Power Supply Requirements Calculating the Battery Size
44 HPFF8(E)/HPFF8CM(E) NAC Expander — P/N 53499:B4 10/1/2018
6.4 Calculating the Battery Size
Use Table 6.5 to calculate the total Standby and Alarm load in amperes hours (AH). This total load determines the battery size (in AH)
required to support the power supply under the loss of AC. Complete Table 6.5 as follows:
1. Enter the totals from Table 6.4, Calculation Columns 2 and 3 where shown.
2. Enter the NFPA Standby and Alarm times. Refer to “NFPA Battery Requirements.”
3. Calculate the ampere hours for Standby and Alarm conditions, 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.
6.4.1 NFPA Battery Requirements
NFPA 72 Local and Propriety Fire Alarm Systems require 24 hours of standby power followed by 5 minutes in alarm
6.4.2 Selecting and Locating Batteries
Select batteries that meet or exceed the total ampere hours calculated in Table 6.5. The power supply can charge 7 AH to 26 AH batter-
ies.
The standard HPFF wall cabinet is capable of housing batteries up to 18 AH. Larger capacity batteries can be used if they are housed in
an external UL-Listed enclosure, along with a UL-Listed battery charger with sufficient capacity to restore the full charge to the batteries
in the required time. To use an external battery charger, remove the control board’s jumper at J1 CHARGER DISABLE and connect an
external battery to the battery terminals on the control PCB. The alternate enclosure and battery charger shall be listed for Fire Protective
Signaling use.
The HPFF8CM is a chassis mount (CM) model that can fit two 12AH batteries. It is used for a multi-pack option that allows up to four
HPFF8 units mounted in large equipment enclosures.
6.5 NAC Circuit Loop Wiring Requirements
Make sure these requirements are met:
1. For any NAC circuit with a full load (up to 3 Amps), the total wire resistance must be less than or equal to 0.66 Ohms.
and
2. The NAC loop current draw multiplied by total wire resistance on any single NAC circuit cannot exceed 2.0 volts.
Secondary Standby Load
(total from Table 6.4 Calculation
Column 3)
[ ]
Required Standby Time
(24 or 60 hours)
X [ ] = AH
Primary Alarm Load
(total from Table 6.4 Calculation
Column 2)
[ ]
Required Alarm Time
(for 5 min., enter 0.084,
for 10 min., enter 0.168)
X [ ] = AH
Sum of Standby and Alarm Ampere Hours = AH
Multiply by the Derating Factor X 1.2
Battery Size, Total Ampere Hours Required = AH
Table 6.5 Total Secondary Power Requirements at 24 VDC
NOTE: The HPFF8 cannot be mounted in the top position of the large equipment enclosure.
NOTE: For loads smaller than 3 Amps, use the second calculation.
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