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In Compliance, by Chip Carson PE

Electric Room Protection

Fire Protection and Enclosure Requirements for Electrical Rooms

Reprinted with permission from NFPA Journal® (Vol. 102, #5) copyright© 2008, National Fire Protection Association, Quincy, MI.  All rights reserved.

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 of NFPA 13, Installation of Sprinkler Systems, requires sprinklers in all spaces in a building protected with sprinklers, including electrical rooms. According to Section, 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.

Chip Carson, P.E., is president of Carson Associates, Inc., a fire engineering and code consultancy. He is also a member of NFPA’s Board of Directors.

Reprinted with permission from NFPA Journal® (Vol. 102, #5) copyright© 2008, National Fire Protection Association, Quincy, MI.  All rights reserved.

{ 4 comments… add one }

  • Mike Winkler December 5, 2008, 9:56 am

    The answer is incomplete and accordingly inaccurate because it does not take into account other codes that may apply. The Building Code allows a designer to take advantage of code trade offs by agreeing to install fire sprinklers throughout the building. When this trade off is used, such as in unlimited area buildings, water sprinklers are still required in electrical rooms.

    IBC/MBC section 903. clearly states that water sprinklers shall not be omitted from any room merely because it has electrical equipment. The ICC has published formal interpretations that state the electrical room must also have fire sprinklers.

  • Craig Rauch December 5, 2008, 4:46 pm

    I am not sure I follow all of Mr. Winkler’s comments. I fully agree that the governing building code must be taken into consideration.

    It was, however, my impression that a building would be considered fully suppressed by the IBC even if you omit sprinklers in accordance with the provisions of NFPA 13. In addition would you not consider a building fully suppressed if Item 1,2,3 or 4 of IBC 903. were used?

  • Greg Masters December 8, 2008, 9:07 pm

    Regarding the requirement for dry type transformers over 112.5 kVA to be installed in a 1-hour rated room:

    The article is correct, but leaves out the fact that there are two exceptions to the section (Section 450.21 of the NEC) that contains this requirement. The exceptions are:
    1. Transformers with Class 155 or higher insulation systems and separated from combustible material by a fire-resistant, heat-insulating barrier or by not less than 6 feet horizontally and 12 feet vertically.
    2. Transformers with Class 155 or higher insulation systems and completely enclosed except for ventilating openings.

    I have actually worked with the local electrical inspectors to enforce this requirement in new construction for several years. In many cases, the designers don’t balk, and agree to the 1-hour electrical room with no questions asked. In other cases, they have demonstrated that the installation would meet Exception 2, and we didn’t get the rated room.

  • Brian Dove November 22, 2010, 10:34 am


    To answer your quesiton, no the IFC and IBC are quire clear in their commentary it does not consider a building where sprinklers are ommitted in electrical rooms as being fully sprinklered. This is clearly indicated in 903. of the IBC 2006 and fully supported by the commentary published on this section. In that commentary if the exemption does not fit under one of the 4 exceptions to this section, it is not a fully sprinklered building and all sprinkler tradeoffs are now null and void.

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