Coyne Electrical Trouble Shooting Manual, Educational Book Publishing Division, Coyne Electrical Radio School, 1948

This job is used to demonstrate the difference between the ends of each phase on a 3 phase winding, and to show that this difference must be taken into account when the phases are connected together.

Proper connection of the windings on any 3 phase motor, generator, or transformer, must be preceded by identification of the phase ends as starts and finishes, just as the proper connection of a battery to others must be preceded by the finding of the positive and negative terminals.

The simplest method of finding the starts and finishes of the phases in a three phase motor is given below. Follow each step carefully. With the windings connected star, a test will show unequal voltage per phase with an incorrect connection. This explains why the motor hums when the phases are improperly arranged.