How to protect PLCs from power line lightning interference?

To protect PLCs from power line lightning strikes, a multi-stage surge protection network is required. The first stage uses a 2R600L-8×6 gas discharge tube with a current carrying capacity of 20kA (8/20μs) and a response time ≤100ns. The second stage uses a 14D511K varistor with a clamping voltage of 510V and a current carrying capacity of 6.5kA. The third stage uses a TVS diode SMCJ24CA with a clamping voltage of 38.9V and a response time ≤1ns. Decoupling inductors (10μH) or resistors (10Ω) are used between each stage to ensure energy is discharged sequentially. A surge protection box is installed at the power line inlet, with a grounding resistance of less than 4Ω. Simulation verification of the protection circuit response ensures the safety of subsequent circuits under a 6kV/3kA combined wave test. In actual testing, surge immunity testing (IEC61000-4-5) is performed, and the system should pass the ±4kV test. Protection against lightning strikes improves system reliability and reduces damage.