Edwards Signaling eFSA250 - Manual (Page 227)

Appendix B: Worksheets
E-FSA64 and E-FSA250 Technical Reference Manual 215
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 eFSA64 panel = 0.20 V/A