The most commonly used circuit breaker protection to achieve selective short circuit protection is the short delay protection, note the following:

1. minimize the delay time in the premise to meet the selectivity, the delay time of the circuit breaker should be shortened as much as possible . Because During the delay, the circuit breaker to withstand short-circuit current is large, which increases the manufacturing requirements of the circuit breaker, but also increases the cost. At the same time, the delay time is too long, the system will make a great voltage fluctuation is not conducive to the stable operation of the system. Thus, a short circuit should be carefully chosen short delay time, the delay time can not raise more.
2. reasonably determine the distribution stages using short delay selecting short circuit breakers in low voltage distribution systems, the delay time can be varied by changing the distribution stages, to reduce the distribution stages, the higher the delay time distribution It is also correspondingly reduced. In a specific distribution system, it should be based on the actual situation, a combination of factors to determine a reasonable number of stages of the power distribution system distribution.
3. The proper use of "natural" selective manner in the actual low voltage distribution systems, in a selective manner in all rare short circuit short delay, the entire "natural" rarely occur in a selective manner. Most low-voltage distribution system of mixed type in a selective manner, another embodiment of this combination is reasonable. The principle is to use "naturally" in a selective manner, and in a local system, especially in the middle and the end portions of the distribution, the use of "natural" in a selective manner.
4. When the circuit breaker when the circuit breaker of the three sections of an overcurrent protection, short delay and instantaneous short circuit protection snap three sections with protection, so that the lower short-circuit current difference is small, resulting in short-circuit failure occurs when the lower, upper and lower level circuit breaker will trip, can not guarantee the protection of selectivity. In this case only the instantaneous release snap superior protection, short delay only rely on the short-circuit protection. If a longer line failure, an instantaneous protection snap action, reduces the scope of protection, but it should snap into as transient protection, which is cut as soon as short-circuit fault within the scope of, and electrical circuit means to avoid being damaged, reduce economic losses caused by short-circuit fault.