Power Supply Calculations Calculating the System Current Draws
72 NFS-640 Installation Manual P/N 51332:B1 12/01/2003
A.2.1 Calculating the Maximum Secondary Power Fire
Alarm Current Draw
Use the table below to determine the maximum current requirements of secondary power source
during fire alarm conditions. The result obtained is the amount of current that the batteries must be
able to supply to the fire alarm system. Use the result in Table 14 to determine the size of the
batteries needed for the fire alarm system.
Results taken from the table below assume that, while in a fire alarm condition, batteries must feed
the main power supply (and any additional supplies such as the APS-6R and AA-30) with the
maximum rated power each supply can provide.
Note: The Secondary Fire Alarm Load cannot exceed the following:
• 9 A with PS-12120 batteries.
• 12 A with PS-12250 batteries.
• 20 A with PS-12550 batteries.
Contact rating (maximum current) for battery-switching relay in the control panel
Table 13 Maximum Secondary Power Fire Alarm Current Draw
Device Quantity
Current
(in amps)
Total Current/
Type
Alarm Current, from Table 12, col 2 =
APS-6R
1
1. Actual load current may be used in place of maximum rated supply current. To
calculate actual load current, sum the current draws for each appliance connected to
APS-6R supplies.
[] X 6 =
AA-30
2
2. Exclude Amplifiers that are employed for backup.
[] X 3 =
AA-120
2
[ ] X 7.3 =
Sum Column for Secondary Fire Alarm Load =
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