Such conditions cause what issue on commutator bars, leading to fractured brushes?

• A. Color, Flat Spots, Burned Surfaces, and High or Low Bars
• B. Color Only
• C. Flat Spots Only
• D. Burned Surfaces Only

Answer: (A)

When the commutator bars show signs like color changes, flat spots, burned surfaces, or uneven height, it means the electrical and mechanical contact between the brushes and the bars is failing. Color changes indicate overheating from excessive current or poor contact; flat spots show uneven wear as the brush rides on a small area, concentrating wear and heat; burned surfaces come from sustained arcing and scorching at the interface; bars that are higher or lower than others prevent the brush from seating evenly, causing irregular contact. All of these problems disrupt smooth current transfer and create localized heat and mechanical stress on the brushes. That combination accelerates wear and can cause the brushes to fracture or break apart.