Heres one for you to ponder. Had a call from a friend who owns a welding shop. He was working on a free standing metal table, ( on concrete ) ...and had the work clamp attached to the table. His overhead crane base, was approx 4 to 5 feet away. The tip of the rod came into contact with the chain hanging from the crane, and he got a good spark. Kind of questioning how this would happen, as there is no direct metal contact between the table and the crane. So next time i went over there, and brought my megger. Attached one lead to the table and the other to the bolt on the base of the crane....pressed test, and had a dead short. Just as if the table was connected to the crane with a piece of metal. Like WTH?? I walked around the table several times to be sure we didnt miss anything. The megger is working fine, no issues there. Anyone seen anything like this??? He said that has never happened in the years before this. After discussing with some fellow sparkies, the only thing that makes sense, is that possibly the concrete may have a thin film of metal shavings across the surface and into the small cracks, etc....that it actually provides continuity across the floor. The rebar in the floor is about 8 inches down.....so that shouldnt be a factor. Next time im in the area, im going to bring a magnetic sweep and see if this makes any sort of a difference. I thought it may have some sort of a reading....but at 1kv it was 0..... and 500...the same. Any feedback would be welcome......cheers!!!