User`s manual

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MELSEC
2 EMC COMMAND
2.1.3 Cable
Because the cable that runs from the control panel contains high frequency noise,
outside the control panel it acts as an antenna and radiates noise. Always use shielded
cable for cable that runs outside the control panel.
Except for certain models, using the ferrite core is not mandatory. However, the noise
radiated via cable can be suppressed more effectively by mounting a ferrite core.
Using a shielded cable is also effective in raising noise resistance. The signal lines
used for PLC input/output and special units are designed to ensure a noise resistance
level of 2 kV (IEC801-4/EN61000-4-4) if a shielded cable is used. If a shielded cable is
not used, or when a shielded cable is not grounded properly, the noise resistance will
drop below 2 kV.
Note : With the EN50082-2, the noise resistance of each signal line is specified based
on the application of the signal.
Signals related to control (process control) : 2 kV
Signals not related to control (process control)) : 1 kV
In the EN50082-2, the meaning of “(signals) related to control” is not defined. However,
considering the original intent of the EMC command, the signal line that poses possible
danger to person or equipment when the panel is incorrectly operated shall be defined
as the “signal related to control,” and high noise resistance is considered mandatory.
(1) Grounding treatment for shields
(a) Perform shielding processing at a position near the exit of the control panel.
If the grounding point is far from the exit position, the cable portion after the
grounding point will cause electromagnetic induction and generates high-
frequency noise.
(b) Use a grounding method that allows the shield a surface grounding in a large
area against the control panel. A clamping fixture as shown below may
alternatively be used. When such a fixture is used, mask the coating in the
area inside the control panel where the fixture contacts.
Shielded section
Screw
Clamping fixture
Coating mask
Shielded cable
Note : The method shown below in which a PVC electric wire is soldered to the
shield of the shielded cable and that end is grounded, increases the high
frequency impedance and the effectiveness of the shield is lost.
Shielded cable
PVC electric wire
Crimp contact