NFPA Journal®, September/October 2008

There seems to be much confusion concerning the fire protection and enclosure requirements for electrical rooms. Do rooms containing circuit breaker panels or transformers need to be enclosed in fire-resistive enclosures? Do these rooms require sprinklers, or should sprinklers be eliminated in these rooms?

Electrical rooms are not listed as hazardous areas in Chapter 8 of NFPA 101®, Life Safety Code®, or in Sections 3.2, “Protection from Hazards,” in each occupancy chapter. Rather, the requirements for enclosures in electrical rooms are found in NFPA 70®, National Electrical Code® (NEC®).

NEC Article 450.21 “Dry-Type Transformers Installed Indoors,” requires that dry-type transformers rated larger than 112-1/2 kVA be installed in a transformer room of fire-resistive construction. In this Article, the term “fire-resistive” means a one-hour fire resistance. The door to this room would be a 45-minute fire-protection-rated, self-closing, latching door.

Dry transformers over 35,000 volts must be enclosed in a vault. Vault construction, which is addressed in Article 450.42, requires a three-hour fire-resistance rating, although an exception permits a one-hour fire-resistive enclosure where the transformer is protected with a fixed extinguishing system, such as sprinklers, or a gaseous agent extinguishing system.

NEC Article 450.26 addresses oil-insulated transformers installed indoors. Such transformers may be installed in buildings of Type I or II construction if the transformer is rated 35,000 volts or less, no combustible materials are stored in the area, a liquid confinement area is provided, and the  installation complies with all restrictions provided for in the listing of the liquid. Oil-insulated transformers can also be installed indoors if they are protected with an automatic fire extinguishing system and a liquid confinement area, provided the transformers are rated 35,000 volts or less. And oil-insulated transformers can be installed in a vault. Unless the transformer is rated at less than 112-1/2 kVA, however, the vault must be constructed of reinforced concrete at least 4 inches (10 centimeters) thick. If the transformer’s nominal voltage is less than 600, a vault is not required if arrangements have been made to prevent a transformer oil fire from igniting other materials and if the total capacity in one location does not exceed 10 kVA in a section of the building classified as combustible or 75 kVA where the surrounding structure is classified as fire-resistant construction.

Electrical equipment other than the transformers covered in Article 450 containing more than 10 gallons (38 liters) of flammable oil per unit must meet the requirements of Parts II and III of Article 450, which may require a fire-resistive enclosure. There are also special requirements for special electrical installations, such as charged-particle-accelerating equipment and surface mining equipment.

So if rooms containing typical circuit breaker panels and small dry transformers do not require any special fire-resistive enclosures, what about sprinklers in these rooms?

Section 8.15.10.1 of NFPA 13, Installation of Sprinkler Systems, requires sprinklers in all spaces in a building protected with sprinklers, including electrical rooms. According to Section 8.15.10.3, however, sprinklers may be eliminated in electrical rooms if the room is dedicated solely to electrical equipment; only dry-type electrical equipment is used; the equipment is installed in a two-hour fire-rated enclosure including protection for penetrations; and no combustible storage is permitted in the room.

In general, typical electrical rooms containing circuit breaker panels and dry transformers do not require a special fire-resistive enclosure, but electrical rooms in sprinklered buildings do require sprinklers. However, special high-voltage electrical equipment and oil-filled equipment may require additional protection in accordance with the NEC.