The National Electric Code (NEC) defines selective coordination as the “localization of an overcurrent condition to restrict outages to the circuit or equipment affected, accomplished by the choice of overcurrent protective devices and their ratings or settings.” Simply put, in a well-coordinated electrical system faults are isolated by having only the closest upstream breaker or fuse operate, leaving the rest of the electrical system in operation. Selective coordination requirements have increased with successive revisions of the NEC (NFPA-70) and as of 2008 cover 5 scenarios: health care facility essential systems, multi-elevator systems, emergency systems, legally-required standby systems and critical operation power systems. Achieving selective coordination requires the design engineer to carefully study the ratings of numerous components, as well as coordinate with the electric utility to understand the characteristics of the supply system.