8 EMC AND LOW VOLTAGE DIRECTIVE

8.2.5 Grounding

MELSEC-Q

There are the following two different grounding terminals.

Use either grounding terminal in an earthed status.

Protective grounding : Maintains the safety of the PLC and improves the noise resistance.

Functional grounding : Improves the noise resistance.

8.2.6External wiring

(1)24VDC external power supply

For the MELSEC-Q series PLC 24VDC I/O modules and the intelligent function modules (special function modules) which require external supply power, use a model whose 24VDC 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 8.1.

Table 8.1 : Intensive Insulation Withstand Voltage (Installation Category II, source : IEC664)

Rated voltage of hazardous voltage area

Surge withstand voltage (1.2/50 s)

150VAC or below

2500 V

300VAC or below

4000 V

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