The moulded case circuit breaker is an overload and short circuit maintenance appliance for low-voltage three-phase four-wire 220/380V circuits. Generally speaking, the separation is lower than that of the all-round circuit breaker and is therefore suitable for second, third and fourth level maintenance appliances for low voltage circuits and motors. In addition, because of the small number of generations of auxiliary contacts, they are not suitable for pre-operation of maintenance appliances or can only be used for one-time remote interception of circuits. Low voltage circuit breakers are not suitable for maintenance appliances with more than four stages from the main circuit breaker to the end. Otherwise, selectivity would be lost. The additional current In current rating is generally not adjusted. Additional currents Inm are available for each panel frame with a fixed rating difference for the additional current In of the circuit breaker. the following are 16A, 20A, 32A, 40A, 50A, 63A and 80A for Inm = 100A of type DZ20Y.

How to choose the circuit breaker for low voltage measurement level 2 and 3 also requires attention.

The short-circuit current Id of the distribution system; distribution lines or motors can be overloaded.

Frequent starting and reverse braking of high power heavy load motors.

There are many factors that are not conducive to safe and reliable operation, such as the temperature of the circuit breaker operating environment.

In general, after the additional current Inm of the circuit breaker casing is determined, In is suitable for selecting a class larger than the calculated current of the circuit and considering the overcurrent maintenance tripping time/current characteristics and selectivity of the additional current In of the upper and lower circuit breaker. The following functional indicators need to be confirmed when selecting plastic-cased low-voltage circuit breakers.

1. Additional voltage: AC240V, AC400V, AC415V, AC500V, AC690V, DC250V.

2. Additional current Inm of the housing of the molded case circuit breaker: the additional current level of each brand series is different, you need to specifically consult the material of the selected brand (such as Shanghai Taisi Electric), and then choose.

3.Additional current In of circuit breaker:The additional current level of each brand series is different and should be selected according to the load current or motor power of the distribution line shown and the technical data of the product to be selected.

4. Additional operating division before Ics: generally high level of circuit breaker product, the division is large. It must be selected according to the level of electrical load and the type of building and the financial burden in order to choose, must be divided, in order to be large as a quality commodity.

5. The additional marginal split is equivalent to Icu:Icu is 0.5-1 times the Ics. This means that it is no longer reused after passing the threshold split.

6. The additional short time withstand current withstands the overload current in 1s hours and does not affect the continuous use of the circuit breaker.

7. Number of poles: The number of poles varies from series to series. Usually 2-4 poles.

8. Overcurrent maintenance trip time/current characteristic curve: each series has a different characteristic curve, which is an important parameter, and one must think selectively about the upper and lower circuit breaker measures. There is an inverse relationship between the desorption point and the multiplier of the additional current overload measures, it is necessary to read and conclude carefully the technical data of the product to be screened.

9. Machine life: the number of machine life varies from series to series and is directly proportional to the level of quality of the circuit breaker, which is usually operated 3000-25000 times.

10. Electrical life number: the number of electrical life of each series is different, inversely proportional to the additional capacity of the plastic case circuit breaker, proportional to the level of quality of the circuit breaker, usually the number of operations is 1000-5000 times.

11. Plastic case circuit breaker device method: the circuit breaker is usually a fixed linear device.

12. Case volume scale: various series volume scale is completely different, need to investigate the various series sample materials. To check the number of auxiliary contacts of the circuit breaker, it must meet the needs of the distribution system.