Edwards Signaling eFSA250 - Manual (Page 230)

Appendix B: Worksheets
218 E-FSA64 and E-FSA250 Technical Reference Manual
Equation method
Appliance operating voltage and current
Regulated notification appliances have an operating range from 16 V to 33 V.
Use 16 V as the minimum appliance voltage when using regulated notification
appliances.
When using special application 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 is 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 of appliances
of that type.
Wire resistance
Typical wire resistances are shown in the following table.
Table 46: Typical wire resistances
Wire
gauge
Resistance
1-strand uncoated copper
Resistance
7-strand uncoated copper
Ω per foot Ω per meter Ω per foot Ω per meter
12 AWG 0.00193 0.00633 0.00198 0.00649
14 AWG 0.00307 0.01007 0.00314 0.01030
16 AWG 0.00489 0.01604 0.00499 0.01637
18 AWG 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
1. Calculate the total current (Itot) as the sum of the maximum operating
currents for all the appliances.
Itot = ΣIa