Abstract: This paper introduced some problems of single-breakpoint moulded case circuit breaker in UL 489 high fault current test,and compared the judgment and external conditions of UL 489 and GB 14048.2 disconnection and its post-test,and analyzed single breakpoint for double breakpoint in the difference between the outgassing and the arc extinguishing.The conclusions obtained can provide a basis for the single-breakpoint moulded case circuit breaker to be used in UL 489.

Key words: single breakpoint moulded case circuit breaker, UL 489, high fault current, simulation design