Key Considerations for PLC Installation and Maintenance in Industrial Environments

Understanding the Importance of Proper PLC Installation

Programmable controllers are widely used in industrial automation due to their durability, flexibility, and ease of integration. However, to ensure long-term reliable operation, it is critical to install PLC systems correctly and consider environmental and physical factors. Proper placement and mounting not only reduce failure rates but also enhance system performance and lifespan.

When installing a PLC, avoid areas with:

• Ambient temperature beyond 0–50°C

• High humidity or condensation

• Direct sunlight exposure

• Corrosive gases (e.g., hydrogen chloride, hydrogen sulfide)

• Dust, iron filings, or mechanical vibration

• Proximity to high-voltage devices or power lines

PLC units can be fixed via screws or mounted on DIN rails with clamps. To maintain optimal temperature, leave at least 30mm of space between units and ensure adequate ventilation. If ambient temperatures exceed 55°C, consider adding forced cooling.

Power Supply Wiring Essentials

A stable and interference-resistant power supply is essential for PLC operation. The standard input for many models is 220V AC at 50Hz. If the PLC includes a 24V DC terminal, it can directly power sensors like photoelectric or proximity switches.

Some key points for wiring:

• Minor power interruptions (<10ms) won’t affect operation, but longer interruptions will halt the controller and disconnect outputs.

• If power noise is severe, use an isolation transformer (1:1 ratio) to improve signal clarity.

• Ensure proper voltage levels to prevent damage or unintended shutdowns.

Correct power wiring ensures consistent system operation and prevents disruptions caused by voltage instability.

Importance of Reliable Grounding

Grounding the PLC is not optional — it is a fundamental safety and performance requirement. Proper grounding:

• Prevents voltage shock hazards

• Reduces signal interference

• Protects internal circuitry

Each unit (basic or expansion) must be grounded to a common point close to the equipment. Avoid using a shared grounding point with heavy-duty power equipment like motors. Never connect PLC ground in series with other systems. A separate and dedicated ground wire is recommended for optimal signal integrity.

Safe Use of the 24V Terminal

The internal 24V DC terminal on a PLC can be used to power input devices or sensors. However, specific limitations apply:

• Only passive input devices (e.g., reed switches) should be used

• Do not connect external power supplies to this terminal

• Avoid overloading — exceeding current limits will cause voltage drops and prevent proper input operation

Unused input points do not consume power, allowing reallocation of the 24V supply to other components as needed. Always check the manufacturer’s current capacity for the 24V terminal to avoid potential faults.

Best Practices for Input and Output Wiring

Input wiring connects sensors to the PLC and typically handles passive contact signals or NPN transistor outputs. Key considerations include:

• Maintain input wiring under 30 meters where possible

• Separate input and output wiring entirely — never run them in the same cable

• Ensure pulse signal widths exceed the scan cycle time to guarantee detection

For output wiring:

• Choose appropriate output types: relay, transistor, or thyristor

• Use external fuses to protect internal PCB-mounted output elements

• Separate AC and DC output wiring, and avoid routing near high-voltage lines

• Always design an external emergency stop circuit for critical loads

Inductive loads can damage relays over time, so ensure proper suppression and noise control measures are in place.

Conclusion

Effective PLC installation and maintenance go far beyond simply wiring the unit into a system. From careful selection of installation location to proper grounding, power setup, and structured wiring practices, every detail impacts long-term reliability and safety. Following these best practices allows your control systems to run smoothly, reducing downtime and extending hardware life in even the most demanding industrial environments.