An incident took place at the end of September at the University of California, Berkeley, you may have heard about in the news. It was the loss of power throughout the campus, due to the removal of copper conductors. It caused the cancellation of all afternoon and evening classes, including one I attend. While this was an inconvenience, it also got me thinking about all the fire alarm systems installed on the campus. Even with the power out, they have to be able to function.
Chapter 10, Fundamentals of NFPA 72, National Fire Alarm and Signaling Code, contains the requirements for primary and secondary power. As we cover this critical topic this month, I will reference the 2013 edition, but the requirements found in this edition do not vary far from the requirements found in a number of prior editions.
Primary, Continual Power Rules
Section 10.6, Power Supplies, is where one is to go within NFPA 72 to find all power requirements for fire alarm systems. The first requirement is found in Paragraph 10.6.3.2, which requires there be two independent and reliable power supplies. The only exception to this is if there is an uninterruptible power supply (UPS) that is configured in compliance with NFPA 111, Standard on Stored Electrical Energy Emergency and Secondary Power Systems. The UPS must be for a Type O, Class 24, Level 1 system.
The primary power requirements are found within Section 10.6.5, Primary Power Supply. The branch circuit providing the primary power is to be dedicated. You may supply power to the fire alarm control unit (FACU) as well as additional power supplies or other auxiliary equipment that is part of the fire alarm systems, such as a voice evacuation control. One may not, however, provide power to other equipment, such as a fax machine, answering machine, desktop computer and so forth.
There are three allowable sources of primary power:
1. Commercial light and power
2. Engine-driven generator, where an operator is on duty at all times, and is specifically trained in the operation of the generator
3. Engine-driven generator that is arranged for cogeneration with commercial light and power, where an operator is on duty at all times, and is specifically trained in the operation of the generator
The branch circuit disconnecting means shall be permanently identified at the FACU. There is a further requirement that the purpose of the system be identified at the disconnecting means, which will typically be the circuit breaker for the circuit. Depending on the type of system, the identifications are:
1. FIRE ALARM, for a fire alarm system
2. EMERGENCY COMMUNCATIONS, for an emergency communications system (mass notification)
3. FIRE ALARM / ECS, for a combination fire alarm and emergency communications system
The circuit disconnecting means shall also have a red marking. DO NOT paint the circuit breaker red, or apply red nail polish. This will violate the listing of the breaker. A new paragraph (10.6.5.2.4) was added to the 2013 edition on this topic: “The red marking shall not damage the overcurrent protective devices or obscure the manufacturer’s markings.”
Section 10.6.6, Continuity of Power Supplies, requires that the transfer from the primary to the secondary source be accomplished within 10 seconds. This section also contains a requirement that any signals from the system not be delayed by more than 10 seconds as the result of a primary power failure.
Secondary Power Guidelines
In the event that took place at UC Berkeley, the power was out, and out for a substantial time. Section 10.6.7 covers Secondary Power Supplies. The principal requirement and duty of the secondary power supply is to maintain the operation of the system. The larger the capacity of the secondary power supply, the longer the system may operate without primary power.
In prior editions of 72, there was a requirement for either 24 hours of standby for central station service, local or proprietary systems; or a requirement for 60 hours for remote station or auxiliary systems. This was changed several cycles ago, to the requirement that all systems be able to operate under the quiescent load for a minimum of 24 hours, and then be capable of operating all of the notification appliances for five minutes, or 15 minutes for a voice system. Mass notification or ECS systems are also required to be able to operate for the 15-minute timeframe.
The key word within in Paragraph 10.6.7.2 is, “minimum.” Depending on the type of system or the location of the system, there may be consideration to having the standby capacity extended. This may be through a risk analysis of the system designer, a decision by the owner or by direction of the authority having jurisdiction (AHJ).
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Dr. Shane Clary
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