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

Sparking at the brushes of a DC motor is frequently caused by the brushes being located outside the magnetic neutral plane. This results in commutation occurring while the armature coils are still cutting magnetic flux, inducing high voltages that cause arcing. Proper brush rigging alignment is essential for sparkless commutation.