Protecting Your PLC from Power Surges – Best Practices
The Threat of Voltage Spikes
Industrial power lines are susceptible to lightning strikes, motor startups, and mains fluctuations—all of which can damage a PLC's power supply or input modules. A spike above 100V on a 24V DC line can fry the CPU board instantly. Siemens S7-1200 models have built-in surge protection up to 2kV, but older units like the S7-200 need external protection devices for reliable operation.

Installing Protection Layers
Use a three-stage protection approach: (1) a Type 2 surge arrester at the main distribution panel, (2) a transient voltage suppressor (TVS) diode across the PLC's power input, and (3) shielded cables for all I/O lines with ferrite cores near the PLC terminals. For Mitsubishi FX series, installing a surge filter (e.g., Mitsubishi FR-BLF) between the mains and the PLC significantly reduces noise coupling.

Testing and Monitoring
After installation, simulate a surge (using a surge generator) to verify the protection works without tripping the breaker. Periodically check the status of surge protectors—many have an indicator window that turns red after a fault. For remote sites, use a PLC analog input to monitor the DC bus voltage and log anomalies; a sudden 5V drop may indicate an impending surge event.

• Share on:
• WhatsApp
• Deel
• X
• Pin it
• Messenger
• Email