Calculating the Battery Requirements Power Supply Calculations
NFS-640 Installation Manual P/N 51332:B1 12/01/2003 73
A.3 Calculating the Battery Requirements
A.3.1 Calculating the Battery Capacity
Use this table to determine the battery capacity needed for the system:
The following notes apply to Table 14:
1. NFPA 72-1999 Local, Proprietary, and Central Station systems requires 24 hours of standby
power followed by 5 minutes in alarm.
2. NFPA 72-1999 Auxiliary and Remote Station Systems require 60 hours or standby power
followed by 5 minutes in alarm.
3. Batteries installed in a system powered by an automatic starting engine generator need to
provide at least 4 hours of standby power.
4. Factory Mutual requires 90 hours of standby for deluge-preaction systems.
5. Emergency voice/alarm communications systems require 2 hours of operation in the alarm
condition. Due to the sporadic nature of voice operation, however, NFPA 72-1999 permits 15
minutes of operation at a maximum connected load to equal 2 hours of normal use.
6. If the total exceeds 25 AH, the system requires a separate NFS-LBB battery enclosure for two
PS-12550, 55 AH batteries in a separate NFS-LBB enclosure. If the total exceeds 55 AH, the
system requires an auxiliary battery charger with sufficient amp-hour capacity; this charger
must be UL-listed for Fire-Protective Signaling. If CHG-120 battery charger is used, it requires
a second NFS-LBB enclosure.
7. The following battery derating factors must be used for Canadian installations using NFS-640
charger:
• For a 12 AH battery, use derating factor of 1.2
• For a 25 AH battery, use derating factor of 1.5
• For a 55 AH battery, use derating factor of 1.8
Table 14 Secondary Power Standby and Fire Alarm Load
Current (amps) X Time (hours) = AH
Secondary Non-Fire
Alarm Current (from
column 3 in Table 12)
________________ X
Required Secondary Non-Fire
Alarm Standby Time (24 or 60
hours)
________________ = _________AH
APS-6R
Standby Load
Current
________________
X
Required Secondary Non-Fire
Alarm Standby Time (24 or 60
hours)
________________ = _________AH
Secondary Fire
Alarm Load (from
Table 13)
________________
X
Required Fire Alarm Standby
Time: (for 5 minutes, enter
0.084; for 15 minutes, enter
0.25)
________________
= _________AH
Sum Column for Total Secondary Amp Hours calculated = _________AH
Multiply by the derating factor x 1.2 (see Note 7) = _________AH
Battery Size – Total Secondary Amp Hours Required = _________AH
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