Which motor is enclosed to prevent the free exchange of air between the inside and outside of the case but not sufficiently enclosed to be airtight?

• A. Open Motor
• B. Totally Enclosed Motor
• C. Guarded Motor
• D. Totally Enclosed Nonventilated Motor

Answer: (B)

The concept here is motor enclosure and how it controls air movement around the winding. A motor that is totally enclosed is built so the housing around the motor prevents free air from flowing in or out. It keeps contaminants out and reduces unintended cooling airflow, but it isn’t necessarily perfectly airtight because there can still be small leaks or joints that aren’t perfectly sealed. So this type matches the description of being enclosed to stop free air exchange without being completely airtight.

The other options would not fit as well because an open motor has no enclosure at all, allowing free air exchange; a guarded motor has a protective guard but still permits air movement through openings; and a totally enclosed nonventilated motor is designed to have no ventilation openings, which describes a more tightly sealed condition than what the prompt specifies.