Edwards Signaling FSC Series - Manual (Page 88)

Appendix A: System calculations
80 FSC Series Technical Reference Manual
Itot = ΣIa
= 20 × 0.1 A
= 2 A
Vm = Vr − (Itot × K)
= 20.4 V − (2 A × 0.20 V/A)
= 20.4 V − 0.4 V
= 20.0 V
Vd = Vm − Va
= 20.0 V − 16.0 V
= 4.0 V
Rmax = Vd / Itot
= 4.0 V / 2.0 A
= 2.0 Ω
Lc = (Rmax / Rw) / 2
=
(2.0 Ω / 0.002 Ω/ft) / 2
= 1000 ft / 2
= 500 ft
So the maximum wire run for this NAC would be 500 ft (rounding down for
safety).