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20. EMC AND LOW VOLTAGE DIRECTIVES
20.1.3 Cables
The cables running from the control panel contain a high frequency noise component, and
outside the control panel, they release noise acting as antennas. Always use shielded
cables when cables connected to I/O modules and/or special modules are to be brought
out from the control panel.
Attaching ferrite cores is not required except some CPU types, however, using ferrite
cores can restrain noise emanated via cables.
Using shielded cables also increase noise resistance. The signal lines (including common
line) of the PLC, which are connected to I/O modules and/or special modules, have noise
resistance compliant with EN61131-2/A12(2000) in the condition that shielded cables are
to be used. If shielded cables are not used, or if grounding of shielded cables is not
correct, the noise resistance will be less than the specified value.
(1) Grounding of shielded cables
(a) Shielding must be done close to the control panel. Otherwise, electromagnetic
induction from the cable after the grounding point will generate high frequency
noise.
(b) Partly remove the outer sheath of the shielded cable so that it can be contact
with the widest possible area of the control panel. A clamp may also be used as
shown in the figure below.In this case, cover the control panel's inner surface
which will come in contact with the clamp when painting.
Note)
Grounding a shield cable by soldering a wire to the shield section as
illustrated below is not recommended. The high frequency impedance
will increase and the shield will be ineffective.
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