Grooving on a commutator is caused by which factor?

• A. Abrasive brush
• B. Abrasive dust contamination
• C. Improper brush spacing
• D. Electrical wear from too light brush pressure

Answer: (A)

Grooving on a commutator happens when abrasive material at the contact point removes copper as the commutator rotates against the brush. If the brush itself is abrasive, or contains grit, it can act like a cutting tool, digging into the copper surface and leaving grooves. The brush should be softer than the copper, so wear happens mainly on the brush rather than the commutator; when the brush is abrasive, it wears into the commutator and creates grooves. While dust or contamination can speed wear, the direct cause of grooves in this scenario is the abrasive brush acting at the sliding interface.