AC Motors AC MOTOR THEORY For purpose of explanation, rotation of the magnetic field is developed in Figure 2 by "stopping" the field at six selected positions, or instances.   These instances are marked off at 60° intervals on  the  sine  waves  representing  the  current  flowing  in  the  three  phases,  A,  B,  and  C.   For  the following discussion, when the current flow in a phase is positive, the magnetic field will develop a north pole at the poles labeled A, B, and C.  When the current flow in a phase is negative, the magnetic field will develop a north pole at the poles labeled A’, B’, and C’. Figure 2    Rotating Magnetic Field Rev. 0 Page 3 ES-12