Final answer:
Keeping the start winding of a resistance split phase motor engaged too long can cause excessive heat due to high current, potentially leading to overheating and motor burnout. Typically, a centrifugal switch or relay automatically disconnects the start winding to prevent this issue.
Step-by-step explanation:
If the start winding of a resistance split phase motor is kept in the circuit too long, it could have detrimental effects. When the motor is first turned on, it usually draws a higher amount of current due to low back electromotive force (emf). As the motor reaches up to speed, the back emf increases and reduces the motor's current draw. The start winding is designed to help the motor start under load; however, it is not intended for continuous use and has less resistance, leading to higher current flows through it.
Therefore, if the start winding remains connected for too long, the motor will continue drawing a high current, which may cause excessive heat. This heat can lead to resistive power loss in the coils (P = I2R), potentially overheating the motor and causing insulation failure or motor burnout.
To prevent this scenario, most split phase motors include a centrifugal switch or a solid-state relay which automatically disconnects the start winding when the motor reaches about 75% to 80% of its rated speed, thus protecting the motor from excessive currents and overheating.