Installation Inside The Control Panel - Mitsubishi Electric MELCEC Q Series User Manual

8. EMC AND LOW VOLTAGE DIRECTIVES
8.1.2

Installation inside the control panel

The programmable controller is open equipment and must be installed within a control
panel for use.
electromagnetic noise generated from the programmable controller.
(1)
(2)
*
This is effective not only for ensuring safety but also for shielding
* 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.
Control panel
(a) Use a conductive control panel.
(b) When attaching the control panel's top plate or base plate, mask painting and
weld so that good surface contact can be made between the panel and the bolt.
(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 ground wire so that a low impedance can
be ensured even at high frequencies.
(e) Keep the diameter of the holes on the control panel to 10cm or less. If the
diameter is larger than 10cm, electromagnetic wave may leak. In addition,
because electromagnetic wave leaks through a clearance between the control
panel and its door, reduce the clearance as much as possible. Use of EMI
gaskets (sealing the clearance) can suppress undesired radiated emissions.
We carries out the tests on the panel having the damping characteristics of 37dB
max. and 30dB mean (measured by 3m method with 30 to 300MHz).
(f) Lock the control panel so that only those who are trained and have acquired
enough knowledge of electric facilities can open the control panel.
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 or
shorter.) As the LG and FG terminals release the noise generated in the
programmable controller 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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