"David Nebenzahl"

I'm posting this to try to settle an argument going on in another
newsgroup (alt.home.repair) 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:

http://www.3phasepower.org/2phasesystems.htm

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?


** It's clearly two phase power, no doubt about that.

There are two AC waves that differ only in phase and if both "phases" are
loaded equally, the neutral current is zero.

So it is completely analogous to three phase power.

The 90 degree system is just an obsolete odd ball only a moronic pedant
would even mention.



..... Phil