Low-voltage circuit breakers interrupting capacity ratings and short-time current ratings define different circuit breaker performance characteristics. Electrical Engineers use these ratings to select the protective device ratings to suit their application. The Electrical Engineer should have a good understanding of interrupting capacity and short-time current ratings to make a proper selection among various circuit breaker designs.

The emphasis on higher interrupting ratings, current limiting, and series ratings have impacted the short-time current ratings of circuit breakers. This IEEE Presentation provides the interrupting capacity and short-time current ratings of molded-case circuit breakers, insulated-case circuit breakers, and low-voltage power circuit breakers and their effect on time-current coordination. It will likewise review resistive and reactive X/R ratios and explain the short-time current and instantaneous trip characteristics of microprocessor-based trip units.

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