NEC 240.67 Arc Energy Reduction Technical Paper

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NEC 240.67 is a requirement that relates to arc-fault currents, which is not explicitly defined in NEC. IEEE 1584- 2018 defines arc current as “A fault current flowing through an electrical arc plasma.” Due to the added impedance of the electrical arc plasma, the value of an arcing fault current will always be less than the bolted fault potential. Typically, an estimated bolted fault current potential for a given system is known. However, arc currents may not always be provided for the same system. Using the estimated bolted fault potential and other system parameters, a minimum available arcing current can be calculated using equations in IEEE 1584-2018, IEEE Guide for Performing Arc Flash Hazard Calculations. This document replaces IEEE 1584-2002, which is referenced in “Informational Note No. 3” of NEC 240.67. Unfortunately, the upper bound of IEEE 1584-2018 is 106 kA. When an electrical system can deliver more than 106 kA to the fuse installation point, there is not an industry accepted method of calculating arcing currents based on bolted fault currents. Call 1-800-TEC-FUSE or email for technical support when a system’s bolted fault current exceeds 106 kA.