University updates fire pump

This case study describes redesigning the electrical system in one of the existing buildings at a university.

03/24/2014


Figure 4: Two different sources supply power to a single-ended substation. The substation feeds all electrical loads of the building including the fire pump. Courtesy: Jacobs EngineeringA project a couple of years ago involved redesigning the electrical system in one of the existing buildings at a university. Even though the building was four stories high, it was not classified as a high-rise as the floor level of the fourth floor was less than 75 ft high. The building was approximately 161,000 sq ft, and housed the university library. After discussions with the client, we decided that the fire pump would be electrically powered and be located adjacent to the main mechanical and electrical rooms, on the ground floor, near one of the entrances to the building.

The building was part of a multibuilding, campus-style complex powered through a radial loop distribution system at medium voltage. The service was then stepped down to 480 V in a new single-ended substation with a duplex primary switch. According to NEC 695.3(C)(1), “Two or more feeders shall be permitted as more than one power source if such feeders are connected to, or derived from, separate utility services.”

Both sources were considered reliable; therefore, we decided that there was no need for another alternate power source for the fire pump. To connect the fire pump controller, we decided to tap into the secondary bus of the substation (see Figure 4). Following 695.4(B), we installed a single disconnecting means and overcurrent protection in the electrical room. The overcurrent device was sized to handle the locked rotor load of the fire pump motor.

Because it was a fully sprinkled building, we decided that exception 695.6(A)(2)(d) applied, which states that “The supply conductors located in the electrical room where they originate and in the fire pump room shall not be required to have the minimum 2-hour fire separation or fire resistance rating…”. We ran the conductors in EMT conduit while in the electrical room and in the fire pump room. The conduit run between the rooms was encased in 2-in. concrete.


Eduard Pacuku is electrical project engineer at Jacobs Engineering, where the majority of his time is spent designing electrical distribution systems for universities (including laboratories), health care facilities, and data centers. He has extensive experience with fire pump installations.



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