You’re reading an outdated article. Please go to the recent issues to find up-to-date content.
Recently, I fielded a question about the basic statement in Section 695.3 of the 2008 National Electrical Code (NEC) that “electric motor-driven fire pumps shall have a reliable source of power.” The question involved the reliability of the power source for one of the most important electrical motors in a building. The NEC does not seem to provide any specific guidance on this subject, but Section 9.3.2 in the National Fire Protection Association 20, the 2007 edition of the Standard for the Instal-lation of Stationary Pumps for Fire Protection, provides information when the source of power is not reliable, including addi-tional explanations in A.9.3.2 in Annex A as well as a reference to 9.3.3.
Section 9.3.2 of NFPA 20 states, “Except for an arrangement described in 9.3.3, at least one additional source of power is required for the electrical fire pump where a normal source of power is not reliable.” The additional source of power 9.3.2 alludes to would be a gen-erator or some other source of generated power, such as an emergency or standby generator. In Section 9.3.3, this alternate source of power is not required where the electric fire pump has a backup engine-driven fire pump of gasoline, diesel, natural gas or other fuel, or the backup fire pump is a steam turbine.
Section A9.3.2 in Annex A in NFPA 20 does provide substantially more information on the reliability of the power source by provid-ing four characteristics of a reliable source of power. The first characteristic would be a source power plant that has not experienced any power loss longer than four continuous hours in the year prior to submitting the design plans of the fire pump system. The four-hour requirement originates in NFPA 25, the Standard for the Inspection, Testing, and Maintenance of Water-Based Fire Protection Systems, where special undertakings, such as fire watches and similar measures, must be implemented where the water-based fire protection sys-tem is taken out of service for more than four hours. If the normal source of power from the power plant has been intentionally shut down for longer than four hours, an alternate source of power can be required.
The second characteristic in A.9.3.2 explains that NFPA 20 does not require that the normal source of power to the electric fire pump be infallible and does not intend to require a backup source of power for every installation using an electric motor-driven fire pump. If there are power outages experienced in the area of the protected facility caused by failures in the power grid due to natural disasters (such as hurricanes, tornadoes and similar natural disruptions) or electric grid management failures (such as regional blackouts), the fire protection system could be supplied by a fire department connection, negating the requirement for the fire pump. However, Section 9.3.1 points out that the height of a building or structure may be beyond the pumping capacity of a fire department apparatus, and in those cases, an alternate source of power would be required for the fire pump. Also, if the power grid were known to have regular switch failures, substation loss of power from animal intrusion, or similar causes of failure in the past, providing an alternate backup source of power for the electric fire pump would be necessary.
The third characteristic involves overhead power lines installed to the protected premises. Fire departments responding to an incident at the protected premises normally will not operate aerial ladders and other apparatus close to energized overhead power lines. In many cases, the electric utility company often will remove power from the facility and from the overhead lines by physically cutting the overhead lines or disconnecting the power at the substation, so the fire department can safely fight the fire. Removing normal power on the overhead lines sup-plying power to the facility may inadvertently disconnect power to the electric fire pump, necessitating an alternate source of power to the electric fire pump.
The fourth characteristic ensures only one disconnecting switch and overcurrent protection device be provided for the electric fire pump. The power disconnection and overcurrent protection should be located at the fire pump controller and be supplied by one of the five permitted normal sources of power in 9.2.2 of NFPA 20. Where there are additional disconnecting means or overcurrent protective devices installed between the normal source and the fire pump controller, there is a greater likelihood that inadvertent disconnection of power can occur, and an alternate power source should be provided.
The information in Article 695 in the NEC can be augmented by the information provided in NFPA 20 for the electrical supply to a fire pump.
ODE is a staff engineering associate at Underwriters Laboratories Inc., in Research Triangle Park, N.C. He can be reached at 919.549.1726 and [email protected].