Troubleshooting PV Surge Protective Devices: Common Failures and How to Fix Them

Surge protective devices (SPDs) play a vital role in safeguarding solar photovoltaic (PV) systems from transient overvoltages and lightning strikes. However, like all protective components, SPDs can fail over time. Recognizing the signs of SPD failure and knowing how to troubleshoot them is critical to maintaining system safety and reliability. In this guide, we explain the most common SPD problems, their causes, and practical steps to fix them.

1. Why PV SPDs Fail

SPDs are designed to absorb or divert surge energy. With repeated exposure to surges, they gradually degrade. Key causes of SPD failure include:

• Lightning Strikes: Direct or indirect strikes cause high-energy surges that wear down SPD components.
• Switching Surges: Sudden load switching in the grid or PV system creates transient overvoltages.
• Poor Installation: Incorrect wiring or inadequate grounding reduces SPD effectiveness.
• Overvoltage Stress: Using SPDs with ratings below the system’s maximum voltage causes premature breakdown.
• Environmental Stress: Heat, humidity, and dust accelerate SPD degradation.

2. Common SPD Failures in PV Systems

• Overheating: Caused by prolonged overvoltage stress or poor ventilation. Signs include melted casing, discoloration, or burnt smell.
• Tripping of Thermal Disconnects: SPDs often contain thermal fuses that disconnect when overheated. A tripped SPD is no longer functional.
• Loss of Protection (Open Circuit): SPD appears intact but no longer diverts surge currents.
• Short Circuit Failure: Rare, but possible if the MOV (metal oxide varistor) inside the SPD fails catastrophically.
• Indicator Light Failure: Green/red LEDs or windows may malfunction, making it difficult to know SPD status.

3. How to Diagnose SPD Problems

Step-by-step troubleshooting process:

1. Visual Inspection: Look for damage such as cracks, burn marks, or melted parts.
2. Check Status Indicators: Most SPDs have windows or LEDs showing “healthy” (green) or “faulty” (red/off).
3. Test Continuity: Use a multimeter to check if the SPD is still conducting properly.
4. Check Remote Signals: For SPDs with remote contacts, verify alarms through monitoring systems.
5. Grounding Check: Ensure all grounding connections are secure and low resistance.

4. Solutions for Common Failures

• Overheating: Improve ventilation, reduce system voltage stress, and replace overheated SPD immediately.
• Tripped SPD Module: Replace the cartridge/module with a manufacturer-approved spare.
• Loss of Protection: Replace degraded SPD—never assume an “open” SPD still works.
• Short Circuit Failure: Disconnect the SPD, isolate the circuit, and install a new SPD with correct ratings.
• Indicator Light Failure: Cross-check with remote signaling or perform electrical testing before replacement.

5. Preventive Maintenance Tips

To reduce SPD failures and extend their lifespan, follow these practices:

• Use SPDs with proper voltage ratings (Uc higher than PV array maximum voltage).
• Install SPDs in enclosures with adequate cooling and IP protection.
• Perform quarterly inspections of status indicators and grounding.
• Document SPD replacements and surge events for long-term tracking.
• Integrate SPDs into SCADA monitoring systems for real-time alerts.

6. Common Mistakes in Troubleshooting

• Relying Only on Visual Checks: Indicators can fail—always confirm with electrical testing.
• Mixing AC and DC SPDs: DC-rated SPDs must be used in PV applications.
• Ignoring Ground Resistance: High resistance grounding reduces SPD effectiveness.
• Delaying Replacement: Running the system with a failed SPD exposes all equipment to risk.

7. FAQ Section

Q1: How often should I check my PV SPDs?
A: Monthly for visual checks, quarterly for electrical testing, and after every major storm event.

Q2: Can SPDs be repaired?
A: No. Once degraded, SPDs must be replaced with certified parts.

Q3: Why does my SPD keep failing?
A: Possible causes include undervalued SPD ratings, poor grounding, or unusually high surge activity.

Q4: What happens if I ignore a failed SPD?
A: The solar system becomes vulnerable to surges, leading to inverter or panel damage costing thousands of dollars.

8. Conclusion

Troubleshooting PV surge protective devices (SPDs) is an essential skill for installers, operators, and maintenance teams. By identifying overheating, tripping, or degraded SPDs early, you can prevent catastrophic solar system failures. Remember: SPDs are sacrificial devices designed to protect more valuable equipment—when in doubt, replace them immediately to ensure continuous system safety.