Air-cooled/dry transformers encased in a room that is not sprinklered are rated at how many hours?

The correct answer is 3 hours because air-cooled or dry-type transformers are required to meet specific fire-resistance ratings when they are located in non-sprinklered spaces. These transformers, when encased in a protective room, must have a fire rating that allows for sufficient containment of potential fires that may arise within the room. A rating of 3 hours is commonly mandated to ensure that in the event of a fire, there is ample time for evacuation and for firefighters to reach the scene without the fire spreading to adjacent areas. This rating is part of the fire protection strategy to mitigate the risks associated with electrical faults and overheating in transformer operations, especially in environments where automatic suppression systems are not available.