Q My question pertains to an installation in Fairfax County, Va. that still follows the 1996 NEC. We have a project where the main electrical service is located in the same room as the controller/disconnect for a fire pump. The fire pump controller is located 6 feet from the main service switchboard, and is fed by dual sources, the normal power and an emergency generator.
Is the 6-foot physical spacing acceptable and does it need to be in a separate room, or can it be in a separate space? Can the controller be located in an area behind a 6-foot block wall that is open on top, so that it is still part of the same electrical room?
The 1996 NFPA Handbook for the NEC shows an illustration of a generator dedicated to the fire pump. It describes a direct connection in Section 695-4(b). Is this the intent of the Code? We typically will design a generator service, by bringing the emergency feeder into a distribution panelboard and feed sub-feeders from that panelboard to various emergency loads through automatic transfer switches, such as elevators, egress lighting and the fire pumps. We typically will size the fire pump emergency service to be at 250% of the full load requirements of the pump motor. Is that also within Code?
Does the direct connect requirement of the Code really necessitate a dedicated emergency generator service to the fire pump?
A As noted in the commentary of the 1996 NEC Handbook, neither the NEC nor NFPA 20 require a dedicated room. NFPA 20 does describe a suitable space. Certainly it can be in the same room, perhaps separated by a partition or barrier, but even a barrier is not necessarily required. There must be sufficient separation to minimize the possibility that some accident in the normal service will also compromise the fire pump installation. The AHJ should be consulted in individual cases.
The NEC requires a reliable source of power for a fire pump.
In some jurisdictions, the utility source may be judged to meet this requirement. However, in many situations, an on-site source is also required. A generator used to supply a fire pump need not be dedicated to the fire pump, but the direct connection requirement you refer to (Section 695-4(b) in the 1996 NEC) would require a separate transfer switch for the fire pump, usually as part of a listed combination fire pump controller and transfer switch. This usually also requires a separate feeder, perhaps separately routed, from the generator to the fire pump transfer switch.
Your 250% rule may or may not provide adequate capacity for the fire pump. The capacity of the feeder conductors is only required to meet the normal 125% requirement for motors in general. However, the overcurrent device should be selected to provide short-circuit and ground-fault protection only and the controller is not permitted to provide overload protection.
The overcurrent device must allow the locked-rotor current to continue indefinitely. This is better covered in the 1999 NEC. However, users of either the 1996 or 1999 NEC should also refer to NFPA 20, Standard for Installation of Centrifugal Fire Pumps. See Appendix A for specific references to NFPA 20 that are extracted and included in the NEC.