How do surge protective devices function at the service entrance?

Surge protective devices (SPDs) at the service entrance are designed to protect electrical systems from transient overvoltages, such as those caused by lightning strikes or switching operations in the power grid. When a surge event occurs, the primary function of these devices is to divert or limit the excessive surge currents that could potentially damage equipment and disrupt normal operations.

SPDs achieve this by using various components, such as metal-oxide varistors (MOVs) or gas discharge tubes, which respond rapidly to voltage surges. When a voltage spike is detected, these components change states to shunt the excess voltage away from sensitive equipment, effectively "catching" the surge and directing it safely to ground. This means that they do not merely allow surge currents to pass through but actively manage the excess energy to prevent damage.

While other options mention functions like amplifying surge currents, measuring voltage levels, or regulating frequency, these do not align with the primary role of SPDs at the service entrance, which is protective in nature. By diverting or limiting surge currents, SPDs play a crucial role in maintaining the integrity and longevity of electrical systems and the equipment connected to them.