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5 Installation
CJ2 CPU Unit Hardware User’s Manual
5-4 Control Panel Installation
5
5-4-6 Grounding
z Precautions when Grounding
• If the same ground is used for both the signal lines and the enclosure, isolate the channel base
(a grounded metal plate inside a control panel) with an insulating material
• To prevent influence from leakage current from other electrical devices, electrically isolate the
panel in which the PLC is housed from other devices.
• If high-frequency equipment is present, then ground not only the high-frequency equipment but
also the panel itself in which the PLC is housed.
• As shown in the following diagram, when using shielded cable for I/O wiring, connect the shield
near the PLC to the enclosure ground terminal. Follow the instructions in the Communications
Unit manual for preparing shielded communications cable.
z PLC Ground Terminals
The PLC has the following two ground terminals.
When the functional ground terminal is correctly grounded, it is generally effective in suppressing
power supply common noise. Occasionally, however, grounding this terminal will result in picking up
more noise, so be careful when using it.
z Grounding for AC Power Supply Units
When wiring to an AC Power Supply Unit, if one power supply phase of the equipment is grounded,
always connect the grounded phase to the L2/N terminal.
Protective ground terminal: Always connected to the PLC chassis to prevent electrical shock.
Functional ground terminal: Connected to a neutral point in the noise filter to provide a ground when
power supply noise causes malfunctioning.
Example: Insulating and Grounding an Enclosure
Insulating material
Channel base
Independent ground
CS/CJ-series PLCs
have an isolated
(floating) mounting
structure to make it
more difficult to be
affected by noise from
an installation
environment, such as
a control panel.
Shielded Cable Ground
PLC
Output
Common
Input
Common
PLC Ground Terminals
AC side PLC side
L1
L2/N
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