Control Panel Description and Installation
150964 4-17
4.13.3 Number of SBUS Devices
The table below shows the maximum number of devices and maximum distance from the
4821/4820 for SBUS devices, assuming a maximum of 2 volts of line drop and 100 mA of
current per device. Following these guidelines guarantees that there will be sufficient voltage
in the worst case (when the battery voltage is 10V or greater and when all devices are located
at the end of the wiring). (The formula used to generate this table is shown in the note below.)
Note: The following formula was used to calculate the maximum wire distances:
Max. Distance = 500V
NIRpu
Table 4-5: Number of SBUS Devices
Model 4821/4820 to SBUS Devices
Maximum wiring distance with 14 - 22 gauge wire (AWG)
Num. of Devices
per 4-Conductor Wire 22 Gauge 18 Gauge 16 Gauge 14 Gauge
1 617 ft. 1562 ft. 2487 ft. 3937 ft.
Max. distance for all
home-run devices.
2 308 ft. 781 ft. 1243 ft. 1968 ft.
Max. distance for 2 T-
tapped or daisy-chained
devices.
3 205 ft. 520 ft. 829 ft. 1312 ft.
Max. distance for 3 T-
tapped or daisy-chained
devices.
4 154 ft. 390 ft. 621 ft. 904 ft.
Max. distance for 4 T-
tapped or daisy-chained
devices.
where: V = 2 volts (Maximum allowed voltage drop under low battery condition of 10.0
volts.)
N = Number of devices
I = .1 amps (Worst case current draw for all devices.)
Rpu = Ohms per 1,000 feet for various wire gauges, see below.
Wire gauge
Ohms per 1,000 feet
22
16.2
Ω
18
6.4
Ω
16
4.02
Ω
14
2.54
Ω
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