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11. To be in compliance with the NEC, transformer vaults must have a fire-resistance rating of three hours and concrete floors that are at least:

A. three inches thick
B. two inches thick
C. four inches thick
D. one inch thick

unless protected by automatic sprinkler systems.



Answer :

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Final answer:

Transformer vaults need specific fire-resistance ratings and floor thickness to comply with NEC regulations.


Explanation:

Transformer vaults, to comply with the NEC regulations, must have a fire-resistance rating of three hours and concrete floors of a certain thickness unless protected by automatic sprinkler systems. Concrete floors should be at least four inches thick to meet these standards.


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