I have come across 2 incidents that come to mind without thinking. One was I was working in a drop cieling and found about 78vac from grid to a ground. Found the problem was someone installed new lights to some old rag wire that had no ground, only a hot and nuetral. Installed a new conduit run with a ground and that took care of that problem. The other incident was on a work bench row about 40 ft long with approx 15 circuits. (installed by a private contractor) The metal raceway that carried the wires inside to the duplexes mounted into the raceway. We discovered about 90vac on the outside of the raceway. After searching for a few hours, we found the contractor had connected 2 of hi nuetrals together instead of to the pigtails for the duplexes. When the bench workers plugged in their test equipment, it didn't work, so they swapped the ground and the nuetral, this made there test equipment work, but the return voltage was going straight into the metal raceway because the duplexes were cut out of and into the raceway, by the factory I might add and UL approved. Connected the nuetral wires correctly and changed the plugs back to how they were before being tampered with and all was well. Those are a couple that come to mind.After 24 years I'm sure there are more, but thats all I remember for now