Designing for Code Compliance

As an electrical contractor, you understand the need and use of power for all electrical appliances, but do you understand the specific power requirements, both primary and secondary, for all of the fire alarm systems outlined in NFPA 72 2010, the National Fire Alarm and Signaling Code?

Of course, the first requirement states that you must install all power supplies in conformance with NFPA 70 2012. Additionally, unless an uninterruptible power supply (UPS) powers the fire alarm system, it must have a primary and a secondary independent, reliable power supply. The system must monitor all power supplies for integrity in accordance with the code.

Generally, a dedicated branch circuit of one of the following must supply primary power:

1. Commercial light and power
2. An engine-driven generator or equivalent or an engine-driven generator or equivalent arranged for cogeneration with commercial light and power in accordance with specific code requirements, where a person specifically trained in its operation is on duty at all times.

If a fire alarm system uses a UPS, you must configure the UPS to comply with NFPA 111, the Standard on Stored Electrical Energy Emergency and Standby Power Systems, for a Type 0, Class 24, Level 1 system. You must supply the UPS from a dedicated branch circuit. UPS failure must result in the initiation of a trouble signal.

Each of these power supplies must also have “adequate capacity” for the application, meaning the design of the fire alarm system primary supply will allow it to properly power all devices during a normal, nonalarm state; it must also power all code-required appliances during the alarm state. The code requires all notification appliances to operate in alarm for at least 5 minutes, but you must include all relays that must operate in an alarm condition in the power calculations.

The code has different requirements for in-building fire emergency evacuation systems and for mass notification systems (MNS). In these two cases, the power supply must have sufficient capacity to operate all notification appliances and alarm relays for 15 minutes under full-load conditions.

Primary power sources must have their circuit connections identified and must remain accessible. The location of the dedicated branch-circuit disconnecting means must be permanently identified at the fire alarm control unit and marked “FIRE ALARM CIRCUIT.” In addition, the circuit disconnecting means must have a red marking, be protected against physical damage and be accessible only to authorized personnel. Essentially, the circuit breaker panel must either be locked or be located in a locked electrical room. A locked circuit breaker within an electrical panel that serves as the disconnecting means for the fire alarm system power also meets this requirement.

Secondary power for all systems must operate the entire system in a nonalarm state for 24 hours and then perform the alarm functions as outlined previously for each type of system.

In most cases, you will use batteries—-supplied by the fire alarm system manufacturer—as the secondary power source. Underwriters Laboratories does not typically list batteries, but they become part of the listing the fire alarm control unit receives when the manufacturer submits the FACU and batteries for testing and listing. You must protect secondary circuits that provide power to the control unit—and are not integral to the unit—against physical damage in accordance with the National Electrical Code (NEC).

When batteries serve as the secondary power source, NFPA 72 2010 requires the battery calculations to include a 20 percent safety margin in the calculated amp-hour rating. The code requires the manufacturer to mark the batteries with the month and year of manufacture using the month/year format. When the manufacturer has not marked the batteries with the month/year, the contractor must obtain the date code from the supplier or manufacturer and mark each battery with the month/year of battery manufacture.

A UPS for remotely located control equipment, circuit interfaces or other equipment essential to system operation must consist of a primary and secondary power supply that meets the same requirements as the main fire alarm control unit. The installing contractor must identify the locations of the remotely located equipment at the master control unit. Although not part of the power supply requirements, the code also requires that the contractor install a smoke detector at every location of a fire alarm control unit/power supply and all remote power supplies.

An emergency generator may also supply secondary power for a fire alarm system. In such a case, the code requires an automatic-starting, engine-driven generator to serve the dedicated branch circuit and to supply power for storage batteries. In addition to the generator, storage batteries dedicated to the fire alarm system must supply 4 hours of capacity arranged to operate the system in a nonalarm state and, at the end of the 4 hours, operate the system in an alarm state for 5 minutes. This provides a backup in case the generator does not start and provides 4 hours to make repairs to the generator.

Understanding these power requirements of NFPA 72 2010 will help you avoid extra installation costs.

MOORE, a licensed fire protection engineer, frequent speaker and an expert in the life safety field, is a past chair of the NFPA 72 Technical Correlating Committee. Moore is a principal with Hughes Associates Inc. at the Warwick, R.I., office. He can be reached at

About the Author

Wayne D. Moore

Fire/Life Safety Columnist
Wayne D. Moore, a licensed fire protection engineer, frequent speaker and an expert in the life safety field, is a principal member and past chair of NFPA 72, Chapter 24. Moore is a vice president with JENSEN HUGHES at the Warwick, R.I., office. He c...

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