Working class and operating mode of electric hoists

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It is common to see statements in manufacturer materials or on the Internet stating: (1) Working system: Jc M3. Question: What does Jc mean? Is it a term used for national standards or industry standards? (2) On Baidu online, there are job levels mentioned as M3 and M4; these job levels seem to be related to the working hours mentioned earlier. (3) There are also working systems online: Jc25%, heavy grade: Jc40%. According to the standard GB/T 3811-2008, there is no mention of a working system, nor is there any term Jc. Standardly, cranes are classified as follows: First: service class, U0-U9. Second: lifting capacity class, Q1-Q4. Third: overall machine service class (note: not duty cycle), A1-A8. Fourth: mechanism service class, M1-M8. Here comes the question: a) Where does the manufacturer’s classification system come from? Is there any correspondence with national standards? b) Are there any relevant descriptions in the ISO standards?