Utilization categories The utilization category of a circuit-breaker shall be stated with reference to whether or not it is specifically intended for selectivity by means of an intentional time delay with respect to other circuit-breakers in series on the load side, under short-circuit conditions (Table 4 IEC 60947-2). Category A - Circuit-breakers not specifically intended for selectivity under short-circuit conditions with respect to other short-circuit protective devices in series on the load side, i.e. without a short-time withstand current rating. Category B - Circuit-breakers specifically intended for selectivity under shortcircuit conditions with respect to other short-circuit protective devices in series on the load side, i.e. with and intentional short-time delay provided for selectivity under short-circuit conditions. Such circuit-breakers have a short-time withstand current rating. A circuit-breaker is classified in category B if its Icw is higher than (Table 3 IEC 60947-2): 12·In or 5 kA, whichever is the greater for In ≤ 2500A 30 kA for In > 2500A Electrical and mechanical durability Mechanical durability The mechanical durability of an apparatus is expressed by the number of no-load operating cycles (each operating cycle consists of one closing and opening operation) which can be effected before it becomes necessary to service or replace any of its mechanical parts (however, normal maintenance may be permitted). Electrical durability The electrical durability of an apparatus is expressed by the number of on-load operating cycles and gives the contact resistance to electrical wear under the service conditions stated in the relevant product Standard.

使用类别
断路器的使用类别应参考
无论是否通过故意的方式专门用于选择性
负载侧串联其他断路器的延时
短路条件（表4 IEC 60947-2）。
A类-非专用于以下情况下选择性的断路器
与其他短路保护装置相关的短路条件
负载侧串联，即没有短时耐受电流额定值。
B类——专门用于在短路条件下对串联的其他短路保护装置进行选择性的断路器
在负载侧，即在短路条件下，为选择性提供故意的短时延迟。这种断路器的时间很短
承受额定电流。
如果断路器的Icw高于IEC表3，则将其归类为B类
60947-2):
12英寸或5千安，以英寸中较大者为准≤ 2500A
大于2500A时为30kA
电气和机械耐久性
机械耐久性
仪器的机械耐久性是用仪器的数量来表示的
空载运行循环（每个运行循环包括一个关闭和关闭
（打开操作）在必要时
维修或更换其任何机械部件（但是，正常维护
可能是允许的）。
电气耐久性
设备的电气耐久性由负载的数量表示
工作循环，并在
相关产品标准中规定的使用条件。