On Feb 19, 3:53*am, Nick Mueller wrote:
...
Singel phase 120V, two phase 240V.
...
Nick

You could logically call it two phase since they are 180 degrees
apart, but the term is used instead for Tesla's original system of 90
degree phase shift. He was given the challenge of reducing brush wear
on DC motors and had the inspiration that a sine plus a cosine at
right angles gives a smoothly rotating vector, in other words a
rotating magnetic field to pull the armature around with no brushes
needed.

Modern single phase motors create a temporary second shifted phase
that they need to start turning with an extra start winding with
series resistance or capacitance to delay the current. The click you
hear when the motor starts or stops is a centrifugal switch in series
with the start winding.

Jim Wilkins