NFS-640 Installation Manual P/N 51332:B1 12/01/2003 69
Appendix A Power Supply Calculations
Calculations must be done to determine standby and alarm DC current loads. Ampere-hour
requirements must be calculated as well to determine battery size.
The on-board power supply provides filtered 24VDC power that may be used for operating external
devices. Use Table 12 to determine if external loading is within the capabilities of the power supply.
A.1 Calculating AC Branch Circuit Current
Use the table below to determine the total amount of current, in AC amperes, that a 120 VAC, 50/60 Hz
service must be able to supply to the fire alarm system. Devices rated for 240 VAC operation will draw
approximately one-half the current listed in Table 11.
AC Branch Circuit Installation
For guidelines on wiring the AC branch circuit current, see “Operating Power: AC Branch Circuit” on
page 77 in Appendix B.1 “Electrical Specifications”.
A.2 Calculating the System Current Draws
The control panel’s main power supply must be able to power all internal system devices (and several
types of external devices) continuously during non-fire alarm conditions. Use column 1 in Table 12 to
calculate the Non-Fire Alarm Load on the power supply regulator when applying primary power. The
main power supply must also provide a finite amount of additional current during a fire alarm condition.
Use column 2 in Table 12 to calculate the additional current needed during fire alarms. The
requirements for non-fire alarm and fire alarm current loads cannot exceed the capabilities of the power
supply as listed below:
• 3 A at 24 VDC during Standby; and
• 6 A at 24 VDC during Alarm.
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
Table 11 120 VAC Fire Alarm Circuit
Device Type
No. of
Devices
Current
(amps)
Total
Current
Main Power Supply [ 1 ] X 3.0 = 3.0
AA-30 [ ] X 1.00 =
AA-120 [ ] X 1.85 =
ACPS-2406 [ ] X
2.7
1
1. Separate calculations are required for any devices powered by the ACPS-2406. It has its own
integral battery charger and batteries can be connected directly to it. Refer to the ACPS-2406
Installation Manual for its battery calculations.
=
APS-6R [ ] X 2.5 =
CHG-120 [ ] X 2.0 =
Sum column for AC Branch Current required=amps
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