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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.

使用類別
斷路器的使用類別應(yīng)參考
無論是否通過故意的方式專門用于選擇性
負載側(cè)串聯(lián)其他斷路器的延時
短路條件（表4 IEC 60947-2）。
A類-非專用于以下情況下選擇性的斷路器
與其他短路保護裝置相關(guān)的短路條件
負載側(cè)串聯(lián)，即沒有短時耐受電流額定值。
B類——專門用于在短路條件下對串聯(lián)的其他短路保護裝置進行選擇性的斷路器
在負載側(cè)，即在短路條件下，為選擇性提供故意的短時延遲。這種斷路器的時間很短
承受額定電流。
如果斷路器的Icw高于IEC表3，則將其歸類為B類
60947-2):
12英寸或5千安，以英寸中較大者為準≤ 2500A
大于2500A時為30kA
電氣和機械耐久性
機械耐久性
儀器的機械耐久性是用儀器的數(shù)量來表示的
空載運行循環(huán)（每個運行循環(huán)包括一個關(guān)閉和關(guān)閉
（打開操作）在必要時
維修或更換其任何機械部件（但是，正常維護
可能是允許的）。
電氣耐久性
設(shè)備的電氣耐久性由負載的數(shù)量表示
工作循環(huán)，并在
相關(guān)產(chǎn)品標準中規(guī)定的使用條件。