Abstract: In order to achieve overload and instantaneous characteristics,the small size two-breakers moulded case circuit breaker (MCCB) uses the direct heating bimetal sheet and solenoid electromagnet release device,but the structure of the release device can withstand less energy.By increasing the internal resistance,the current and energy of short circuit breaking can be reduced,and the high short circuit breaking capacity can be realized in the small size section.

Key words: moulded case circuit breaker (MCCB), small size, two-breakers, short circuit breaking