[Al_The_Man]

On the subject of motors and phases mentioned in this thread no one ever seems to mention that on a single phase system both phases are 180 degrees apart due to transformer coupling at the pole (residential) and not the 120 degrees I think many are assuming and might lead to some confusion. I was told this, researched it and verified this many years ago by doing a phase measurement with o-scope on the home ac line. (measured in my home but that could be different elsewhere.) On a true three phase system you'll have that 120 degrees of separation between phases.

On a rotary phase converter you start with two phases 180 degrees apart (from residential power) and produce the third phase close to the others by adjusting the power factor with capacitance.

Actually a RPC uses single phase to produce three phase.
There is 180 degree difference with respect to centre tap or Neutral, which is still single phase (with a centre tap).
Not to be confused with two phases. There is no 180° difference between the 240v, because it is 1 phase.
Also neutral is not involved with WRT to a RPC.
Think of a motor fed by single phase as an auto transformer, which it is actually what it is, the three phases 120° apart will be produced, without the introduction of capacitors, capacitors are used to improve the power factor.
There were some good articles published in the late 90's, this is one link
http://www.metalwebnews.com/howto/ph-conv/ph-conv.html
Also the Metalworking.com drop box 1998 files FRW- et al.
show the wave forms in detail.
Al.