Lingering lead length legacies in surge-protective devices applications

Two experiments are reported to show how some lingering inherited misconceptions about the applications of surge-protective devices (SPDs) can lead to erroneous or cost-ineffective attempts to address the issue of lead length. The first experiment demonstrates the fallacy of the "four-terminal SPD" configuration if taken at face value without additional precautions on lead dress. The second experiment provides quantitative information on the actual effect of lead length. With this information, designers and installers can place the issue in a realistic perspective and avoid unnecessary effort.