In addition to improper brush pressure or seating, what can result in excessive sparking at the brushes of a DC propulsion motor?

Correct Answer: Option A — improper positioning of brush rigging outside the neutral plane

Brush rigging shifted away from the neutral plane experiences transformer voltages in the commutated coils, causing severe and destructive sparking. Proper mechanical positioning is mandatory under 46 CFR and IEEE 45 standards for DC propulsion.