Circuit-breaker ratings: weighing high interrupting capacity and short-time current ratings

This article discusses the interrupting-capacity (IC) rating and short-time current ratings of molded-case circuit breakers (MCCB), insulated-case circuit breakers (ICCBs), and low-voltage power circuit breakers (LVPCBs) and their effect on time-current coordination. Resistive and reactive X/R ratios are reviewed and the short-time current and instantaneous trip characteristics of microprocessor-based trip units are explained in this paper.