FireLite SLC Wiring Manual — P/N 51309:R3 7/29/2019
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Appendix A: Power Considerations
A.1 Supplying Power to 24 VDC Detectors and NACs
A.1.1 Resistance and Size
To determine the minimum resistance that can be tolerated in supplying power to 24 VDC 4-wire devices and NACs, use the calculation
below. Use this resistance to select the proper gauge wire for the power run from the manufacturer’s specifications for the desired wire.
For Four-Wire Detectors:
For NACs:
Where:
Rmax = maximum resistance of the 24 VDC wires
Vms = minimum supply voltage
Vom = minimum operating voltage of the detector or end-of-line relay, whichever is greater, in volts
N = total number of detectors on the 24 VDC supply circuit
Is = detector current in standby
Na = number of detectors on the 24 VDC power circuit which must function at the same time in alarm
Ia = detector current in alarm
Ir = end-of-line relay current
Nb = number of Notification Appliance Devices
Ib = Notification Appliance current when activated
The minimum supply voltages produced by Fire•Lite power supplies are listed below:
Rmax =
(Vms - Vom)
(N)(Is) + (Na)(Ia) + (Ir)
Rmax =
(Vms - Vom)
(Nb)(Ib)
NOTE: This simplified equation assumes that the devices are at the end of a long wire run.
FACP Vms Power Supply Vms
MS-9200 16.0 FCPS-24F 19.1
MS-9600 16.0 FCPS-24FS6/FCPS-24FS8 19.1
MS-9200UD/MS-9200UDLS 19.05
MS-9050UD 18.75
ES-50X 19.2
ES-200X 19.2
Table A.1 Minimum Supply Voltage
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