I always get asked "whats a good source of xxxxx parts" for hobby use, and usually it comes down to control cabinets, and if you can get them cheap at a scrap yard or surplus store, its a great way to save thousands on parts for hobby use!.
Of course, watch out for burned terminals, wet or rusty parts, surge damage, and if in doubt, throw it in the trash or test it well at the very least!.
Using unknown parts in industry however has its own liabilities because its not just your ass on the line, always check with the boss before swapping out used parts. Likewise do not make entry to a working panel without permission/qualification!. this video is mainly aimed at hobbyists with prior knowledge of electrical engineering.
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