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Power Supply Calculations
7.4 Calculating the Battery Size
Use Table 7.4 to calculate the total Standby and Alarm load in ampere hours (AH). This total load
determines the battery size (in AH), required to support the control panel under the loss of AC
power. Complete Table 7.4 as follows:
1. Enter the totals from Table 7.3 on page 181, Calculation Columns 2 and 3 where shown
2. Enter the NFPA Standby and Alarm times (refer to 'NFPA Requirements' below)
3. Calculate the ampere hours for Standby and Alarm, then sum the Standby and Alarm ampere
hours
4. Multiply the sum by the derating factor of 1.2 to calculate the proper battery size (in AH)
5. Write the ampere hour requirements on the Protected Premises label located inside the
cabinet door
Secondary Standby Load
(total from Table 7.3 Calculation
Column 3)
[
]
Primary Alarm Load
(total from Table 7.3 Calculation
Column 2)
[
]
Sum of Standby and Alarm Ampere Hours
Multiply by the Derating Factor
Battery Size, Total Ampere Hours Required
7.4.1 NFPA Battery Requirements
•
NFPA 72 Local and Proprietary Fire Alarm Systems require 24 hours of standby power
followed by 5 minutes in alarm
•
NFPA 72 Central, Auxiliary and Remote Station Fire Alarm Systems require 60 hours of
standby followed by 5 minutes in alarm. Batteries installed in a system powered by a
generator need to provide at least 4 hours of standby power
7.4.2 Selecting and Locating Batteries
Select batteries that meet or exceed the total ampere hours calculated in Table 7.4 . The control
panel can charge batteries in the 7 AH to 18 AH range. The control panel cabinet is capable of
housing batteries up to 18 AH. Batteries larger than 18 AH require a UL listed external battery
charger and cabinet such as the BB-26, BB-55F or other UL listed external battery cabinet.
182
Table 7.4 Total Secondary Power Requirements at 24 VDC
Required Standby Time
(24 hours)
X[
Required Alarm Time
(for 5 min., enter 0.084,
for 10 min., enter 0.168)
X[
]
=
=
]
=
X 1.2
=
AH
AH
AH
AH
MS-9050UD PN 52413:C 01/23/08
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