Thanks for all the suggestions, we ended up just cutting the conduit feeding the switch shorter and mounting an new switch alittle higher on the wall. Worked fine.
The overheating was because of oxidized terminals at the switch. Why the oxidized, I don't know but there are two 480V, 100A switches side by side, one for each of two boilers. And the other had the same problem last year and was replaced then. Wires were barely warm anywhere else, conduit nice and cool, and these things have been in service as is for 15 years.
Thanks again for the suggestions.
