and thus requiring four wires). See

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and

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for discussions.

If I had to guess, I'd say that electrical engineers decided to call our usual 240/120 CT arrangement "Single phase" to distinguigh it from the four-wire two phase systems, and possibly because engineers think in terms of differences: two wires only have one angular difference.

If there is a "Two phase" system in current use (pun intended), I think it would be a delta-connected service with one leg grounded. I don't know what an electrician would call it, but "Delta breakers" are commonly used for this arrangement, i.e., there are panels with two-pole breakers that control two legs of a delta feed, with the third being grounded. Come to think of it, maybe this is the "standard" for delta: any electricians care to comment?

HTH.

William Warren (Filter noise from my address for direct replies)