Rs485 I/O And Modbus Devices (Except Control Link); Control Link Modules; Emi-Resistant Rs485 Network Grounding Practices - Emerson E2 Einstein Manual

If the network is experiencing problems with
EMI or is known to be in a high-noise environment,
follow the EMI-resistant wiring guidelines for
grounding the shield wire outside the E2 enclosure
(Section 7.3.1., Ground the Shield Outside of the
E2).
7.2.2. RS485 I/O and MODBUS De-
vices (except Control Link)
7.2.2.1. Grounding the Power Connec-
tor Terminal
Each RS485 I/O and MODBUS device, includ-
ing both devices that are powered by center-tapped
transformers and devices powered by non-center-
tapped transformers, must have the 0V terminal of
the power connector connected to a separate earth
ground. "Separate" earth ground means you may
NOT wire the 0V connectors of multiple boards in
series and ground at one point. Each 0V terminal
must be earth grounded separately. Connect each 0V
terminal for all networked devices earth grounds,
using ground wires at least 14AWG and no longer
than six inches.
7.2.2.2. Grounding the Network Cable
The shield wires of the network cable are nor-
mally connected to the center (0V) terminal of the
RS485 I/O connector. Provided the power inputs are
properly grounded, you do not need to connect the
center (0V) terminals to separate earth grounds, since
the center pins of both the power and network con-
nectors are common on the board.
If the network is experiencing problems with
EMI or is known to be in a high-noise environment,
follow the EMI-resistant wiring guidelines for
grounding the shield wire outside the E2 enclosure
(Section 7.3.1., Ground the Shield Outside of the
E2).

7.2.3. Control Link Modules

The Control Link Module does not have a
ground terminal on its power output. The only
ground connection on the Control Link that needs to
be earth grounded is the "Common" terminal on the
top input block (see Figure 7-1). The ground wire

EMI-Resistant RS485 Network Grounding Practices

should be at least 14AWG stranded, no longer than
six inches, and should be routed away from all high-
voltage wiring leading from the power input and the
relay outputs.
Figure 7-1 - Earth Ground Connection Location
7.3. EMI-Resistant RS485
Network Grounding
Practices
If you are experiencing network problems that
might be related to noise, it is best to eliminate the
noise path at the device itself and through earth
grounding prevent the noise from traveling through
the cable into the E2.
Begin by identifying potential sources of noise,
and identifying what I/O or MODBUS devices are
near the noise source or connected (by cable) to the
noise source (refer to Section 1.2. and Section 2 for
common noise sources). For example, a MultiFlex
168AO connected to a VSD drive by analog output
cable would be a possible source of harmful noise.
For I/O and MODBUS devices connected to or
near high-noise devices:
1. Ensure the power connector is connected to a good
earth ground as per Section 7.2.2.1.
2. Remove the shield wire(s) connected to the 0V (cen-
ter terminal) of the RS485 network connector (leave
nothing connected to the 0V terminal).
3. Connect the network cable shield wire to the same
earth ground the power connector is connected to. For
Cable and Device Grounding • 11