Which condition can cause brushes to stick in their holder?

• A. Brush grade unsuitable for machine
• B. Brushes sticking in holder
• C. Bearing wear
• D. Airborne contaminants

Answer: (B)

The thing being described is binding friction inside the brush holder. When the carbon brushes don’t move freely, they can seize or bind in the holder, which is the direct condition that causes brushing to stick. This binding often happens when debris or carbon dust accumulates, or the brush itself swells or carbon material deforms from heat or moisture, reducing the clearances the holder is designed to provide. The spring pressure then can’t push the brush smoothly, so it sticks against the holder slot or the commutator.

Other factors can contribute indirectly—using the wrong brush grade can lead to abnormal wear or poor contact, bearing wear can misalign the assembly and change how the brush seats, and airborne contaminants can introduce carbon dust or moisture that encourages sticking—but the immediate cause of the sticking is the brushes binding in their holder.