Appendix B: Worksheets
Vigilant VS1 and VS2 Technical Reference Manual
211
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 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
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
