Edwards Signaling FSC Series - Manual (Page 82)

Appendix A: System calculations
74 FSC Series Technical Reference Manual
NAC 4 voltage drop calculations
Circuit
length
Total
current [1]
Wire resistance
per 1000 ft [2]
Voltage
drop
Panel
voltage [3]
Voltage
drop
End of line
voltage [4]
Voltage
drop
Panel
voltage
[4]
% of
voltage
drop
V  V = V V  V =
Notes
[1] Use the operating current ratings found on the installation or catalog sheet of
each device.
[2] Use 3.5 Ω for 12 AWG and 2.5 sq mm wire, 5.2 Ω for 14 AWG and 1.5 sq mm
wire, 8.0 Ω for 16 AWG and 1.0 sq mm wire, and 13.0 Ω for 18 AWG and
0.75 sq mm wire.
[3] Use 19.5 V for three-zone panels, 19.5 V for five-zone panels, and 19.4 V for
ten-zone panels.
[4] This voltage cannot drop below 16 VDC.
Notification appliance circuit calculations
Introduction
This topic shows you how to determine the maximum cable length of a
notification appliance circuit (NAC) for a given number of appliances.
Two methods are presented: worksheet and equation. The worksheet method is
simpler, but your installation must meet the criteria listed on the worksheet. If
your installation does not meet these criteria, you need to use the equation
method.
The methods given here determine cable lengths that work under all operating
conditions. The calculations ensure that the required operating voltage and
current will be supplied to all notification appliances. To do this, we assume these
two worst-case conditions:
• The voltage at the NAC terminals is the minimum provided by the power
supply.
• The notification appliances are clustered at the end of the NAC cable.