content: The 'sheathing' on the poles has nothing to do with grounding. It's to keep woodpeckers out. The lowest voltage a structure like this would carry is 69kv 'sub-transmission' but this could easily be a 115-230kv +/- line.  Powerlines are built to specs designated by engineers based on several factors - none of which has anything to do with what a utility happens to have laying around.