Electrical surges and spikes cause damage and premature failure of machines, components and power distribution systems as well as disrupt signals in industrial control systems. Externally lightning strikes and disruptions in utility power can send high energy transients into a facility. Internally the switching of lighting circuits, contactors and other devices can cause fatigue of components or systems over time. Proper mitigation of these anomalies is imperative to maintaining a robust and reliable power system. UL 1449 sets safety and performance standards for surge protective devices (SPDs) which are identified by Type 1, 2, 3 or 4 depending on where the SPD is incorporated within the power distribution system.