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D9112 Operation & Installation Manual
Page 68
74-06144-000-C 2/96
© 1993-1996 Radionics
Standby Battery Calculation for
NFPA 72 Fire Alarm Applications
Current Chart First
See the
D9112 Standby Battery and Current Rating Chart
for totals B and C used in the
formulas below. When connecting two batteries, use either the D122 Dual Battery Wiring
Harness or the D8132 Battery Charger Module.
The D8109 enclosure is required for all commercial fire applications.
The D8108A enclosure is required for fire/burglary applications with a local bell.
Central Station or Local Systems
Central Station or Local Systems require 24 hours of standby plus 5 minutes of alarm operation
at the end of the 24 hour period. A single battery is sometimes adequate for Central Station
Systems, but you must install two batteries to meet the basic standby requirements for a
Local System installation. You must use battery ampere hour (Ah) calculations to verify
compliance. The following formula includes the calculation for 5 minutes of alarm operation
at the end of the 24 hour period, as well as a 10% contingency factor which allows for
depletion of battery capacity with age.
Central Stations or Local Systems Ampere-Hour Calculation Formula
Total B Hours Total C Hours Contingency Total Ah
( ________ x 24 ) + ( _______ x .083 ) + 10% = __________
Total Ah requirements must not exceed Ah capacity of batteries:
Two D126 Batteries = 14 Ah