Figure 7: Maximum wire length for low-voltage
Inputs and Outputs by current and wire size
Communication bus and supply power
wiring guidelines
Communications bus and supply power terminal
blocks, ratings, and requirements provides
information about the functions, ratings, and
requirements for the communication bus and
supply power terminals; and guidelines for wire
sizes, cable types, and cable lengths when wiring
the communication buses and 24 VAC supply power.
In addition, observe these guidelines when wiring
an SA or FC bus and 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 required 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.
Communications bus and supply power terminal blocks, ratings, and requirements
Table 4: Communications bus and supply power terminal blocks, functions, ratings, requirements, and
cables
Terminal block/Port
label
Terminal labels Function, electrical ratings/Requirements required cable type
+
-
FC or SA Bus Communications
COM
Signal Reference (Common) for FC or SA Bus
communications
FC BUS
or
SA BUS
SHLD
or
SA PWR
SHLD on FC Bus: Isolated terminal (optional
shield drain connection)
SA PWR on SA Bus: 15 VDC power lead
connection.
Note: The SA PWR terminal on an IOM
expansion module does not supply 15
VDC. The SA bus supervisor supplies 15
VDC to devices on the SA bus requiring
power.
FC Bus: 0.6 mm (22 AWG) stranded, 3-wire
twisted, shielded cable required.
SA Bus: 0.6 mm (22 AWG) stranded, 4-wire
(2 twisted-pairs), shielded cable required.
Note: On the SA Bus, the + and - wire
are one twisted pair, and the COM
and SA PWR are the second twisted
pair of wires.
SA/FC BUS
(Port)
RJ-12 6-Position Modular Connector provides:
FC or SA Bus Communications
FC or SA Bus Signal Reference and 15 VDC
Common
Commissioning Converter or ZFR /ZFR Pro
Wireless Router
(Maximum total current draw for SA Bus is 100
mA.)
Wireless Commissioning Converter
retractable cable or 24 AWG 3-pair CAT 3
Cable <30.5 m (100 ft)
HOT
24 VAC Power Supply - Hot
Supplies 20–30 VAC (Nominal 24 VAC)
24~
COM 24 VAC Power Supply - Common
0.8 mm to 1.0 mm
(18 AWG) 2-wire
IOM3733 Input/Output Module Installation Guide8