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20. EMC AND LOW VOLTAGE DIRECTIVES
20.1.2 Installation inside the control panel
The PLC is open equipment and must be installed within a control panel for use.* This is
effective not only for ensuring safety but also for shielding electromagnetic noise
generated from the PLC.
* Each network remote station also needs to be installed inside the control panel.
However, waterproof type remote stations can be installed outside the control panel.
(2) Control panel
(a) Use a conductive control panel.
(b) When fixing the top or base plate with bolts, mask the fixing area when painting
so that an electrical contact can be made.
(c) To ensure an electrical contact with the control panel, mask the bolt areas of the
inner plates when painting to allow conductivity over the widest possible area.
(d) Ground the control panel with a thick wire so that a low impedance can be
ensured even at high frequencies.
(e) Holes made in the control panel must be 10cm (3.94inch) diameter or less. If the
diameter is more than 10cm (3.94inch), radio waves can be leaked.
(3) Connection of power cable and ground wires
Handle the power cables and ground wires as described below.
(a) Provide a grounding point near the power supply module. Ground the power
supply module's LG and FG terminals (LG : Line Ground, FG : Frame Ground)
with the thickest and shortest wire possible. (The wire length must be 30cm
(11.18inch) or shorter.)As the LG and FG terminals release the noise generated
in the PLC to the ground, the lowest possible impedance must be ensured.
The ground wires also need to be short as they are used to release noise.
Because the wire itself carries large noise, short wiring prevents it from acting as
an antenna.
(b) Twist the ground wire led from the grounding point with the power cable. By
doing this, noise from the power cable can be released to the ground. If a filter is
attached to the power cable, however, this twisting may not be needed.
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