Kudos to the Low Voltage Distribution Section of NEMA for producing a comprehensive guide on Selective Coordination. The 47 page white paper explains the recent changes to the National Electrical Code (NEC) for the design of life safety and other critical power systems. The goal of Selective Coordination is to isolate a fault circuit while maintaining power to the rest of the electrical distribution system. In the NEC it applies to elevators, healthcare sytems, emergency systems, and legally required standby systems.
While the concept is simple – coordinate the size of the overcurrent protection devices (OCPD) so that the OCPD nearest the fault opens to clear the fault – designing such a system is a challenging task. The white paper provides the design engineer with detailed guidance on how to achieve coordination. Early feedback includes rave reviews for the document.