"Right Sizing” Circuit Breakers in Motor Starters

Instantaneous-trip, molded-case circuit breakers (MCCBs) have been applied successfully for low-voltage motor protection for many years. In recent years, however, the changes in motor-starting characteristics have created more difficult challenges for the application engineer. The major challenge is successfully starting the low-voltage motor without causing the instantaneous-trip breaker to falsely trip without exceeding equipment ratings or violating limitations in the National Electrical Code (NEC) [1].