Edwards Signaling FSC Series - Manual (Page 83)

Appendix A: System calculations
FSC Series Technical Reference Manual 75
Other, more detailed methods that distribute the appliance load along the NAC
cable may indicate longer cable runs.
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 = 0.25 A/V for three-zone panels, 0.40A/V for five-zone panels,
and 0.20 A/V for ten-zone panels
• 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.
The power type reflects the type of power supplied to the NAC terminals at
minimum voltage. The current draw of notification appliances can vary
substantially with the type of power supplied: full-wave rectified (VFWR) or direct
current (VDC). It is important to know the power type at minimum terminal
voltage.
You’ll need to calculate the following values relating to your power supply and to
the NAC circuit current. These are:
• Minimum voltage
• Voltage drop