You’ll want to call the power company, as only they will know the setbacks required and, yes, it is based on how much electricity goes throught the lines. You are also correct that OSHA has certain requirements of how far from power lines people have to be to service a sign, and it is also based on how big the lines are. I would start with the power company, and they may also know the OSHA rules – if not, call OSHA direct or research it on-line.