The minimum size of transformer vault ventilation openings for transformers rated less than 50 kVA is ___ square feet.

• A. 2
• B. 3
• C. 4
• D. 1

Answer: (D)

In transformer vaults, ventilation openings must provide enough air exchange to dissipate heat and vent any gases from oil-filled transformers. For transformers rated under 50 kVA, the required minimum total ventilation opening area is 1 square foot. This is the smallest size that meets the safety need for such a unit; larger transformers require larger openings, so 2, 3, or 4 square feet would apply to bigger ratings rather than under 50 kVA.