Which condition most commonly causes streaking on a commutator?

• A. Light electrical load
• B. Light brush pressure
• C. Abrasive dust contamination
• D. Airborne contaminants

Answer: (C)

Streaking on a commutator happens most often when abrasive particles get between the brush and the copper surface. Those tiny particles act like sandpaper as the armature spins, scouring the commutator and creating grooves and a rough look that show up as streaks in the contact area. This contamination disrupts smooth electrical contact and leaves visible marks as the brushes ride over the roughened surface. While light brush pressure or light electrical load can influence wear or contact quality, they aren’t the primary cause of streaking. Airborne contaminants can contribute if they introduce dust, but the direct, common culprit is abrasive dust contamination. Keeping the commutator and brushes clean and free of abrasive particles helps prevent streaking.