Edwards Signaling EBPS Remote Booster Power Supply - Manual (Page 47)

Remote Booster Power Supply Technical Reference Manual 41
Calculating cable length
To calculate the maximum NAC cable length:
1. Calculate the total current (Itot) as the sum of the maximum operating
currents for all the appliances.
Itot = ΣIa
Where:
Ia = appliance maximum current
See the appliance installation sheets for Ia. Remember to use the maximum
operating current specified for DC power.
2. Calculate the minimum voltage (Vm).
Vm = Vs − (Itot × K)
Where:
Vs = source voltage
Itot = total current (from above)
K = load factor
For the power supply, Vs is 19.1 V and K is 0.59 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
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