Appendix B: Worksheets
194 P/N 3102351-EN • REV 005 • ISS 28DEC18
Notification appliance circuit calculations worksheet
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 are 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
Other, more detailed methods that distribute the appliance load along the NAC cable may
indicate that longer cable runs are possible.
What you’ll need
Appliance and cable values
Whether you use the worksheet method or the equation method, you’ll need to know:
• The minimum operating voltage required for the appliances
• The maximum operating current drawn by each appliance
• The resistance per unit length of the wire used (Ω/ft.)
This information can be found on the appliance installation sheets and on the cable
specification sheet.
Power supply values
For either method, you’ll need some fixed or calculated operating values for your specific
power supply. The fixed values are:
• Source voltage = 20.4 V
• Load factor for VS1 panel = 0.20 V/A
• Load factor for VS4 panel = 0.24 V/A
• Power type = FWR
The source voltage is the theoretical operating minimum for the power supply, and is
calculated as 85% of 24 volts.
The load factor is a measure of how the power supply voltage reacts when a load is applied.
The load factor measures the voltage drop per ampere of current drawn by the load.
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