Use the following limits as installation acceptance criteria for the documented PLC system. The evidence includes generic PLC guidance and several FX-series details, but it does not identify an exact model. Confirm model-specific terminal ratings and environmental limits before commissioning.
Control the Installation Environment
Keep ambient temperature within 0–50°C, relative humidity at or below 85%, and the PLC free from condensation, direct sunlight, corrosive or flammable gases, metal chips, dust, oil, and water splash. Avoid continuous or frequent vibration at 10–55 Hz with 0.5 mm peak-to-peak displacement and shock exceeding 10g.
| Installation item | Evidence-based requirement | Field decision |
|---|---|---|
| Unit spacing | Maintain at least 30 mm between the base and expansion units. | Preserve ventilation space inside the enclosure. |
| Electrical separation | Maintain at least 200 mm from high-voltage equipment and power conductors. | Avoid parallel routing where practical. |
| Mounting | Use the unit mounting holes or DIN rail with retaining clamps. | Tighten the mounting hardware and prevent movement. |
| Foreign material | Prevent wire ends and metal chips from entering ventilation openings. | Cover the PLC during panel fabrication and wiring. |
The evidence also calls for forced ventilation above 55°C, while separately limiting the environment to 0–50°C. It does not resolve the 50–55°C range or establish that a fan permits operation above the PLC rating. Treat 50°C as the stated limit until the exact model documentation confirms otherwise.
Wire Power and Grounding
The documented supply is 50 Hz, 220 VAC ±10%, equivalent to 198–242 VAC by calculation. A power interruption shorter than 10 ms is stated not to affect operation. An interruption longer than 10 ms, or voltage below the allowed range, stops the PLC and turns off all outputs. After power returns, operation resumes automatically when the RUN input is on. Where power-line interference is severe, the evidence permits a 1:1 isolation transformer to reduce equipment-to-ground interference.
- Connect the base unit directly to the grounding point using a dedicated conductor located as close to the PLC as practical.
- Bond expansion-unit grounding points to the base-unit grounding point.
- Keep the PLC ground separate from motor and other power-equipment grounds. If a shared ground is unavoidable, use a common grounding point; do not daisy-chain the PLC ground through other equipment.
- Verify that loss and restoration of supply produce the documented output-off and RUN-restart behavior before releasing the machine.
Protect 24 VDC and Input Circuits
FX-series units in the evidence provide a 24 VDC terminal for input sensors such as proximity and photoelectric switches. With passive-contact input devices, the internal supply provides 7 mA per active input point. When this terminal powers sensors, COM is the 24 VDC return. Connect the base and expansion 24 V terminals where expansion is used, but never connect an external power supply to the PLC 24 V terminal. An overload causes the voltage to fall and prevents the affected input from operating. No total external-current rating is provided, so determine the allowable sensor load from the exact model documentation.
Inputs accept passive contacts or open-collector NPN devices. Keep input wiring within 30 m unless measured voltage drop and site interference justify a longer run. Separate input and output conductors rather than placing them in the same cable. Ensure an input pulse remains present longer than the PLC scan time. If an input contact circuit contains a series diode, keep its voltage drop below 4 V; for an LED-equipped reed switch, use no more than two series diodes. Do not use unused FX-series terminals.
Protect Outputs and Hazardous Loads
The evidence identifies relay, thyristor, and transistor output forms. Different output groups may use different supply types and voltage levels, but every output within one group must use the same supply type and voltage level. Protect output elements with fuses because a load short circuit can damage the printed circuit board. Inductive loading also affects relay-output service life, although no allowable load or life curve is supplied.
Route AC and DC output wiring in separate cables, keep outputs away from high-voltage and power conductors, and avoid parallel runs. Control load-generated electrical noise at its source. For loads capable of injuring personnel, provide an external emergency-stop circuit that removes load power if the PLC fails; program logic alone is not the required protective path.
FAQ
How much clearance should I leave around a PLC?
Maintain at least 30 mm between the base and expansion units and at least 200 mm between the PLC and high-voltage equipment or power wiring.
What happens when PLC power is interrupted for more than 10 ms?
The documented PLC stops and turns off all outputs. When power returns, it resumes automatically if the RUN input is on.
Can I connect an external 24 VDC supply to the FX-series 24 V terminal?
No. The evidence explicitly prohibits connecting an external supply to that terminal; use it only within the documented internal-supply arrangement and verify the exact model's available sensor current.
