Breaking capacity of circuit breaker is an important index of circuit breaker, which refers to the ability of circuit breaker to safely cut off fault current. It is generally divided into rated limit short-circuit breaking capacity ICU and rated operation short-circuit breaking capacity ICs. The breaking capacity has 35ka, 50kA, 60kA, 80kA and other specifications, while the short-circuit limiting capacity of domestic miniature circuit breakers is generally between 4-6ka, and the breaking reliability is not high.

假如ICU=50KA，那么当电路中发生50KA故障电流时，断路器可以安 全的切断电路，而不会发生触头粘接等状况，但发生限短路分断的断路器不可以再使用。而假如IUS=50KA，当发生50KA故障电流时，断路器可以安 全切断电路，在故障排除时可以再合闸使用，当然也是更换断路器。

If ICU = 50kA, then when 50kA fault current occurs in the circuit, the circuit breaker can safely cut off the circuit without contact bonding and other conditions, but the circuit breaker with limited short circuit breaking can no longer be used. And if IUS = 50kA, when 50kA fault current occurs, the circuit breaker can safely cut off the circuit, and it can be reclosed for use when troubleshooting. Of course, it is also to replace the circuit breaker.

选择断路器的一项重要原则就是断路器的限短路分断能力要大于线路的预期短路电流。无论哪种断路器，它的短路分断能力都大于或等于其运行短路分断能力。

An important principle in selecting circuit breakers is that the short-circuit breaking capacity of circuit breakers should be greater than the expected short-circuit current of lines. No matter what kind of circuit breaker, its short-circuit breaking capacity is greater than or equal to its operating short-circuit breaking capacity.

断路器的分断能力是否越大越好呢，那是肯定的。分断能力越大，安 全性越高。例如当选择ICU为35KA时，如果线路中短路电流为20KA时为及时安 全切断；但如果ICU为20KA，则短路电流为35KA时就无法断开了。虽然分断能力越大越好，但是价位也会越高，还是要根据自身使用情况在保证足够安 全的前提下，经济的选择合适的断路器。

It is certain that the greater the breaking capacity of the circuit breaker, the better. The greater the breaking capacity, the higher the safety. For example, when the ICU is 35ka, if the short circuit current in the line is 20KA, it is safe to cut off in time; However, if the ICU is 20KA, it cannot be disconnected when the short-circuit current is 35ka. Although the greater the breaking capacity, the better, but the price will also be higher, or according to their own use, in the premise of ensuring sufficient safety, the economic choice of the appropriate circuit breaker.