Electrical fire pump with emergency generator
In this case study, an onsite generator must provide the secondary source of power for the fire pump.
The building’s normal power service is supplied from a pad-mounted utility transformer that is fed by a singular utility substation. The authority having jurisdiction has deemed that the single utility service is not considered a reliable source, so it cannot be the only supply source for the fire pump. An onsite generator must provide the secondary source of power for the fire pump. The service to the fire pump will need to meet the requirements as defined by NFPA 70: National Electrical Code (NEC) 695.3(B)(2) for service from an individual source and onsite standby generator.
The primary supply to the fire pump controller will come directly from a connection at the utility transformer. This was coordinated with the utility company; most will allow for this separate connection to be tapped at the transformer. This meets the requirement for continuity of power as defined by NEC 695.4(A) (direct connection). The feeder from the switchgear to the fire pump controller (located in a different area) will be routed below the building floor slab so that it is considered outside the building per NEC 230.6(1).
The second source for the fire pump will come from the emergency power system for the building. The building’s generator system will be sized to handle the starting and normal operating load of the fire pump as defined by NED 695.3(D)(1). A circuit breaker, sized to accommodate normal start-up of the pump, will be located in the emergency distribution board. The second feeder will route overhead to the fire pump controller and be encased in a minimum of 2-in. concrete.
Sarah Kuchera is senior vice president and electrical engineer at ccrd + WSP. Her duties have included project management, production coordination, and project engineering on a variety of different projects including hospital, retail, hospitality, and office buildings.
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