Moulded case circuit breakers are overload and short-circuit maintenance appliances for low-voltage three-phase, four-wire 220u002F 380V circuits. As their breakage is usually lower than that of a full-powered circuit breaker, they are suitable as second, third or fourth level maintenance devices for low-voltage circuits and motors. Due to the relatively small number of auxiliary contacts, they are not suitable for the active operation and maintenance of appliances or can only be used as a one-time remote open circuit. Low voltage circuit breakers for maintenance appliances are not suitable for more than four levels from the main circuit breaker to the end, otherwise selectivity is lost. The additional currents in the current levels are usually not adjusted and the additional current Inm for each case frame is matched to the additional current INM of the circuit breaker with fixed level difference. Take for example DZ20Y Inm = 100 A. In has eight levels: 16 A, 20 A, 32 A, 40 A, 50 A, 63 A, 80 A and 100 A, but INM In IB must be known.

Low voltage measurement of second and third level circuit breakers and how to make the selection also requires more attention to.

Distribution system short-circuit currents Id; distribution line or motor capacity overloads.

High power heavy motors with variable frequency start and reverse braking ;

Breaker operating ambient temperature and many other factors that are not conducive to safe and reliable operation.

Usually through the circuit breaker shell frame additional working current Inm determined after In suitable than the line for accounting system current to choose a large level, but also fully consider the enterprise up and down the circuit breaker needs additional current In overcurrent can maintain the time/current control characteristics and selectivity of the decoupling device, in the plastic case low-voltage circuit breaker selection, should check the functional analysis indicators are, as follows：

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

2. Circuit breaker additional current: Different brands have different levels of additional current, you must read the brand (e.g. Shanghai Taisi Electric) before using to select the material.

3. Additional current input of the circuit breaker: the additional current level of each brand series is different, so the selection must be made according to the load current or motor power of the distribution line depicted and the technical data of the selected product.

4. additional operating breaking capacity Ics: usually circuit breaker products of different levels of high that breaking capacity, need to be based on the enterprise power supply system load capacity level and building type and funds can afford such a final selection, to breaking capacity large for quality products.

5. additional limit breaking capacity Icu: ICU is equal to 0.5-1 times of Ics, that is, the limit breaking after no longer used.

6. Ultra short-term withstand current ICW: Overload current withstand 1 second, does not affect the continuous operation of the circuit breaker.

7. Number of poles: the number of poles varies for each series, generally 2-4 poles.

8. Overcurrent for maintenance of the striker moment / current characteristic change curve: each series of products characteristic curve through different, which is our depiction of staff can be selective to the upper and lower level circuit breaker initiatives need to be managed important technical parameters to consider. The moment of release and additional current overload initiative multiplier relationship between the inverse link, it is necessary to read in detail Desired product skills study material before determining.

9. mechanical life: the number of mechanical life of each series of products is different, proportional to the quality level of the circuit breaker, usually the number of operations is 3000-25000 times.

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

11. Plastic case circuit breaker device mode: the circuit breaker is usually fixed straight device.

12. Case volume different scale: various product series volume scale thoroughly different, need to check the various education series product research sample data materials. Check the number of auxiliary contacts of the circuit breaker, should be satisfied with the development of the distribution management system needs.