What Is The Difference Between Starting And Running Capacitor

When it comes to understanding the inner workings of electric motors, capacitors play a crucial role in ensuring efficient operation. In particular, both starting and running capacitors are essential components that serve distinct purposes in the motor’s operation.

Starting Capacitor

Starting capacitors, also known as start capacitors, are specifically designed to provide the extra torque needed to start a motor. They are generally used in single-phase electric motors to help overcome the motor’s inertia during startup. The starting capacitor is typically only in use for a short period, allowing the motor to reach its full operating speed. Once the motor has reached its operational speed, the starting capacitor is taken out of the circuit by a switch or a relay.

Running Capacitor

On the other hand, running capacitors, or run capacitors, are designed to help maintain the motor’s operational efficiency once it has started. These capacitors are continuously connected to the motor’s winding, providing a phase shift in the motor’s electric current to optimize its performance. While the starting capacitor provides the initial push to get the motor started, the running capacitor ensures smooth and efficient operation throughout the motor’s running cycle.

Differences and Applications

The primary difference between starting and running capacitors lies in their respective purposes and usage. Starting capacitors are used to provide the initial boost to overcome inertia and help the motor reach its operational speed, while running capacitors are essential for maintaining the motor’s performance and power factor during operation. It’s important to note that using the correct type of capacitor for the specific motor application is crucial for optimal performance and longevity of the motor.

Additionally, the capacitance values for starting and running capacitors differ based on their intended use. Starting capacitors typically have higher capacitance values to provide the necessary torque during startup, while running capacitors have lower capacitance values optimized for continuous operation.

My Take on Capacitors

As a seasoned professional in the world of running sports, I can draw parallels between the role of capacitors in electric motors and the importance of warm-up exercises for athletes. The starting capacitor is like a dynamic warm-up, preparing the motor (athlete) for the upcoming activity by providing an initial push. Once the motor (athlete) is up and running, the running capacitor kicks in to ensure that the performance is maintained at an optimal level throughout the activity or game.


Understanding the difference between starting and running capacitors is crucial for anyone working with electric motors. These small yet vital components play a significant role in ensuring the efficient and reliable operation of electric motors across various applications.