NFPA Journal - Summer 2021 - 49

Fire alarm systems must remain reliable
when emergency power supplies are in
use, such as these backup generators.
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measuring the temperature to ensure
that the battery is not 18° F (10° C)
above ambient temperature; measuring the voltage to ensure the battery and
charger are still operational; measuring
the voltage at each cell of the battery to
confirm each cell is greater than 13.26
volts; and measuring the internal ohmic
value of each battery and comparing it to previous tests to ensure that
the battery does not have 30 percent
or more conductance or 40 percent or
more resistance or impedance than
previous tests, or that it is outside the
manufacturer's acceptable ranges.
Every three years the batteries need to
either be replaced, or a load test needs to
be conducted. Load tests are conducted
by putting a known load (which can
be obtained from the battery manufacturer) on the battery for a given time.
The battery is discharged until it reaches
its end voltage. Based on the known load

and the time taken to discharge, you can
then calculate the capacity of the battery
and apply any adjustments for temperature. The battery must be replaced if the
capacity is less than 80 percent of its
rated capacity.
All of these ITM requirements focus
on the batteries themselves, but there
are additional tests that need to be
completed to make sure the entire
system will operate under secondary
power. First, if the system is supplied
by an emergency generator, power will
need to be transferred to the generator monthly to ensure that the transfer
switch and generator will be able to
supply the fire alarm. Additionally, all
primary power to the system needs
to be disconnected annually so the
required standby and alarm current
to the system can be measured and
compared to the available battery
capacity. It is important to remember

that these batteries need to be able
to provide the 24-hour standby and 5
(or 15) minutes of alarm, or 4 hours of
standby if there is also an emergency
generator. Finally, the system needs to
be operated under secondary power
in alarm for at least 5 or 15 minutes
depending on the system type.
We rely on the fire alarm system as a
key component of the fire and life safety
of our buildings, and we rely on the
secondary power supply to keep the fire
alarm system operational in the event of
a power outage. It is important that you
understand and follow the ITM requirements in NFPA 72 to ensure that the fire
alarm system remains reliable with the
secondary power supply.
Shawn Mahoney, P.E., is a technical services
engineer at NFPA. NFPA members and AHJs can
use the Technical Questions tab to post queries on
NFPA 72 at nfpa.org/72. To follow the progress
on the upcoming edition of the code, visit
nfpa.org/72next.

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