Appendix B: Worksheets
EST iO64 and iO500 Technical Reference Manual
213
Itot =
Σ
Ia
Where:
Ia = appliance maximum current
See 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
64 point panel:
For the power supply, Vs is 20.4 V and K is 0.20 V/A.
250/500 point 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
