NEC Design Compliance, System Protection, and Arc Flash Hazard

The National Electric Code (NEC) specifies limits on settings of transformer overcurrent protective devices that directly affect system protection. However, compliance with NEC design guidelines does not assure adequate system protection. The result can be zones of poor or nonexistent protection and “Extreme Danger” arc flash hazard (AFH) ratings. This paper discusses the existing system protection in a large paper mill and makes recommendations for improving that protection and lowering AFH ratings.