Johnson Controls IOM3731-0A Installation Manual page 8

Figure 8: Maximum wire length for low-voltage
Inputs and Outputs by current and wire size
Communications bus and power
supply terminal block rating and
requirements
The following table provides information about
the functions, ratings, and requirements for the
Table 4: Communications bus and supply power terminal blocks, functions, ratings, requirements, and
cables
Terminal block/Port
Terminal labels
label
+
-
COM
FC BUS or SA BUS
SHLD
or
SAPWR
HOT
24~
COM
8 IOM3731-0A Expansion Input/Output Installation Guide
expansion module's communication bus and supply
power terminals. It also provides guidelines for wire
sizes, cable types,and cable lengths when wiring
the expansion module communication buses and
supply power. In addition, 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.
Function, electrical ratings/Requirements
FC or SA Bus Communications
Signal Reference (Common) for FC or SA Bus
communications
SHLD on FC Bus: Isolated terminal (optional shield
drain connection
SAP WR on SA Bus: 15 VDC power lead connection
Note: The SA PWR terminal on an IOM
controller does not supply 15 VDC. The SA
Bus supervisor (FAC, FEC, or VMA) supplies
15 VDC to devices on the SA Bus requiring
power.
24 VAC Power Supply - Hot
Supplies 20-30 VAC (Nominal 24 VAC)
24 VAC Power Supply - Common
Recommended cable type
FC Bus: 0.6 mm (22 AWG) stranded,
3-wire twisted, shielded cable
recommended.
SA Bus: 0.6 mm (22 AWG) stranded,
4-wire (2 twisted-pairs), shielded
cable recommended.
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.
0.8 mm to 1.0 mm
(18 AWG) 2-wire