Predicting Let-Through Arc-Flash Energy for Current-Limiting Circuit Breakers

IEEE 1584, “Guide for Performing Arc-Flash Incident Energy Calculations,” provides a method to conservatively predict the incident energy let-through by over-current devices based on the device´s time-current curve or tested transfer functions. Additional testing by various manufacturers has shown that current-limiting (CL) circuit breakers (CBs) operating in their instantaneous CL range perform significantly better than what the IEEE 1584 Time-Current Curve-based model predicts. The authors will present an analytical method to estimate the incident energy from published CB let-through curves. The method will provide a conservative, yet better, estimate of the actual performance when compared to test data. This method can be used as a part of hazard risk planning rather than the Time-Current Curve method described in IEEE 1584 or when the manufacturer does not provide an incident-energy transfer function based on tests.