NFS2-640/E Installation Manual —
P/N 52741:P2 7/10/14
65
Calculating the System Current Draws
Power Supply Calculations
How to Use the Calculating Tables
As used in this section, “Primary” refers to the control panel’s on-board power supply, its primary
source of AC power. “Secondary” refers to the control panel’s backup batteries (or any other 24
VDC power supply listed for Fire Protective Signaling and connected in place of the batteries). The
term “standby” refers to the output current required when no fire alarm is present. The term “alarm”
refers to the output current required when a fire alarm is present.
The Primary Power Source Non-Alarm Current and Alarm Current columns are DC current
calculations. These calculations confirm that the power supply can provide enough current to
support the system during Primary Non-Fire Alarm and Fire Alarm conditions.
Quantities
List the number of devices powered by the FACP and its power supply. Devices
powered by the Accessories Output (TB10 and TB2) draw current directly from the panel. Devices
powered by the Panel Output draw current through the fire panel’s connection to the power supply.
Use these quantities to calculate total current draw of each set of devices in calculation columns 1,
2, and 3.
Calculation Column 1 (Primary, Non-Fire Alarm Current in amps)
Add the contents of
calculation column 1 to get the current drawn from the power supply during a non-alarm condition,
with AC power applied. This current draw cannot exceed 4.4 A without an auxiliary power supply.
Calculation Column 2 (Primary, Fire Alarm Current in amps)
Calculation column 2 lets
the system designer determine the current load that the power supply must support during a fire
alarm. The total current draw during a fire alarm cannot exceed 6 A without an auxiliary power
supply.
Typically, a system should contain capacity to activate all output circuits and relays, and support
fire alarms on no less than 10% of Initiating Device Circuits, subject to the requirements of the
Authority Having Jurisdiction (AHJ).
The Control Panel provides power for Notification Appliance Circuits. Refer to the Device
Compatibility Document for 24 VDC notification appliances that are UL- and ULC-listed for fire
alarm systems.
Calculation Column 3 [Secondary (Battery) Non-Alarm Current]
Column 3 lets the
system designer calculate the non-fire alarm current drawn from the secondary source in a non-fire
alarm condition during AC power loss.The non-fire alarm current is required to complete the
standby battery calculations. After summing all current draws, insert the total in Table A.3.
