Moulded case circuit breakers are the most widely used protective appliances in our daily lives. When selecting and using them, a poor understanding of their technical capabilities and the conditions of the environment in which they are used can often lead to waste and frequent accidents. So, are there specific methods and considerations when selecting a moulded case circuit breaker?

一.Scope of application and use of moulded case circuit breakers

Moulded case circuit breakers are widely used in power distribution systems with rated voltage 690V, frequency 50/60Hz, rated current 16~1600a and transformers, motors, capacitors and other protection equipment. The moulded case circuit breaker mainly distributes power and protects each branch circuit and electrical equipment from overload, short circuit, leakage point and undervoltage, and can also be used for frequent conversion of lines and electrical equipment.

二.Selection methods for moulded case circuit breakers

Depending on the type of load, they are mainly divided into distribution systems and for motor protection.

According to the load capacity, choose a moulded case circuit breaker with a rated current greater than the load operating current.

Selection based on short-circuit current: The rated operating short-circuit breaking capacity of a moulded-case circuit breaker is greater than the expected short-circuit current value of the line. The short-circuit breaking capacity of a moulded-case circuit breaker determines the reliability of the breaker, but there is no need to pursue high divisibility to avoid waste when line safety is assured.

Selection considerations for moulded case circuit breakers

1、Difference in breaking capacity

Case circuit breaker breaking capacity has two important indicators: rated operating short-circuit breaking capacity Ics (including the conditions specified in the prescribed experimental procedures, circuit breakers continue to carry the rated current capacity breaking capacity) and rated limit short-circuit breaking capacity Icu (including the rated limit short-circuit breaking capacity Icu ) the conditions specified in the prescribed experimental procedures, circuit breakers continue to carry the rated current capacity breaking capacity) The difference between the two is that the rated limit short-circuit breaking capacity means that after the circuit breaker breaks the three-phase short-circuit current of the pin, it can be run again to break the short-circuit current again, and whether it can be normally closed and broken in the future cannot be guaranteed. The rated operating short-circuit breaking capacity must be able to break normally several times even under the above circumstances.

2、The use of circuit breakers in conjunction with each other

The choice of single circuit breaker directly affects the overall auxiliary line and the choice of conductor cross-section. The choice of circuit breaker must be based on the overall structure of the system, moulded case circuit breakers can be eliminated by an adjacent, higher level circuit breaker in the event of a fault at any point in the line.