Supplying power for electric fire pumps
Power is a key element in ensuring a fire pump works in an emergency situation. This article touches on relevant fire codes and offers best practices to illustrate proper design of power for fire pumps.
- Know which codes dictate how to specify power for fire pumps.
- Understand how to coordinate the numerous codes involved.
Electrically powered fire pumps are subject to many national and international codes such as the International Building Code (IBC), NFPA 5000: Building Construction and Safety Code, NFPA 101: Life Safety Code, NFPA 110: Standard for Emergency and Standby Systems, NFPA 20: Standard for Installation of Stationary Pumps for Fire Protection, and NFPA 70: National Electric Code (NEC). Because so many codes are involved, it is important to understand the scope of each code to ensure the correct code is used during the design process.
Fire pump codes
IBC 2009, Section 403, which concerns high-rise buildings, classifies the fire pump as part of the emergency power system. Section 405, which deals with underground buildings (generally buildings that have a level occupied by humans more than 30 ft below the lowest level of exiting the premises), classifies fire pumps as part of the standby power system.
Section 913 of the IBC requires the installation of fire pumps in accordance with NFPA 20. In this case most fire pump rooms must be protected by 2-hour walls. But for non-high-rise buildings that are fully sprinkled, 1-hour walls are acceptable.
NFPA 5000, 2012 Edition
NFPA 5000 classifies fire pumps as part of the standby system (188.8.131.52.4, High-rise buildings). Since no definition is provided for the standby system, this classification can be misconstrued. But 184.108.40.206.1 requires compliance with NEC 701, which concerns the legally required standby system.
Another important requirement of NFPA 5000 is Annex F, In-Building Radio Systems. If the local jurisdiction has specifically adopted this annex, the fire pump room must have radio coverage.
NFPA 101, 2012 Edition
Just like NFPA 5000, NFPA 101 Chapter 11 (special structures and high-rise buildings) requires that fire pumps be part of the standby system and comply with NEC 701. Also, 11.8.6 requires that the emergency command center monitor the fire pump status.
NFPA 110, 2010 Edition
NFPA 110 classifies fire pumps as part of Level I systems, which are essential to the safety of human life (see A.4.4.1). This standard refers to NFPA 20 for the installation of fire pumps.
NFPA 20, 2013 Edition
NFPA 20 covers all stationary fire pumps, but Chapter 6 details electrical fire pumps.
Chapter 6 of NFPA 20 requires that the fire pump be powered by a reliable power source or by two or more independent sources. According to Annex A of NFPA 20, a reliable power source complies with 9.2.3 and has not:
- Had any shutdowns for longer than 4 hours in the previous year
- Experienced power outages that were not caused by natural disasters or grid management failure
- Been supplied by overhead conductors.
NFPA 20 Chapter 9 concerns the performance and testing of electrical equipment between the source and the pump. Even though the fire pumps run infrequently, Chapter 9 requires that all power supplies for the fire pumps be sized based on a continuous duty cycle. Chapter 9 also prohibits the use of phase converters as they are not considered reliable power sources. Thus, it’s necessary to use a single phase motor and fire pump controller if the source is single phase.
Chapter 9 of NFPA 20 describes in detail the overcurrent protection and means of disconnecting a fire pump service. 9.2.3, referenced above, requires the installation of a single disconnecting means and the associating overcurrent protection in the power supply of the fire pump controller. The disconnecting means must be lockable in place to avoid inadvertent power loss and remote from other building disconnecting means.
NFPA 20 also requires an alternate power source for the primary fire pump if the building’s height is beyond the reach of the fire department’s equipment. However, this requirement is waived if a backup pump is installed on the premises. If the alternate power source is a standby generator system, it must have enough capacity to carry the full load of the fire pump and other emergency loads. The generator must also be able to support the fire pump auxiliary system, such as a jockey pump, and have a fuel supply that can provide 8 hours of fire pump continuous operation.
The proper installation of electrical fire pumps and associating equipment is the scope of the NEC. NEC 2011 dedicates Article 695 to fire pumps. Article 695 was first introduced in NEC 1996. Article 695 of NEC also covers the electrical power sources, interconnecting circuits, and switching and control equipment that are dedicated to the fire pump. Jockey (or makeup) pumps are not covered by Article 695.
Although the scope of Article 695 has not changed, important revisions have been made through the years. One of the most important revisions is the requirement of reliable power for electric fire pumps installed in a campus-style arrangement. This arrangement includes multiple buildings often powered by a medium-voltage distribution system.
In case of a campus-style building complex, such as a university, the fire pump can be fed from more than one power source if there are two (or more) feeders derived from two separate utility services. However, this arrangement has to be approved by the authority having jurisdiction before implementation.
NEC 695.3 requires that a reliable power source supply power for an electric fire pump. While NEC does not define a reliable power source, the definition in NFPA 20, described above, can apply. The reliable power source must also be able to carry the locked rotor current of the fire pump motor and the full load current of the accessory equipment if the accessory equipment is connected to the same power source. This reliable power source could be an individual source that in turn could be one of the following:
- Separate utility connection.
- On-site power production facility (that produces power constantly).
- Dedicated feeder.
If the utility power source is not reliable, multiple sources can be used. Alternate sources could be another separate utility feed or a standby generator or both. The generator does not need to be sized for the locked rotor current of the fire pump—only for the full load current of the fire pump(s) and the associating loads. Remember that NFPA 20 Chapter 9 requires the power source to be sized for the continuous duty of the fire pump.
Ensure continuity of power
It is very important that the fire pump is powered continuously and inadvertent power disconnection is averted. To this end, it is preferable that the fire pump controller connects directly to the power supply. However, this connection is not always possible, so 695.4(B) permits the installation of a single disconnecting means and overcurrent protection between the source and the fire pump controller.
NEC 695.6(G) does not permit ground fault protection of the fire pump. Again, this is done to allow continuity of power to the fire pump circuit.
Lock the disconnecting means
Make sure that the disconnecting means is not accidentally exercised, interrupting the power to the fire pump. One way to handle this problem is to lock the disconnecting means in the closed position. Because the disconnecting means might need to be accessed (exercised) during emergency situations, the personnel must know its location. NEC requires a sign placed near the fire pump controller indicating the location of the disconnecting means.
Allow the locked-rotor current
The overcurrent device should be set to allow locked rotor current to flow without tripping. On the other hand, the conductors are sized to no less than 125% of the full load current of the fire pump motor and 100% of the auxiliary loads that the circuit supplies. This standard is different from other NEC requirements in that the rest of NEC requires that the conductors and equipment be protected. In the case of the fire pump circuit, the priority is to keep the pump running no matter what. If a fault occurs, the overcurrent device will trip (which seems to be contrary to what was just stated), but the pump would not work on a short anyway.
Carry only the full load current
The overcurrent protection device between the generator and the fire pump controller is not required to carry the locked rotor load of the fire pump motor. Rather, the overcurrent protection device should be set to carry the full load of the fire pump and the entire auxiliary load fed through the fire pump circuit. The disconnecting means supplied by the emergency generator must also be lockable in the closed position, just like the disconnecting means fed from normal (utility) power.
Design feeding through a transformer
There are cases when a transformer is needed to feed the fire pump circuit. After all, that is why NEC 695.5 exists. The transformer is required to be rated at least 125% of the fire pump and jockey pump loads, plus 100% of auxiliary loads. The primary overcurrent protection device has to be set to allow the locked rotor current of the fire pump and the full load of the associating loads. The secondary overcurrent protection is not allowed.
Account for voltage drop
Another hard requirement of NEC (and also NFPA 20) is that the voltage drop at the fire pump controller be 15% or less. There are several ways to deal with this requirement. Depending on the type of pump, using variable speed drive (don’t forget, the inverter-duty type) eliminates the voltage drop. Another way to mitigate the voltage drop is to size the conductors appropriately.
The conductors supplying the fire pump need to be protected from physical damage. The conductors should be routed outside the building if feasible. If routed inside the building, the conductors have to be encased in 2 in. of concrete. While in the electrical room and in the fire pump room, conductors are not required to have the minimum 2-hour rating, but if the building is a high-rise, consult NEC 700.10(D).
Work with the fire marshal
When designing power for an electrical fire pump, make sure you talk to the fire marshal about the fire pump room location. In the case of a fire, the fire department will enter the pump room to monitor the pump activity, so the pump room needs to be accessible, preferably from the outside.
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.