Power Supply Calculations Calculating the Battery Requirements
74 NFS-640 Installation Manual P/N 51332:B1 12/01/2003
When batteries are charged by CHG-120 charger use a derating factor of 1.2 for 25 AH and 55
AH batteries.
A.3.2 Calculating the Battery Size
Use this table to choose the battery size, in amp-hours, needed to support the fire alarm system.
Select batteries that meet or exceed the Total Amp-Hours calculated in Table 14 and that are within
the acceptable battery charger range (12-55 AH). Write the amp-hours requirements on the
Protected Premises label.
Table 15 Selecting the Battery Size
Battery
Size
Voltage
Rating
Number
Required
Part
Number Backbox Size
12 AH 12 volts two PS-12120 SBB-A4*, SBB-B4*,
SBB-C4*, SBB-D4*
25 AH 12 volts two PS-12250 SBB-A4*, SBB-B4*,
SBB-C4*, SBB-D4*
55 AH 12 volts two PS-12550 NFS-LBB*
* Red version available; add “R” to part number listed here
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