User`s manual

22
FX3U Series Programmable Controllers
User’s Manual - MODBUS Serial Communication Edition
4 Wiring
4.3 Selecting Cables and Terminal Resistors (MODBUS RS-
4.3 Selecting Cables and Terminal Resistors (MODBUS RS-485)
Select cables using the procedure described below.
4.3.1 Twisted pair cable
Use shielded twisted pair cables for connecting communication equipment operating in accordance with
MODBUS RS-485.
1. Cable structural drawing (reference)
2. RS-485 cable specifications
Item Description
Cable type Shielded cable
Number of pairs 2p, 3p
Conductor resistance (20°C) 88.0 Ω/km or less
Insulation resistance 10000 MΩ-km or more
Dielectric withstand voltage 500VDC, 1minute
Electrostatic capacitance (1 kHz) 60nF/km or less by an average
Characteristic impedance (100 kHz) 110±10 Ω
Example of two-pair cable
structural drawing
Pair
Shield
Example of three-pair
cable structural drawing