Edwards Signaling FSC Series - Manual (Page 86)

Appendix A: System calculations
78 FSC Series Technical Reference Manual
When using unregulated notification appliances, refer to the installation sheets to
determine the minimum appliance voltage required.
What if there are different types of appliances in the NAC, and each type has a
different minimum operating voltage? In this case, use the highest minimum
voltage required by any appliance.
The total current requirement for the appliances will be the sum of the individual
maximum currents drawn by each appliance when using FWR power. Use the
maximum current for the appliance over the 16 V to 33 V range.
If all appliances draw the same maximum current, the total current is the
maximum current multiplied by the number of appliances. If different appliance
types have different maximum currents, the total current is the sum of the
maximum current for each appliance type multiplied by the number appliances of
that type.
Wire resistance
Typical wire resistances are shown in the following table.
Table 26: Typical wire resistances
Wire
gauge
(AWG) Resistance
1 strand uncoated copper Resistance
7 strand uncoated copper
Ω per foot Ω per meter Ω per foot Ω per meter
12 0.00193 0.00633 0.00198 0.00649
14 0.00307 0.01007 0.00314 0.01030
16 0.00489 0.01604 0.00499 0.01637
18 0.00777 0.02549 0.00795 0.02608
When performing these calculations, always refer to the actual cable supplier
documentation and use the actual Ω/ft (or Ω/m) for the cable being used.
Calculating cable length
To calculate the maximum NAC cable length:
1. Calculate the total current (Itot) as the sum of the maximum operating
currents for all the appliances.
Itot = ΣIa
Where:
Ia = appliance maximum current