Installation Instructions For Emc Directive - Mitsubishi Electric MELSEC-A series User Manual

3.1.2 Installation instructions for EMC Directive

The programmable controller is open equipment and must be installed within a
control cabinet for use.* This not only ensures safety but also ensues effective
shielding of programmable controller-generated electromagnetic noise.
* : Also, each network remote station needs to be installed inside the control
panel.
However, the waterproof type remote station can be installed outside the
control panel.
(1) Control cabinet
(a) Use a conductive control cabinet.
(b) When attaching the control cabinet's top plate or base plate, mask
painting and weld so that good surface contact can be made between
the cabinet and plate.
(c) To ensure good electrical contact with the control cabinet, mask the
paint on the installation bolts of the inner plate in the control cabinet so
that contact between surfaces can be ensured over the widest possible
area.
(d) Earth the control cabinet with a thick wire so that a low impedance
connection to ground can be ensured even at high frequencies.
(e) Holes made in the control cabinet must be 10 cm (3.94 in.) diameter or
less. If the holes are 10 cm (3.94 in.) or larger, radio frequency noise
may be emitted.
(f) Lock the control panel so that only those who are trained and have
acquiredenough knowledge of electric facilities can open the control
panel.
(2) Connection of power and earth wires
Earthing and power supply wires for the programmable controller system
must be connected as described below.
(a) Provide an earthing point near the power supply module. Earth the
power supply's LG and FG terminals (LG : Line Ground, FG : Frame
Ground) with the thickest and shortest wire possible. (The wire length
must be 30 cm (11.18 in.) or shorter.) The LG and FG terminals function
is to pass the noise generated in the programmable controller system to
the ground, so an impedance that is as low as possible must be ensured.
In addition, make sure to wire the ground cable short as the wires are
used to relieve the noise, the wire itself carries large noise content and
thus short wiring means that the wire is prevented from acting as an
antenna.
(b) The earth wire led from the earthing point must be twisted with the power
supply wires. By twisting with the earthing wire, noise flowing from the
power supply wires can be relieved to the earthing. However, if a filter is
installed on the power supply wires, the wires and the earthing wire may
not need to be twisted.
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