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
Total B | Hours | Total C | Hours | Contingency | Total Ah | |
( ________ | x 24 ) | + | ( _______ x | .083 ) + | 10% | = __________ |
Total Ah requirements must not exceed Ah capacity of batteries: |
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Two D126 Batteries = | 14 Ah |
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| D9112 Operation & Installation Manual |
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