When is it recommended to replace old brushes with new ones in electric motors?

Replacing brushes in electric motors is crucial for maintaining optimal performance and reliability. The recommendation to replace brushes when they are worn to 40 percent is grounded in the understanding of the operational efficiency and longevity of the motor.

At this point of wear, the brushes may start to lose their effectiveness in conducting electricity, which can lead to poor motor performance, increased sparking, or even damage to the commutator. By replacing the brushes at 40 percent wear, you ensure that the motor continues to operate smoothly and prevents any further wear and tear on the commutator itself, thus extending the overall lifespan of the motor.

Waiting until 50 percent or even 60 percent wear could risk encountering issues that might affect the motor's functionality and efficiency. Therefore, the 40 percent threshold strikes a balance between maximizing brush life and ensuring the motor operates effectively.