Surge protective devices are required to be installed at any point where conductors leave a structure if they are run over what distance?

Surge protective devices (SPDs) play a critical role in safeguarding electrical systems from transient overvoltages, such as those caused by lightning strikes or power surges. The requirement for the installation of SPDs is specifically tied to the length of conductors leaving a structure. When conductors exceed a distance of 100 feet, they become more susceptible to induced voltages and electromagnetic interference. This is primarily because longer conductors can act analogously to antennas, capturing surges from the environment or from nearby electrical systems.

By installing surge protective devices at this distance threshold, the risk of equipment damage due to surges is significantly mitigated. These devices help to intercept and redirect excess voltage away from sensitive systems, ensuring continuity and reliability in electrical performance. Therefore, the requirement for SPDs to be installed at points where conductors leave a structure is stipulating a necessary safety measure for conductors run over 100 feet to protect both infrastructure and equipment from potential lightning-related damage.