How does a circuit breaker achieve short-circuit protection?

   The breaking capacity of a circuit breaker refers to the ability of the circuit breaker to safely cut off the fault current (different from the rated current). It is usually divided into limit breaking capacity Icu and operation breaking capacity Ics.

Icu refers to a certain test parameters (voltage, short-circuit current, power factor) under certain conditions, after a certain test program, can be connected, break the short-circuit current, after this pass, no longer continue to carry its rated current breaking capacity.

Ics refers to the short-circuit current that can be connected and broken under certain test parameters (voltage, short-circuit current and power factor) and by certain test procedures, and after this pass, it will continue to carry its rated current breaking capacity.

Simply put, a circuit breaker on the line fault current exceeds its limit breaking capacity, then this circuit breaker can no longer be used. While exceeding its operational breaking capacity, it can continue to be used after reset.

What is the breaking capacity of a circuit breaker?

The higher breaking capacity of a circuit breaker is, of course, the better, but the higher the breaking capacity, the more expensive it is. Combined with the actual cost-effective, usually 50KA to meet the use of many low-voltage lines, special occasions can be considered larger breaking capacity, such as 100KA breaking capacity.

Breaking capacity of 35KA, 50KA, 60KA, 80KA and other specifications, and the domestic miniature circuit breaker its limit short circuit capacity is generally between 4-6KA, and breaking reliability is not high.

If ICU=50KA, then when 50KA fault current occurs in the circuit, the circuit breaker can safely cut off the circuit without contact bonding, explosion, etc., but the circuit breaker with ultimate short-circuit breaking capacity can not be used again. If IUS = 50KA, when a 50KA fault current occurs, the circuit breaker can safely cut off the circuit, and can be used again when the fault is removed, but of course it is best to replace the circuit breaker.

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

Is the breaking capacity of the circuit breaker the bigger the better, that's for sure. The larger the breaking capacity, the higher the safety. For example, when the selection of ICU for 35KA, if the line short-circuit current of 20KA for the timely safety cut-off; but if the ICU for 20KA, the short-circuit current of 35KA can not be disconnected. Although the greater the breaking capacity the better, but the higher the price will be, or according to their own use in the premise of ensuring adequate safety, the economic choice of the right circuit breaker.