Transformer rooms are not automatically required to be enclosed in fire-rated construction. However, there are situations in which a transformer room may require a fire-rated enclosure.

Where an electrical vault is provided for conductors and equipment operating at over 600 volts, nominal, the vault must be enclosed with a minimum 3-hour fire-rated construction in accordance with NFPA 70. The 3-hour fire-rating is permitted to be reduced to a 1-hour fire-rated construction where the vault is protected with a suppression system.