1) The coordination between circuit breakers should consider the instantaneous tripping action value of the higher-level circuit breaker, which should be greater than the maximum expected short-circuit current at the output end of the lower level circuit breaker. If the impedance value difference of the circuit components is small when the two levels of circuit breakers are short circuited, and the short-circuit current value difference is not significant, then the higher-level circuit breaker can choose a tripping device with short delay.

2) When the short-circuit current of the current limiting circuit breaker is greater than or equal to its instantaneous trip setting value, it will trip within a few milliseconds, so it is not suitable to use circuit breakers to achieve selective protection requirements for lower level protective electrical appliances.

3) When the time limit of a circuit breaker with short delay is set at the maximum delay, its breaking capacity decreases. Therefore, in selective protection circuits, the short delay breaking capacity of the selected circuit breaker should meet the requirements.

4) It should also be considered that the short-circuit delay return characteristic of the higher-level circuit breaker should not intersect with the action characteristic time curve of the lower level circuit breaker, and the short-circuit delay characteristic curve should not intersect with the instantaneous characteristic curve.

5) When using circuit breakers in conjunction with fuses, consideration should be given to the coordination between upper and lower levels. The ampere second characteristic curve of the circuit breaker should be compared with that of the fuse to ensure protection selectivity in the event of short-circuit current.

6) When using circuit breakers for the protection of distribution lines, it is advisable to choose circuit breakers with long delay overcurrent release devices. When a single-phase grounding short circuit occurs at the end of the line, the short-circuit current should not be less than 1.5 times the instantaneous or short delay overcurrent release device setting current of the circuit breaker.