Current limiting effects charts-a valuable engineering tool

The predominant engineering tool that allows the designer to evaluate short circuit protection levels is the current limiting effect chart. The author discusses the chart, and electrical system parameters than can affect the let-through values of current limiting fuses, and application considerations of how the let-through values are compared to the short circuit withstand ratings of static components such as wire, cable, bus structure, and motor starters. It is noted that protection of circuit breakers which exhibit current limiting characteristics requires additional analysis. The use of current limiting effect charts alone will not provide enough data to engineer protection of these types of breakers. The protection of circuit breakers which exhibit current limiting characteristics with current limiting fuses is addressed.<>