Johnson Controls IOM2721 Installation Manual page 7

Cable and wire length guidelines
The following table defines cable length guidelines for the various wire sizes that may be used for wiring low-voltage
(<30 V) input and outputs.
Table 3: Cable length guidelines
Guideline Wire size/gauge and type
1.0 mm (18 AWG) stranded copper
0.8 mm (20 AWG) stranded copper
A
0.6 mm (22 AWG) stranded copper
0.5 mm (24 AWG) stranded copper
1.0 mm (18 AWG) stranded copper
0.8 mm (20 AWG) stranded copper
B
0.6 mm (22 AWG) stranded copper
0.5 mm (24 AWG) stranded copper
See Figure 8 to select wire size/gauge.
C
Use stranded copper wire.
Maximum cable length versus load current
Use the following figure to estimate the maximum cable
length relative to the wire size and the load current (in
mA) when wiring inputs and outputs.
Note: The following information applies to low-
voltage (<30 V) inputs and outputs only.
Figure 8: Maximum wire length for low-voltage (<30 V)
Inputs and Outputs by current and wire size
Maximum cable length
and type
457 m (1,500 ft) twisted wire
297 m (975 ft) twisted wire
183 m (600 ft) twisted wire
107 m (350 ft) twisted wire
229 m (750 ft) twisted wire
137 m (450 ft) twisted wire
91 m (300 ft) twisted wire
61 m (200 ft) twisted wire
See Figure 8 to determine
cable length. Use twisted
wire cable.
Communications bus and supply power
wiring guidelines
Table 4 provides information about the functions, ratings,
and requirements for the communication bus and supply
power terminals; it additionally provides guidelines for
wire sizes, cable types, and cable lengths when wiring the
expansion module's communication buses and supply
power.
In addition to the guidelines in Table 4, observe these
guidelines when wiring an SA or FC bus and the 24 VAC
supply power:
• Run all low-voltage wiring and cables separate from
high-voltage wiring.
• All SA and FC bus cables, regardless of wire size, should
be twisted, insulated, stranded copper wire.
• Shielded cable is strongly recommended for all SA and
FC bus cables.
• Refer to the MS/TP Communications Bus Technical
Bulletin (LIT-12011034) for detailed information
regarding wire size and cable length requirements for
the SA and FC buses.
IOM2721 Input/Output Module Installation Guide
Assumptions
100 mV maximum voltage drop
Depending on cable and the connected input or
output device, you may have to define an offset
in the setup software for the input or output
point.
100 mV maximum voltage drop
Depending on cable and the connected input or
output device, you may have to define an offset
in the setup software for the input or output
point.
N/A
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