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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 CPS-24/E power supply provides filtered 24VDC power that may be used for operating
external devices. Use Table A.2 to determine if external loading is within the capabilities of the
power supply.
A.1 Calculating AC Branch Circuit Current
Use Table A.1 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 220-240 VAC
operation will draw approximately one-half the current listed in Table A.1.
Device Type
CPS-24 Power Supply
CPS-24/E Power Supply
FCPS-24S6/S8
ACPS-2406
ACPS-610
ACPS-610/E
APS-6R
CHG-120
Sum column for AC Branch Current required=amps
* Separate calculations are required for any devices powered by the ACPS-
610 or ACPS-2406. They have their own integral battery charger and
batteries can be connected directly to them. Refer to the ACPS-2406 or
ACPS-610 Installation Manuals for battery calculations.
AC Branch Circuit Installation
For guidelines on wiring the AC branch circuit current, see "Operating Power: AC Branch Circuit"
on page 60 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 A.2 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 A.2 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:
•
3.9 A at 24 VDC during Standby; and
•
7.4 A at 24 VDC during Alarm.
The current draw from all NACs plus DC output from TB10 and TB2 is 3.0 A during standby, and
6.0 A in alarm.
52
No. of Devices
[ 1 ]
X
[
]
X
[
]
X
[
]
X
[
]
X
[
]
X
[
]
X
[
]
X
Table A.1 120 VAC Fire Alarm Circuit
NFS-320/E/C Installation Manual — P/N 52745:M2 7/1/14
Current (amps)
Total Current
5.0
=
5.0
2.5
=
3.2
=
*
2.7
=
*
5.0
=
*
2.5
=
2.5
=
2.0
=
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