System calculations
EST3 Installation and Service Manual B.13
Worksheet method
Use this worksheet to determine the maximum cable length of a
notification appliance circuit for a given number of appliances.
Use this worksheet only if all the appliances are regulated. That
is, they must have a minimum operating voltage of 16 V.
Worksheet 1: NAC cable length
NAC1 NAC2 NAC3 NAC4
Total operating current [1]
A
Load factor
×
0.37 0.37 0.37 0.37 V/A
Load voltage drop
=
V
Rated voltage
20.4 20.4 20.4 20.4 V
Load voltage drop
−
V
Minimum voltage
=
V
Regulated appliance voltage
−
16.0 16.0 16.0 16.0 V
Voltage drop [2]
=
V
Total operating current
÷
A
Maximum resistance
=
Ω
Wire resistance (Ω/ft) [3]
÷
Maximum wire length
=
ft
÷
2 2 2 2
Maximum cable length
=
ft
[1] Total of the maximum operating currents for all appliances as specified for DC power. See
the appliance installation sheets for operating currents.
[2] This voltage drop is valid for regulated notification appliances only. For unregulated
appliances, see “Equation method,” later in this topic.
[3] Use the manufacturer’s published wire resistance expressed in ohms per foot. For typical
values, see Table 4, later in this topic.
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