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Communications bus and supply power wiring guidelines
Table 5 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 5, 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 following documents depending on your system (FX or BCPro): FX-PC Series
Controllers MS/TP Communications Bus Technical Bulletin (LIT-12011670) or MS/TP Communications
Bus for BCPro System Technical Bulletin (LIT-12011908) 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 5: Communications bus and supply power terminal blocks, functions, ratings,
requirements, and cables
Terminal block/
Terminal
Port label
labels
FC BUS
+
or
-
COM
SA BUS
Figure 8: Maximum wire length for low-voltage
(<30 V) Inputs and Outputs by current and wire size
Function, electrical ratings/
Requirements
FC or SA Bus Communications
Signal Reference (Common) for FC
or SA Bus communications
FX-PCX2721 Expansion Input/Output Module Installation Instructions
Recommended cable type
FC Bus: 0.6 mm (22 AWG)
stranded, 3-wire twisted,
shielded cable recommended.
17
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