How to Avoid SPD Failure in Electrical Systems

Common Issues and Solutions for SPD (Surge Protective Devices) in Practical Applications

SPDs (Surge Protective Devices) often encounter several common issues in real-world applications:

• The maximum continuous operating voltage (Uc) is lower than the highest possible operating voltage of the power grid;

• The voltage protection level (Up) exceeds the impulse withstand voltage (Uw) of the equipment being protected;

• Improper energy coordination between multi-stage SPDs (e.g., lack of coordination or incorrect staging);

• SPDs have degraded (e.g., status indicator window changed color, remote alarm triggered) or are visibly damaged (e.g., burnt, cracked) but have not been replaced in time;

• SPDs are not actually installed in critical distribution panels (e.g., main switchboard, sub-distribution panel, equipment front-end), yet the inspection report falsely indicates they are (false installation);

• The cross-sectional area of the SPD grounding conductor is inadequate (≥16mm² for Type I, ≥10mm² for Type II, ≥4mm² for Type III, copper conductor);

• No suitable backup protective device (e.g., fuse or circuit breaker) is installed upstream of the SPD.

These issues may lead to serious consequences:

• SPD fails to effectively suppress overvoltage, resulting in equipment breakdown and damage;

• Degraded SPDs may cause short circuits leading to fire;

• Undersized grounding conductors may melt during surge current discharge, causing safety accidents;

• Without a backup protection device, a short-circuit fault in the SPD could trigger an electrical fire.

To ensure SPD effectiveness and safety, the following measures should be taken:

• Select SPDs strictly based on the withstand voltage rating of the protected equipment and installation location (e.g., lightning protection zones LPZ0–1, LPZ1–2), and ensure proper energy coordination between SPD stages;

• Install SPDs as close as possible to the power inlet of the protected equipment;

• Prioritize SPDs equipped with status indicators or remote alarm functions;

• Establish a regular inspection and timely replacement program for SPDs;

• Strictly verify the specifications of grounding conductors and ensure reliable connections;

• Always install code-compliant backup protective devices upstream of SPDs.