How to design safe, reliable fire pump power service
The codes that govern the power supply to the fire pump, as well as conversations with the local authority having jurisdiction, determine the best solution for a building’s fire pump power system design.
- Illustrate the basic design of fire pumps and their power systems.
- Examine the codes and standards that dictate fire pump power system design.
- Explain best practices by reviewing example designs.
As with all life safety systems, maintaining power to the key elements of a building in the event of an emergency is vital to the safety of the building and its occupants. For buildings that do not have an adequate supply pressure from the incoming water source, the fire pump is critical in that protection. Consideration of the power supply to the fire pump and its accessories is based on an evaluation of the codes that govern its installation as well as conversations with the local authority having jurisdiction (AHJ) to determine the best solution for the building's particular design.
In the event of a fire, it is not unusual for first responders to disconnect the main power supply to the building, especially if there is a risk that the source of the fire may be from the electrical system. It is important that the AHJ and the building operator have a clear understanding of how the fire protection system is powered so that the power supply to the fire pump is not inadvertently disconnected. With proper understanding of the codes and good design practice, engineers can ensure the design will provide a reliable source of power for a building's fire protection systems.
Fire pump intent
The fire pump plays a critical role in providing for a safe environment, and how it is powered is an important consideration of the design. A reliable source, backup power supply, protected feeders, and properly sized overcurrent protection are the keys to a successful installation.
Keeping the fire pump operational throughout the entire emergency event is the most important goal of each design. This is even more important than protecting the equipment from harm. If the fire pump fails to perform its intended duty, the building and its occupants will be at great risk.
Codes that apply
Multiple codes apply when it comes to powering fire pumps. Two are primary references: NFPA 70: National Electrical Code (NEC) Article 695 (fire pumps), and NFPA 20: Standard for the Installation of Stationary Pumps for Fire Protection. The NEC has responsibility for the electrical installation of these systems whereas NFPA 20 holds responsibility for the performance of the system. Other articles of the NEC and other NFPA sections offer guidance on emergency power systems and building requirements for fire protections systems.
A reliable power source is necessary for proper fire pump installation. The reliability of a utility service feed for a fire pump will be determined by the local AHJ. Also, depending on the type of building, occupancy type, and the building operator, the method for serving the power to the fire protection systems should be considered as a part of their overall fire-response plan.
As defined by NFPA 20, the following items should be considered to determine if the source is reliable:
- The source power plant has not been shut down for more than 4 continuous hours within the past year.
- There have been no routine power outages in the area that have occurred within the past year.
- The building cannot be served by an overhead utility line. The overhead service line will become a risk because fire department personnel will not work around energized lines. If this overhead line is the source of power, it will become disconnected while fighting the fire and render the fire pump inoperable.
If the utility source is determined to be unreliable, then multiple sources will be needed for the installation.
A single power-supply source for a fire pump can be provided from either a reliable utility supply or from onsite power production. The important consideration for a single supply service is that the incoming supply power is not interrupted. Therefore, special consideration should be given to how the service enters into the fire pump controller and what disconnecting means are located upstream from the pump.
If a utility power connection is used, there are two methods that can provide power to the fire pump:
1. The first method is a direct connection from the utility source where a power feed is brought straight from the utility into the fire pump controller with no interruptions. This feed is then treated as a service entrance and needs to meet all of the code-required functions as defined by NEC Article 230 (services).
2. The second method is a tap ahead of the service main disconnecting means. When using this method, the following items should be considered.
- The service feeders shall terminate in a dedicated cabinet or vertical switchboard section located ahead of and not within the same cabinet as the disconnecting means.
- The service feeder shall be in a location separate from the fire pump so as to minimize the risk of damage to the fire pump in the event of a fire at the main service area.
If onsite power production is available to the building, it can be considered as a service to the fire pump if it is deemed reliable and meets the fire protection requirements as outlined in NFPA 850: Recommended Practice for Fire Protection for Electric Generating Plants and High Voltage Direct Current Converter Stations.
With a single source of power to the pump, if the source that is providing power to the building fails, then a fire watch or other approved procedure needs to be put in place to verify that the building and its occupants are not put into harm's way.