company news about When a Surge Protective Device (SPD) fails, the root cause is not always a surge.

When a Surge Protective Device (SPD) fails, the root cause is not always a surge.

Our team examined an AC surge protective device (SPD) from a photovoltaic power plant that catastrophically failed. The investigation revealed that the failure was not caused by lightning or transient overvoltage, but by a wiring error during panel assembly: an unintended phase-to-enclosure (phase-to-ground) fault.

This is an important reminder for all PV engineers:

• An SPD is designed to limit transient overvoltages, not to withstand sustained power-frequency faults.
• A prolonged phase-to-ground fault can drive the SPD beyond its thermal and electrical limits, resulting in thermal runaway and catastrophic rupture.
• Correct coordination between the SPD, upstream overcurrent protective devices, and the earthing system is essential, but no protection device can compensate for incorrect wiring.
• Thorough inspection, insulation resistance testing, continuity verification, and commissioning procedures before energization remain the first line of defense.

This incident reinforces a fundamental engineering principle:

As our industry continues to build larger and more reliable solar power plants, sharing real field failures is one of the most effective ways to improve engineering practices and prevent repeat incidents.