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5. EMC DIRECTIVE, LOW VOLTAGE DIRECTIVE
5.1.3 Cables
Cables drawn from the control box include high-frequency noise components and act
as antennas outside the control box to radiate noise. Cables connected to the I/O
and special modules and drawn to outside the control box must be shielded cables.
With the exception of some models, cables are not required to be fitted with ferrite
cores. However, fitting of ferrite cores can further suppress noise radiated via cables.
Use of shielded cables are also effective to increase noise immunity.
The signal lines of the PLC I/O and special modules reserve the noise immunity of
2kV in IEC801-4/EN61000-4-4 under the conditions of using shielded cables. If you
do not use shielded cables or if you use them but do not ground their shields properly,
noise immunity is less than 2kV.
Note: EN50082-2 sets forth noise immunity according to the signal line application.
Signals related to process control
Signals not related to process control
EN50082-2 does not define the meaning of "related to process control". However,
given the spirit of the EMC Directive, we understand signal lines which may endanger
people or equipment due to a malfunction should be defined as "signals related to
process control" and require high noise immunity.
(1) Shield grounding
(a) Ground a shield at a point near the outlet of a cable from a control box. If the
grounding point is away from the outlet position, the cable after the grounding
point will cause electromagnetic induction again, generating high-frequency
noise.
(b) Take appropriate measures so that the shield section of the shielded cable
from which the outer cover was partly removed for exposure is earthed to the
control panel on an increased contact surface. A clamp may also be used as
shown in the figure below. In this case, however, apply a cover to the painted
inner wall surface of the control panel which comes in contact with the clamp.
Note: If a vinyl wire is soldered to the shield of the shielded cable and the end of
that wire is grounded, this grounding method will increase high-frequency
impedance and eliminate the effect of the shield.
: 2kV
: 1kV
Shield
Paint masking
Shielded cable
Vinyl wire
Solderless terminal
5 - 4
MELSEC-A
Screw
Clamp fixture
Shielded cable
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