Moulded case circuit breaker (VCB) is widely used in low-voltage distribution industry, which is used to cut off or isolate the fault current within the normal and rated range to ensure the safety of lines and equipment. In addition, according to the requirements of China's technical code for safety of temporary electricity use on construction site, the temporary electricity circuit breaker on construction site must be transparent shell, which can clearly distinguish the on-off state of main contact, and the compliance circuit breaker must be pasted with the "AJ" sign issued by relevant safety departments.

塑壳断路器有多种附件可以加挂，如远程电动操作分合闸机构、分励线圈、辅助触点、报 警触点等。

Moulded case circuit breaker has a variety of accessories that can be hung, such as remote electric switching mechanism, shunt coil, auxiliary contact, alarm contact, etc.

电动操作机构选型时需注意配套断路器壳架电流，因为不同壳架电流的断路器外形尺寸还有分合闸机构的扭矩不同。

When selecting the type of electric operating mechanism, it is necessary to pay attention to the shell frame current of the matching circuit breaker, because the external dimensions of the circuit breaker with different shell frame current and the torque of the opening and closing mechanism are different.

塑壳断路器另一项重要性能指标是其额定短路分断能力，此项数值的高低直接影响断路器安全分断故障电流的能力，一般为25/35/50/65kA。我们实际选择过程中可以根据设计院图纸要求选用，无要求的可以根据经验计算回路预期短路电流值。断路器短路分断能力要大于回路预期短路电流。为节省成本，短路分断能力值够用就好。

Another important performance index of molded case circuit breaker is its rated short-circuit breaking capacity, which directly affects the safe breaking fault current capacity of the circuit breaker, generally 25 / 35 / 50 / 65ka. In the actual selection process, we can select according to the drawing requirements of the Design Institute, and if there are no requirements, we can calculate the expected short-circuit current value of the circuit according to experience. The short-circuit breaking capacity of the circuit breaker should be greater than the expected short-circuit current of the circuit. In order to save cost, the short circuit breaking capacity value is enough.

塑壳断路器可以做成带漏电保护功能，但是跟微型漏电断路器一般为30mA漏电动作电流不同，塑壳漏电断路器漏电动作电流多为100/300/500mA可调，因此可见，带漏电保护的塑壳断路器主要是保护下端设备或电缆漏电，而不是用来直接保护用电人员。此类断路器实际使用过程中有一弊端，就是一般这类断路器下端设备较多，施工人员接线过程中很容易失误将零线和地线弄混，而导致总开关漏保跳闸，这类问题查起故障点来非常费事儿

Moulded case circuit breaker can be made with leakage protection function, but it is different from miniature leakage circuit breaker which is generally 30mA leakage action current. The leakage action current of moulded case leakage circuit breaker is mostly 100 / 300 / 500mA adjustable. Therefore, it can be seen that moulded case circuit breaker with leakage protection is mainly used to protect the lower end equipment or cable leakage, rather than directly protect the power users. There is a drawback in the actual use of this kind of circuit breaker, that is, there are many devices at the lower end of this kind of circuit breaker, and it is easy for the construction personnel to mix the zero line and ground line in the wiring process, which leads to the main switch leakage protection trip. It is very difficult to find the fault point for this kind of problem