Electrician Red Seal · Question
An electrician is inspecting the brushes and commutator of a DC motor. What signs indicate normal wear and proper operation?
A healthy commutator will develop a smooth, dark, polished film (patina) over time, which provides both lubrication and good electrical contact for the brushes,
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Question: An electrician is inspecting the brushes and commutator of a DC motor. What signs indicate normal wear and proper operation?
Answer options: ✅ Brushes seated well against the commutator with a dark, polished, chocolate-brown film (patina) on the commutator segment surfaces.
- Brushes showing signs of excessive arcing and pitting on the commutator surface.
- Commutator segments that are black, rough, and uneven.
- Brushes that are sticking in their holders and not making continuous contact.
Correct answer: Brushes seated well against the commutator with a dark, polished, chocolate-brown film (patina) on the commutator segment surfaces.
Explanation: A healthy commutator will develop a smooth, dark, polished film (patina) over time, which provides both lubrication and good electrical contact for the brushes, reducing wear. Signs of arcing, pitting, roughness, or blackening indicate abnormal operation, often due to overloaded brushes, improper tension, or contamination. Brushes sticking in holders will lead to intermittent contact and arcing.
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