SOLUTION

• In a split-phase induction motor, the starting winding has a relatively small number of tums of fine wire.
• Consequently, its resistance is higher than that of the main winding.
• Owing to the fine wire used on the starting winding. the current density is high and the winding heats up quickly.
• If the starting period lasts for more than 5 seconds, the winding begins to smoke and may burn out unless the motor is protected by a built-in thermal relay.
• Therefore, the split-phase motor incorporates a means of disconnecting the start winding from the supply when the motor has reached sufficient speed.
• A typical method is with a centrifugal switch mechanism that opens a contact and disconnects the start winding from the supply when the motor is around 75 percent of its rated speed.