42 Remote Booster Power Supply Technical Reference Manual
Where:
Rmax = maximum resistance
Rw = wire resistance factor
Example: You’re using regulated notification appliances. Assume that the
maximum operating current for each appliance is 100 mA for DC power, and that
20 appliances will be placed on the NAC. The cable is 12 AWG wire, and the
manufacturer specifies a wire resistance factor of 0.002 /ft.
Itot = Ia
= 20 × 0.1 A
= 2 A
Vm = Vr (Itot × K)
= 19.1 V (2 A × 0.59 V/A)
= 19.1 V 0.76 V
= 18.94 V
Vd = Vm Va
= 18.94 V 16.0 V
= 2.94 V
Rmax = Vd / Itot
= 2.94 V / 2.0 A
= 1.47
Lc = (Rmax / Rw) / 2
= (1.47 / 0.002 /ft) / 2
= (367.5 ft) / 2
= 367.5 ft
So the maximum wire run for this NAC would be 367.5 ft (rounding down for
safety).
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