Fire Alarm Backup Power

April 14, 2011
ByFire Engineering Staff

Article and photos by Gregory Havel

Because of changing technology and advances in electronics, it sometimes seems that no two fire alarm systems are alike. Even though some systems may be newer and more sophisticated than some older models, they all have similar basic functions and controls. Photo 1 shows the control panel for a zoned-protected premises fire alarm system which was installed in the early 1990s. 

(1)

  • The far-left quarter of the upper section of this control panel contains trouble indicator lamps and a single lamp indicating that the primary power supply is functioning.
  • The left half of the lower section contains system control switches, including “Trouble Silence,” “Alarm Silence,” and “System Reset” buttons.
  • The center two quarters of the upper section and the right half of the lower section contain trouble- and alarm-indicator lamps for each of the alarm-initiating zones.
  • The far-right quarter of the upper section contains an isolation switch for each of the active-alarm initiating zones. These switches allow a single zone to be temporarily isolated from the control panel for cleaning and maintenance of devices like smoke detectors. Isolating a zone will cause a visual and audible trouble signal at the panel, which will remain active until the zone isolation is cancelled.
In newer and more sophisticated (digital) alarm systems, the indicator lamps or LEDs are often replaced by customized text messages, and the individual control switches may be replaced by an alphanumeric keypad or a computer terminal. The zones of neighboring rooms may be replaced by text messages for each individual pull station, smoke detector, or other type of initiating device. 

One of the common features of fire alarm systems of almost any age is the requirement for both primary and secondary power supply to ensure life safety even during a power failure. Since the majority of buildings with fire alarm systems do not have backup electrical generators, the secondary power supply will be from storage batteries contained within the fire alarm panel or in a separate enclosure nearby. The storage batteries are required to have the capacity to monitor this protected-premises system for at least 24 hours, plus five minutes sounding the alarms.

(2)

Photo 2 shows the same fire alarm control panel with the interior cover removed. 

  • 1 is the transformer for the primary power supply for the control panel and alarm system. The rectifier to convert alternating current (AC) to direct current (DC) is located on the main circuit board.
  • 2 is the battery for the secondary power supply. The battery charger is also located on the main circuit board.
  • 3 is the primary power indicator LED, showing that it is on.
  • 4 is the audible trouble indicator (electronic buzzer).
Another common feature of fire alarm systems is the need for regular maintenance and testing to ensure that they are reliable and functioning properly. In addition to the requirements for smoke and heat detectors detailed in the 2010 edition of National Fire Protection Association (NFPA) 72, National Fire Alarm and Signaling Code, there are requirements in Chapter 14 for testing and replacing storage batteries used for the secondary power supply. Testing of storage battery capacity is required annually and more frequently for some occupancies. Batteries are to be replaced according to the alarm system manufacturer’s instructions, which may vary by the type and size of alarm system and by the type of battery used. Common battery replacement intervals are three and five years.
 
The responsibility of the fire inspector or fire department company officer inspecting a building with a fire alarm system is to check the documentation provided by the building owner, occupant, or manager to verify that the required periodic testing and maintenance have been performed by a qualified person. This qualified person may be an employee of an alarm service contractor or an employee of the owner, occupant, or building manager.
 
The recordkeeping requirements for fire alarm systems are in the 2010 edition of NFPA 72, Article 14.6.2.
 
Download a PDF version of this article HERE.
 

Gregory Havel is a member of the Town of Burlington (WI) Fire Department; a retired deputy chief and training officer; and a 30-year veteran of the fire service. He is a Wisconsin-certified fire instructor II and fire officer II, an adjunct instructor in fire service programs at Gateway Technical College, and safety director for Scherrer Construction Co., Inc. Havel has a bachelor’s degree from St. Norbert College; has more than 30 years of experience in facilities management and building construction; and has presented classes at FDIC. 


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