a few years ago we were working on a section of 4000 amp 480 volt switchgear that blew up due to a line side phase to phase explosion. the vault bus stub was only about ten feet long with an elbow in it and came down and bolted to the back side of the switchgear's line side bus. from the damage we knew the failure was in this area. this gear is infrared yearly. we jumped the section out and had the building on line the next day. this allowed us to begin removal of the damaged line side stub. we could not find a problem until we began to remove the overhead bus stub section from the switchboard when we heard a piece of metal fall down thru the gear??? it was a four inch long piece of steel with a 1/2 inch tappped hole in the center. the inside retaining nut for the switchgear's lifting eye was never removed and we found others still in place held only by paint. the original installer may have thought they were welded in place? or maybe they should be?? in any case i thought i'd just mention it --- check them out - this was about a $250,000 problem and was g.e. gear.