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11 EMC AND LOW VOLTAGE DIRECTIVE
MELSEC-ST
11.1.2 Instructions for installing into control panel
The MELSEC-ST series is open equipment and must be installed within a control
panel for use. This ensures safety as well as effective shielding of the electromagnetic
noise generated by the MELSEC-ST series.
(1) Control panel
(a) The control panel must be conductive.
(b) When fixing a top or bottom plate of the control panel with bolts, do not coat
the plate and bolt surfaces so that they will come into contact.
(c) When using an inner plate to ensure electric conductivity with the control
panel, do not coat the fixing bolt area of the inner plate and control panel to
ensure conductivity in the largest area as possible.
(d) Ground the control panel using a thick grounding cable in order to ensure
low impedance under high frequency.
(e) The diameter of cable holes in the control panel must be 10cm (3.94in.). In
order to reduce the chance of radio waves leaking out, ensure that the
space between the control panel and its door is small as possible.
Attach some EMI gaskets to fill up the space and suppress the leakage of
radio waves.
Our tests have been carried out on a panel having the damping
characteristics of 37 dB max. and 30 dB mean (measured by 3 m method
with 30 to 300 MHz).
(2) Connection of power and ground wires
Connect the ground and power supply wires for the MELSEC-ST series as
described below.
(a) The FG of power distribution module is grounded via the DIN rail.
Therefore, the grounding point to the control panel must be placed near the
DIN rail. Make sure to use a long and thick ground wire (max. 30 cm) to
ground the DIN rail. As the FG releases the noise generated inside the
MELSEC-ST series onto the ground, select the ground wire that includes the
lowest impedance as possible.
As the ground wire releases noise and wears large noise, install wiring so
that the ground wire will be short as possible, in order to prevent it from
functioning as an antenna.
(b) The ground wire coming out from the grounding point must be twisted with
the power wire. This releases more noise that flows from the power wire to
the ground. When a noise filter is attached to the power wire, this may
eliminate the necessity of twisting with the ground wire.
(c) Use a DIN rail of which surface is conductive, i.e., not insulated.
Summary of Contents for MELESEC-ST
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