4-4
Section 4 Installation and Wiring
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5 When inductive load current is interrupted by a switch,
high voltage is induced between the two ends of the load,
which may affect the PLC.
1) A diode, varistor or RC should be connected to the
DC load.
2) A RC should be connected to the AC load.
(Example)
6 Malfunction due to external I/O signal lines bound
together with or installed near a high-voltage cable or
power cable
(Electromagnetic inducation, electrostatic induction)
I/O lines should be separated from other cables and
should not be wired in the same panel or pit.
Duct, independent cable pipe or metal pipe (as shown
below) should be used for isolation.
7Transmission cable malfunction or damage caused by
lightning surge
Transmission cables should run through underground
metal pipes or in an electrical duct. The metal pipes
should be grounded.
8 Malfunction of PLC located near device that
generates a switching arc
When the control panel door closed, if the distance
L between the PLC front panel and magnetic
contactor is 50mm or less, the PLC malfunctions
due to the switching arc generated by the magnetic contactor.
The device layout should be changed or a shielding
panel should be installed.
(Example)
Load
Switch
Power supply
Arc discharge
Low voltage
Surge voltage
(10 to 20 times the load voltage)
Interrupting current
Lightning
Transmission cable
Uphill
station
Downhill
station
Mountain
Metal pipe
RS-232C, RS-485, etc
Door
L
PLC
Magnetic
contactor
Shielding panel
PLC
Magnetic
contactor
Type D (Class 3) grounding
(ground resistance of 100Ω or less)
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