NEIEP Generator Maintenance and Repair (440) Practice Test

The end of a new carbon brush should be seated by lightly sanding it to match the contour of the commutator. This controlled, minimal material removal shapes the brush face so it contacts the curved surface of the commutator evenly, giving good electrical contact and minimizing arcing and uneven wear. Use a fine abrasive and rub the brush on a flat reference while rotating the assembly so the wear is uniform.

Filing or grinding would remove material too aggressively and could create flat spots or gouges, and polishing alone won’t properly shape the brush or remove burrs. Sanding provides the right balance of removing burrs and forming the correct rounded contact surface.