M Philbrook writes:
Show me the phase difference between your "TRUE" 2 phase and the
"FALSE" 2 phase that you seem to know so much about.

Ah, this old argument... I put some graphs at [1] that show the
differences using non-sine waveforms.

Stepper motors use 2 phase power. The zero crossings occur at different
points in time to give the motor a "rotating" power profile.

Houses use single phase power with a central tap. It's no different
than having a power transformer for your project that provided 5, 15,
and 24 VAC via different taps. A house transformer provides 120 and 240
VAC via taps. We typically tie the central 120vac tap to neutral,
providing -120 and +120 taps instead. This is no different than tying
your project's 5v tap to "ground", providing -5, +10, and +19 vac taps.

One way to "prove" the difference: look for upstream noise on the power
line. With two phase power, the other power line should have the same
noise 90 degrees later (or not at all). In single phase power, the
other power line has the same noise but negated.

I.e. houses have two 120VAC taps which differ in magnitude (or polarity,
+120 vs -120), not phase. Like batteries, you can use one tap for 120v
or use both in series to get 240v.

Another way is to look at my driveway, which only has one power line
coming from the road (plus a ground) (I have my own transformer). If I
had two phase power, I'd need at least two (originally 2 phase used
four, which is why three phase won out - fewer wires) power lines.

[1] http://www.delorie.com/electronics/s...two-phase.html

https://en.wikipedia.org/wiki/Single...electric_power
https://en.wikipedia.org/wiki/Two-phase_electric_power
https://en.wikipedia.org/wiki/Three-...electric_power