ABB NMBA-01 - Earthing the Modbus Cable Shields

Chapter 4 – Electrical Installation
4-4 NMBA-01 Installation and Start-up Guide
Earthing the Modbus
Cable Shields
The Modbus cable shield may be directly earthed at one station only. At
other stations the cable shield should be earthed via an RC filter.
There are two wiring examples in the figures below. The three-wire
connection is the preferred one because of its the better noise
immunity.
Figure 4-3 Two-wire Connection.
Figure 4-4 Three-wire Connection. (Preferred Practice.)
3 2 14
SHF
DG
D(N)
A B
X2
100 Ω
NMBA-01
[Station 1]
Termination: OFF
3 2 14
SHF
DG
D(N)
X2
100 Ω
[Station N]
Termination: ON
...
Modbus Master
Termination: ON
GND
D(P) D(P)
NMBA-01
3
2 14
SHF
DG
D(N)
A B
X2
100 Ω
NMBA-01
[Station 1]
Termination: OFF
3 2 14
SHF
DG
D(N)
X2
100 Ω
[Station N]
Termination: ON
...
Modbus Master
Termination: ON
GND
D(P) D(P)
NMBA-01
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