Two phases or not?

David Nebenzahl · 2011-01-22T02:09:26+00:00

I'm posting this to try to settle an argument going on in another newsgroup ( about phases in electrical power.Over there, someone posted a question about GFCI breakers that morphed into a discussion of multiphase electrical power. A disagreement arose thereafter about whether a center-tapped transformer actually delivers two separate phases of electricity or not. I'd like to get opinions here, since at least some folks here have engineering backgrounds: over there (a.h.r.), not so much. People there tend to be more electrician types, rather than EEs and such.The discussion started with a mention of 2-phase power. Turns out that in the world of electrical power, this has a specific meaning. It refers to a now-obsolete system of generating power in 2 phases that were 90° apart, and was used at Niagara Falls:And of course there's 3-phase power, widely used today.The problem is this: several people, myself included, contend that the two "legs" of power produced by a center-tapped transformer do, in fact, constitute two separate phases of power, 180° apart. (This is how household power is delivered in North America, with a step-down xfmr at the power pole delivering 240 volts in the form of 120-0-120.)Now it's true that in the electrical industry, this is called "split-phase" power, and if you tried to tell the guy behind the counter at the electrical supply house that it's 2-phase, he'd look at you funny.However, I (and others) say that this is, in fact, true 2-phase power, even if it's not called that. It just happens to be trivially easy to generate it from a single phase, as it only involves inversion. (Unlike 3-phase, which requires rotary converters or electronic devices to generate from single-phase power.)Take, for example, any push-pull amplifier with a phase inverter or phase splitter in front of it: it generates two separate phases out of a single phase.So, what do y'all say?-- Comment on quaint Usenet customs, from Usenet: To me, the *plonk...* reminds...