4-59
4 Installation and Wiring
NJ-series CPU Unit Hardware User’s Manual (W500)
4-5 Control Panel Installation
4
4-5-6 Grounding
General Precautions
• To prevent electrical shock, do not connect devices to ground poles (or steel frames) with non-
equalized potential to which multiple devices are connected.
• Use a ground pole as close to the Controller as possible and keep the ground line as short as pos-
sible.
• 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
• If high-frequency equipment is present, then ground not only the high-frequency equipment but
also the panel itself in which the Controller is housed.
• As shown in the following diagram, when using shielded cable for I/O wiring, connect the shield
near the Controller to the enclosure ground terminal. Follow the instructions in the Communica-
tions Unit manual for preparing shielded communications cable.
Controller Ground Terminals
The Controller 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.
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.
Precautions for Grounding
Protective ground terminal: Always connected to the Controller 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
The NJ-series Controllers
are designed to be
mounted so that they are
isolated (separated) from
the mounting surface to
protect them from the
effects of noise in the
installation environment
(e.g., the control panel).
Shielded Cable Ground
Controller
Output
Common
Input
Common
Controller Ground Terminals
AC side Controller side
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