Code Quiz of Day

Fire Rating of Door Leading to Transformer Vault

Jan. 5, 2015

Article 450 outlines the installation requirements for transformers and transformer vaults.

Each doorway leading into a transformer vault from the building interior shall be provided with a tight-fitting door having a minimum fire rating of ___ hours.

a) 2
b) 3
c) 4
d) 6

See answer and applicable 2014 NEC reference

The correct answer is: b) 3

Article 450 outlines the installation requirements for transformers and transformer vaults. Part III of this Article covers transformer vaults. As noted in Sec. 45043(A), "Each door leading into a vault from the building interior shall be provided with a tight-fitting door that has a minimum fire rating of 3 hours. The authority having jurisdiction shall be permitted to require such a door for an exterior wall opening where conditions warrant."

About the Author

Mike Holt

Mike Holt is the owner of Mike Holt Enterprises (www.MikeHolt.com), one of the largest electrical publishers in the United States. He earned a master's degree in the Business Administration Program (MBA) from the University of Miami. He earned his reputation as a National Electrical Code (NEC) expert by working his way up through the electrical trade. Formally a construction editor for two different trade publications, Mike started his career as an apprentice electrician and eventually became a master electrician, an electrical inspector, a contractor, and an educator. Mike has taught more than 1,000 classes on 30 different electrical-related subjects — ranging from alarm installations to exam preparation and voltage drop calculations. He continues to produce seminars, videos, books, and online training for the trade as well as contribute monthly Code content to EC&M magazine.