If you have a three phase delta going into a industrial building for example and one of the legs hits the housing of a panel or transformer, what completes the circuit to open a fuse? I know in residential single phase the current will go through the neutral and back to source or grounds rod if the soil has a low impedance. But, what about in the situation I first mentioned? Is that why they used to use corner grounded systems back in the day? Thanks hope I made sense...