Current and Surge Protective Devices

Specifications use several current-related terms to describe the capacity of a Surge Protective Device (SPD) to withstand or manage specific types of current. The following narrative defines the terms Surge Current, Short Circuit Current, Nominal Discharge Current, and Fault Current, and explains how they relate to SPDs. 


When excessive transient overvoltages occur, SPDs must shunt the excess energy and survive the event. The amount of current that an SPD can safely shunt is its Surge Current Rating, which is also known as Surge Capacity. This can be presented as a per mode or per phase rating and the resulting value is specified in thousands of amperes (kA). Alternatively, this rating may be published as a total surge current rating for the SPD, which may be estimated by summing the current capacity of its surge components, or verified by testing the SPD as a complete assembly.