System calculations
EST3 Installation and Service Manual B.11
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
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:
• Maximum voltage = 27.4 V
• Rated voltage = 20.4 V
• Load factor = 0.37 V/A
• Power type = DC
To Next Page
Loading...
Need help?
General