Isnt metal also thermally conductive as well as electricaly? Sounds like some sort of sleeve like iwire posted would be better for the purpose. Even a big gapping hole and a can of foam would be better IMO.
Also heres an interesting code and kinda funny when you see why its there, or not too funny depending on the situation. 300.7
Funny one: Jelly jar light filled with water.
Not funny: Rotted out disconnect falls apart when the AC mech LOTO's his switch, and and finds that it only partialy opens as it falls apart inside from rust.
