9. EMC DIRECTIVE AND LOW-VOLTAGE INSTRUCTION
9 - 11
MELSEC-
9.2.6 Grounding
There are two kinds of grounding terminals as shown below. Either grounding
terminal must be used grounded.
Be sure to ground the protective grounding for the safety reasons.
Protective grounding : Maintains the safety of the PLC and improves
the noise resistance.
Functional grounding : Improves the noise resistance.
9.2.7 External wiring
(1) 24 V DC external power supply
For special modules that require a 24 V DC I/O module or external power
supply, use a model whose 24 V DC circuit is intensively insulated from the
hazardous voltage circuit.
(2) External devices
When a device with a hazardous voltage circuit is externally connected to the
PLC, use a model whose circuit section of the interface to the PLC is
intensively insulated from the hazardous voltage circuit.
(3) Intensive insulation
Intensive insulation refers to the insulation with the dielectric withstand voltage
shown in Table 2.
Table 2 : Intensive Insulation Withstand Voltage (Installation
Category II, source : IEC664)
Rated voltage of hazardous voltage area Surge withstand voltage (1.2/50
µ
µµ
µ
s)
150 V AC or below 2500 V
300 V AC or below 4000 V
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