Some time, the rotor of a squirrel cage induction motor refuse to start at all particularly if the supply voltage is low this happens especially when number of rotor teeth is equal to number of stator teeth, because of magnetic lacking between the stator teeth and the rotor teeth. When the rotor teeth and starter teeth each other, the reluctance of the magnetic path is minimum, that is why the rotor tends to remain fixed. This phenomenon is called caging or magnetic locking of induction motor.