Appendix B: Worksheets
P/N 3102352-EN • REV 005 • ISS 28DEC18 191
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 48: Typical wire resistances
Resistance
1-strand uncoated copper
Resistance
7-strand uncoated copper
Ω per foot Ω per meter Ω per foot Ω per meter
0.00193 0.00633 0.00198 0.00649
0.00307 0.01007 0.00314 0.01030
0.00489 0.01604 0.00499 0.01637
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
Where:
Σ = sum of all
Ia = appliance maximum current
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