What must SPDs limit in order to protect electrical systems effectively?

Surge Protective Devices (SPDs) are specifically designed to limit surge voltages that can occur due to lightning strikes or other surge events, such as switching operations in electrical systems. By doing so, SPDs protect sensitive electrical equipment from voltage spikes that can cause damage or induce failure. Properly limiting surge voltages helps maintain operational reliability and safety in electrical systems.

Power frequencies, while important in the context of overall electrical performance, do not pose the same immediate risk as surge voltages when it comes to damage from transients. Ground currents and environmental factors also play roles in electrical system safety, but they are managed through different types of protective equipment and strategies. Therefore, the most relevant function of an SPD is its ability to clamp or limit surge voltages effectively, ensuring that connected equipment remains safe and operational during events that could otherwise lead to significant electrical anomalies or failures.