M
MAGNETIC POLARITY
It is a fundamental principle of a winding that adjacent poles must be wound to give opposite magnetic polarity. This does not mean that the coils actually have to be wound in this direction before being placed into the stator. It does mean that the winding must be connected so that, if the current proceeds through one pole in a clockwise direction, it must proceed through the next pole in a counterclockwise direction. This principle is used to determine the correctness of connection diagrams.
MEDIUM MOTORS
Motors in NEMA 143T to 449T frames.
MEGGER TEST
A measure of an insulation system’s resistance. This is usually measured in megohms and tested by passing a high voltage at low current through the motor windings and measuring the resistance of the various insulation systems.
MOTOR
A device that takes electrical energy and converts it into mechanical energy to turn a shaft.
MULTI-SPEED MOTORS
A motor wound in such a way that varying connections at the starter can change the speed to a predetermined speed. The most common multi-speed motor is a two speed although three- and four-speeds are sometimes available. Multi-speed motors can be wound with two sets of windings or one winding. They are also available either constant torque, variable torque or constant horsepower.