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

Correct Answer: Option B — clogged ventilation ducts

Clogged ventilation ducts restrict vital cooling airflow, causing severe localized thermal expansion and insulation breakdown. Under IEEE 45 and 46 CFR Subchapter J, excessive internal temperatures melt soldered connections at the commutator risers, ultimately precipitating an open armature connection fault.