I. Application Scope and Usage of Molded Case Circuit Breakers

Plastic case circuit breakers are widely used in distribution systems with rated voltage of 690V, frequency of 50/60Hz, rated current of 16-1600A or as protective devices for transformers, motors, capacitors, etc. Plastic case circuit breaker is mainly used to distribute electric energy, do overload, short circuit, leakage and under-voltage protection of branches and electrical equipment, and also can be used for the infrequent conversion of lines and electrical equipment.

II. Selection Method of Molded Case Circuit Breaker

According to the type of load: mainly divided into distribution system and motor protection.

According to the capacity of the load, the rated current of the plastic case circuit breaker is larger than the working current of the load.

According to the short circuit current selection: the rated short circuit breaking capacity of plastic case circuit breaker is greater than the expected short circuit current value of the line. The short-circuit breaking ability of plastic case circuit breaker determines the reliability of circuit breaker, but in the case of ensuring the safety of the circuit, it is not necessary to pursue high breaking ability blindly to cause waste.

Notices for Selection of Molded Case Circuit Breaker

1. The difference of breaking ability

There are two important indexes for the breaking capacity of plastic case circuit breaker: the rated operating short circuit breaking capacity Ics (the breaking capacity of the circuit breaker to continue carrying its rated current capacity according to the specified experimental procedures), and the rated limit short circuit breaking capacity Icu (the conditions specified in the specified experimental procedures, including circuit breakers). Continue to load its rated current capacity of the breaking capacity. The difference between the two is that the rated limit short-circuit breaking capacity refers to that the circuit breaker can run again after breaking the three-phase short-circuit current at the outlet end and break the short-circuit current once again. As for whether the short-circuit current can be connected and broken normally in the future, it is not guaranteed. However, the rated short-circuit breaking capacity needs to be able to break normally many times under the above circumstances.

2. Cooperative Use of Circuit Breakers

The selection of a single circuit breaker directly affects the selection of the overall parts, lines and conductor sections. Circuit breakers should be selected according to the overall composition of the system. In order to eliminate the faults at any point of the line, the adjacent upper circuit breaker can eliminate the faults.