PaulEngr wrote:
How long can the screws for mounting/changing equipment in an MCC bucket be?
They can be as long as whatever the local hardware store stocks in the right thread size.
In all seriousness, that level of prescriptive design detail is probably not going to be in the equipment standards. The reference to 1" clearance, or the ability to pass certain DC and AC high potential tests is probably all we're going to find.
If you're talking about the machine screws used to mount equipment to the back panel of the MCC bucket, we could speculate that manufacturers would want to use one size of screw to mount each of the common components, so the length would be selected for the thickest mounting base of any component that is in the MCC's UL file as a standard component.
This is is similar to questions about clearance between MV components in equipment. There are various tables and rules of thumb available, however the right answer for manufactured equipment is whatever distance the manufacturer can use to pass the BIL tests.