Besides a condition of overload, what could be a cause of an open armature connection in a DC propulsion motor?

Correct Answer: Option A — clogged ventilation ducts

Clogged ventilation ducts restrict airflow, leading to localized overheating of the armature windings. This thermal stress degrades insulation, eventually causing internal shorts or open circuits. Per 46 CFR Subchapter J, maintaining adequate cooling is critical to prevent the thermal breakdown of insulation systems in high-load propulsion motors.