What happens if one winding of the 3 phase motor polarity changes?

For correct rotation, the phase sequence has to be correct (L1 to M1, L2 to M2, and L3 to M3 - where L refers to LINE and M to MOTOR phase).

If two phases are connected incorrectly (L1 to M2 and L2 to M1, for example) - the motor will rotate opposite to the desired direction. NOTE: THIS IS NOT THE SAME AS CHANGING THE POLARITY OF A SINGLE PHASE.

If one phase has the polarity changed, then the magnetic field distribution within the motor winding becomes uneven, and the output torque will "pulse". (To see this for yourself - plot the three phases and their sum on a single graph. Then switch the polarity on one phase and see the difference in the waveforms.)


This may or may not cause irrevocable damage to the motor and driven equipment - it depends on how much mechanical margin is built into the installation. It certainly is not a "good" condition, though - the chance of a failure is significantly increased.

The windings of 3-phase motor are not in same direction. For example 3 phase 60Hz 1770 RPM motor, so 4-poles in three phase a total 12 groups of magnetic wire coil. So 6 groups magnetic wire coil in clock wise and 6 groups magnetic wire coil in counter-clock wise direction alternatively. Each terminal 4 groups of coil (2 groups clock wise/south pole direction and 2 poles counterclock wires/north pole direction) connected alternatively in other terminal 2 and terminal 3 group of coil to make the rotor to rotate. If one magnetic wire coil by mistake change wound rotation/direction, per GoHz experience, the rotor will not rotate and seems like overload and the stator winding will burn because 5 group of magnetic wire in south pole direction and 7 group of magnetic wire in north pole direction the magnetic field is not balance.

Three phase motors on a three phase three wire system only need two line and motor leads interchanged to reverse the motor rotation. A polarity change of one phase in relation to the other two in a typical three phase generator feed system that is functioning properly is impossible.