Minimum fire rating for materials used in housing a dry-type transformer rated over 112.5 kVA is 1 hour.

Minimum fire rating for materials used in housing a dry-type transformer rated over 112.5 kVA is 1 hour.

• A. 1 hour
• B. 3 hours
• C. 2 hours
• D. 6 hours

Answer: (A)

Fire-resistance ratings for enclosures around electrical equipment show how long the surrounding materials can withstand exposure to fire without failing. For dry-type transformers, the requirement scales with the transformer’s size. When the transformer is rated over 112.5 kVA, the materials used in housing it must have at least a one-hour fire rating. This level provides a basic, practical measure to contain a potential fire and protect adjacent equipment and occupants, without mandating a higher rating that isn’t required at this size. The other durations (two, three, or six hours) exceed the minimum needed for this rating category, so they aren’t the required standard for this size.

Fire-resistance ratings for enclosures around electrical equipment show how long the surrounding materials can withstand exposure to fire without failing. For dry-type transformers, the requirement scales with the transformer’s size. When the transformer is rated over 112.5 kVA, the materials used in housing it must have at least a one-hour fire rating. This level provides a basic, practical measure to contain a potential fire and protect adjacent equipment and occupants, without mandating a higher rating that isn’t required at this size. The other durations (two, three, or six hours) exceed the minimum needed for this rating category, so they aren’t the required standard for this size.