How to properly size a motor circuit breaker? This article will tackle about the sizing of Inverse Time Circuit Breaker with regards to National Electrical Code (NEC). I have learned this not just in school, but also in review center for our national board exam. It's one of the essential topics you should know for future use especially in the design field. What is Circuit Breaker? Circuit Breaker is an over current protective device that can manually switch on/off and automatically trip when a short circuit fault occurs. Why do we need to size a circuit breaker? Circuit Breaker rating is sized according to its load/s. Thus, undersized circuit can always give false alarm to operation. While oversized can lead to equipment breakdown or