It is a protection method which only trips the related circuit breaker and other fault-free circuit does not trip and continues power supply in the event of short circuit fault. In details, only a branch circuit breaker trips and main circuit breaker and other branch circuit breakers does not trip. Breaking capacity ensuring selective breaking method is generally up to instantaneous tripping current of a main circuit breaker, but it is possible to get selective breaking capacity more bigger if you use a circuit breaker with great current limiting performance on downstream (branch) and make passing current on main circuit breaker more smaller. Moreover, an electronic circuit breaker and air circuit breaker with generally high instantaneous tripping current have the effect making selective breaking capacity bigger.