This is the question: Is the 120/240 volt system supplying American homes single phase or two phase? I have also heard the term "split phase" to describe it. Basically, a transformer just before your house's electrical service creates two 120 volt ac sources in series, using a center-tapped secondary. The middle leg is grounded at the "telephone" pole and at your house's service entrance. I consider it all single phase due to the following consideration: Yes, the two high legs are 120 degrees out of phase with respect to one another and one might consider this as two phases. But whether you run a motor off 120 volts or 240 volts, it is still a single phase motor. A two phase motor is used for servos.