LVD-EOMU02U-EN REVB 04/2022
9
Modbus-RTU cable requirements
Make sure you use cable with the following specification for reliable Modbus-RTU performance.
Use shielded twisted-pair cable with a twisted pair for data and a wire or another pair for signal ground (nominal
impedance 100 to 165 ohm, for example Belden 9842) for the wiring. For best immunity, ABB recommends high quality
cable. Keep the cable as short as possible.
Avoid unnecessary loops and parallel runs near power cables such as motor cables.
BUS Cable
Transmission rate
38.4 kbit/s
Construction
2 cores, twisted, with common shield
Conductor cross section
> 0.22 mm² (24 AWG)
Twisting rate
> 10 per meter (symmetrically twisted)
Core insulation
Polyethylene (PE)
Resistance per core
< 100
Ω
/km
Characteristic impedance
ca. 120
Ω
(100
Ω
...150
Ω
)
Capacitance between cores
< 55 nF/km (if higher, the max. bus length must be reduced)
