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Authorities and Requirements

Fire Alarm System Fundamentals

Power Supplies

As power is a fundamental component of the fire alarm system, the requirements for power supply arrangement are contained in the “Fundamentals of Fire Alarm Systems” chapter. The only exception to this involves residential fire alarm systems. The power supply arrangement for residential systems is contained in a separate chapter of NFPA 72Chapter 11 is titled "Single and Multiple-Station Alarms and Household Fire Alarm Systems." As this chapter is very specifically applied to residential occupancies, it virtually stands alone in many of its requirements.. Residential fire alarms are the subject of another section of this program.

Both a primary and secondary power supplyIn older fire alarm installations, there was a requirement for three power supplies: primary, secondary, and trouble. An exception in the fire alarm standard allowed the use of a single power supply for both the secondary and trouble. As manufacturers increased the technical ability of their equipment, the exception became the rule and design changed to reflect two power supplies, dropping the requirement for the trouble power supply. There may still be systems in the field that have the third power supply installed.    are required for all fire alarm systems. Requirements of each are outlined the Fundamentals chapter. A statement in this chapter also directs you to the requirements of the NEC. As one would expect, each of these supplies has to be able to fully carry the electrical load of the fire alarm system.

Primary power supplies are typically a normal light and power connection to the public utility. Secondary supplies are usually batteries as part of the fire alarm control panel. In both cases, other arrangementsThere are places in the world where fire alarm systems do not have access to what most consider an acceptable public utility supply. For example, there are American-operated schools in third world countries that derive their power from generators. This is the "acceptable" primary power supply for these systems. are allowed. The power supplies have to be monitored for the presence of voltage but not their actual voltage levels. A trouble signal is generated if the power from either supply falls below an acceptable level.
NOTE: This is an unformatted excerpt from our online fire protection training library.

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