Edwards Signaling eFSA250 - Manual (Page 231)

Appendix B: Worksheets
E-FSA64 and E-FSA250 Technical Reference Manual 219
Where:
Σ = sum of all
Ia = appliance maximum current
Refer to the appliance installation sheets for Ia. Remember to use the
maximum operating current specified for FWR power.
2. Calculate the minimum voltage (Vm).
Vm = Vs − (Itot × K)
Where:
Vs = source voltage
Itot = total current (from above)
K = load factor
eFSA64 panel: For the power supply, Vs is 20.4 V
and K is 0.20 V/A.
eFSA250 panel: For the power supply, Vs is 20.4 V and K is 0.24 V/A
3. Calculate the allowable voltage drop (Vd) between the power supply and the
appliances.
Vd = Vm − Va
Where:
Vm = minimum voltage (from above)
Va = appliance minimum voltage
For regulated notification appliances, Va is 16 V. For special application
notification appliances, Va is the lowest operating voltage specified on the
appliance installation sheet.
4. Calculate the maximum resistance (Rmax) for the wire.
Rmax = Vd / Itot
Where:
Vd = voltage drop
Itot = total current
5. Calculate the maximum length of the cable (Lc), based on the maximum
resistance allowed, the resistance of the wire, and the number of wires in the
cable (two).
Lc = (Rmax / Rw) / 2
Where:
Rmax = maximum resistance
Rw = wire resistance factor