Understanding Power Requirements

Many electrical contractors (ECs) run the primary power to fire alarm control units without giving the installation much thought. After all, they have done this type of installation numerous times, and most could perform the operation blindfolded. The National Fire Alarm Code does, however, have specific requirements that must be followed in addition to the requirements of the National Electrical Code (NEC).

First, Section of NFPA 72-2007 requires that a dedicated branch circuit be provided by one of the following:

“(1) Commercial light and power

“(2) An engine-driven generator or equivalent in accordance with, where a person specifically trained in its operation is on duty at all times

“(3) An engine-driven generator or equivalent arranged for cogeneration with commercial light and power in accordance with, where a person specifically trained in its operation is on duty at all times.”

These dedicated branch circuit(s) and connections must be mechanically protected, and Section requires that the circuit disconnecting means have a red marking, shall be accessible only to authorized personnel and shall be identified as “Fire Alarm Circuit.”

Additionally, Section of the code requires that the location of the circuit-disconnecting means be permanently identified at the fire alarm control unit (FACU). Typically, a contractor will identify the location of the primary power disconnecting means using a permanent marker inside the FACU, but obviously the marking should be legible to meet the intent of the code.

The secondary power supply for a fire alarm system usually consists of a battery standby configuration. However, if an automatic-starting, engine-driven generator is used to provide secondary power for a protected premises fire alarm system, it must comply with NFPA 110, Standard for Emergency and Standby Power Systems, Chapter 4, requirements for a Type 10, Class 24, Level 1 System. In addition to the generator, the fire alarm system must have storage batteries dedicated to the fire alarm system with four hours of capacity. Of course, the installation of the generator must be in accordance with NEC Article 700.

The standby power must be of sufficient capacity to operate the fire alarm system under quiescent load (system operating in a nonalarm condition) for a minimum of 24 hours and, at the end of that period, must be capable of operating all alarm notification appliances used for evacuation for five minutes.

If the secondary power supply is for emergency voice/alarm communications service, then it must be capable of operating the system under quiescent load for a minimum of 24 hours and then must be capable of operating the system during a fire or other emergency condition for a period of 15 minutes at maximum connected load.

Although not high on the radar screen of most contractors, when installing power circuits that serve fire alarm equipment where the survivability of circuits is required by Chapter 6 of the code, equal survivability protection must be provided for the power supply circuits. This could be an expensive oversight by a contractor. These circuits often will be required to use circuit integrity cable or circuit integrity cable in conduit, which is more expensive than standard power-circuit wiring.

Most fire alarm systems installed today require additional power supplies that are remote from the FACU. When these additional power supplies are provided for control units, circuit interfaces or other equipment essential to system operation and located remotely from the main control unit, the primary and secondary power supplies must meet the same requirements as the power supply requirements for the main fire alarm control unit. Also, the location of any remotely located power supply must be identified at the master control unit as well as on the record drawings. Transient protection is required on all fire alarm systems to reduce the possibility of damage by induced transients for all fire alarm circuits and equipment. Circuits and equipment must be properly protected in accordance with the requirements of NEC Article 800.

Finally, for those of you who design the systems you install, the Code has additional requirements you should observe regarding the protection of fire alarm system control equipment. Section 4.4.5 requires that in areas that are not continuously occupied, automatic smoke detection must be provided at the location of each fire alarm control unit(s), notification appliance circuit-power extenders and supervising station transmitting equipment to provide notification of fire at that location. The exceptions to this requirement state:

• “Exception No. 1: Where ambient conditions prohibit installation of automatic smoke detection, automatic heat detection shall be permitted.

• “Exception No. 2: Fully sprinklered buildings shall not require protection in accordance with 4.4.5.”

Of course, if the ambient conditions are not good for smoke detection, the wise contractor should reconsider the fire alarm control unit location because it is listed to many of the same ambient conditions as smoke detectors.

Remember that the NEC is not the only code that electrical contractors need to know. Avoid costly mistakes by reading and understanding the National Fire Alarm Code.

MOORE, a licensed fire protection engineer, frequent speaker and an expert in the life safety field, is a co-editor of the current National Fire Alarm Code Handbook. Moore is a principal with Hughes Associates Inc. at the Warwick, R.I., office.

About the Author

Wayne D. Moore

Fire/Life Safety Columnist

Wayne D. Moore, a licensed fire protection engineer, frequent speaker and expert in the life safety field, is a principal member and past chair of NFPA 72, Chapter 24. He is a vice president with Jensen Hughes at the Warwick, R.I., office and can be...

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