What is an SPD and why is it used?

• A. Converts AC to DC
• B. Acts as a surge generator
• C. Clamps transient overvoltages to protect equipment
• D. Steps down voltage

Answer: (C)

An SPD, or surge protective device, is designed to protect electrical equipment from transient overvoltages by clamping the surge and directing excess energy away from sensitive circuits, usually to ground or neutral. Transients come from sources like lightning, switching events, or faults and can push voltages well above normal levels for a brief moment. The SPD uses components such as metal-oxide varistors, gas discharge tubes, or TVS diodes that conduct when the voltage exceeds a set threshold, keeping what the equipment sees within safe limits. Properly chosen SPDs consider system voltage, clamping voltage, and energy rating, and they’re installed at key points in the system (service entrance, distribution panels) to intercept surges before they reach gear. They may degrade after a surge and should be tested or replaced after an event. Because SPDs perform this clamping function to protect equipment from transient overvoltages, they align with the correct answer. The other listed functions—converting AC to DC, generating surges, or stepping down voltage—are handled by different devices.