Light electrical load causes commutator ______.

• A. Threading
• B. Arcing
• C. Pitting
• D. Vibration

Answer: (A)

Under light electrical load the current is small, so sparking and arcing are minimal. The wear becomes more about the mechanical rubbing between the brushes and the commutator surface. The brush edge can gradually cut a narrow, helical groove around the circumference as the rotor turns, producing a thread-like pattern. This threading is a wear phenomenon caused by contact rather than electrical faults. To address it, check brush seating and pressure, ensure proper alignment, and consider dressing or resurfacing the commutator and brushes if needed. Arcing, pitting, and vibration are typically linked to heavier load, misalignment, or mechanical looseness, not this light-load wear pattern.