Power for fire pumps
Power is a key element in ensuring a fire pump works in an emergency situation.
- Learn the basics of designing electrical power system to feed the fire pump system.
- Understand the basic principle behind fire pump electrical power systems.
- Know the codes that pertain to providing power to fire pumps, chiefly NFPA 20 and NFPA 70, and know how NFPA 1, NFPA 101, NFPA 110, NFPA 5000, IBC, and IFC pertain to fire pump designs.
There are few pieces of equipment in a building more critical than the fire pump. Although it will hopefully never run for its intended purpose, when there is that dreaded fire in a building, the fire pump must work. A failure in the fire pump system endangers people’s lives. Because of the critical nature of a piece of equipment that rarely runs, the engineer designing the system must fully understand the codes and standards, and use his engineering judgment to provide a robust system that will operate during the most critical of times.
When designing the power supply for a facility fire pump, there are specific code requirements that apply and must be followed. The two main code sections for providing power to fire pumps are NFPA 20: Standard for the Installation of Stationary Pumps for Fire Protection Chapter 9 and NFPA 70: National Electric Code (NEC) Article 695. Although there is some overlap between the two codes, there are differences in the scopes of the two articles, as they both state right up front. Article 695 covers the requirements for the electric installation. NFPA 20 covers the fire pump selection and installation. NFPA 20 also covers reliability concerns for the power supplies, which is where most of the overlap with Article 695 occurs. Fortunately, Article 695 references NFPA 20 extensively, minimizing the code-hopping that engineers are so fond of.
Before we start discussing technical details, the first step to designing the power for a fire pump system is to coordinate with the architect and fire protection engineer on whether a fire pump is required, and if so, what size will it be. The architect will review the building type and number of occupants to determine if a sprinkler system and fire pump are required. He or she also will review the locally adopted codes such as the International Building Code (IBC), International Fire Code (IFC), NFPA 5000: Building Construction and Safety Code, NFPA 101: Life Safety Code, and any other specifications, local codes, or amendments to the codes.
Specific references to fire pump requirements are sprinkled throughout these codes, and almost all reference NFPA 20. IBC Chapter 913 is dedicated to fire pump requirements and deals essentially with protection of the fire pump room within the building. In Chapter 403.4.9 the IBC defines electric fire pumps as emergency loads. IFC Chapter 913 deals specifically with fire pumps and the room requirements. NFPA 5000 briefly references fire pumps, requiring that the fire pumps in high-rise buildings be fed from the emergency system and monitored from the emergency command center. To reserve space for electrical equipment and fire pump controllers, coordinating early with the architect is critical. There are some battles you have to continually fight, and you will have better luck the earlier you start.
The fire protection engineer will review the existing water pressure and determine, if required, what type and size the pump will be. He or she will review and design to NFPA 20, NFPA 1: Fire Code, NFPA 72: Fire Alarm and Signaling Code, and any other specifications, local codes, or amendments to the codes. NFPA 1 Section 13.4 lists requirements for fire pumps. These are primarily taken from NFPA 20 and relate to the design of the fire pumps. NFPA 1does not deal specifically with power to fire pumps. NFPA 72 lists monitoring requirements for fire pumps by the fire alarm system.
NEC Article 695 starts appropriately with the requirements for the power source for electric motor. Where the power source is determined to be reliable, only one source of power is required. NFPA 20 Annex A gives clear direction as to what is determined reliable. The source cannot have had more than a 4-hr shutdown in the previous year. So, if the project is a new building, the local utility will need to be contacted to determine what outages occurred in the past year. Also, the service connection cannot be from an overhead service. Finally, more than one disconnect cannot be installed on the service conductor.
A single reliable source of power can be furnished by one of three methods:
- A dedicated service from the utility, or a tap ahead of the normal utility service disconnecting means.
- An “on-site power production facility.” This is a facility that is continuously running. A standby generator does not meet this requirement.
- A dedicated feeder from a dedicated utility service. It should also be noted that phase converters are not permitted. Phase converters convert a single-phase service into a 3-phase service, but due to the voltage imbalance they cause, they can have a negative impact on the fire pump controller.
In practice, the most commonly used single source for a fire pump is the tap off the electrical service. To meet NEC requirements, this has to be ahead of the main electric service; has to be in a different cabinet, enclosure, or vertical switchboard/switchgear section from the service; and is required to minimize the possibility of damage from fire. It’s a good idea to locate the tap enclosure in a different area or even a separate room from the main electrical service equipment, so that a fire at the main electrical equipment will not affect the fire pump service.
Where a single source of power does not meet the reliability requirements, a second alternate source of power must be provided. The alternate source of power may be a combination of the single source options. The alternate source may also be a standby generator. Finally, a diesel or steam-driven backup fire pump is allowed to substitute for an alternate electric source.