The disadvantage of the system is that, it requires a live
power in the main grid. If the grid fails during the working of
the system, the motor will speed up infinitely. So protective
measures must be taken to prevent this over speed, as it may
damage the motor. The phase sequence must also be correct
else the motor will run in the opposite direction. So measures
must be given for the motor so that it does not rotate in
opposite direction. Over current must also be prevented for
the protection of the motor.