Don't even go close to a downed HV or MV line. Step potential!
Just because it's not making sparks on the ground, there is no guarantee the line is dead and even if it is dead, there is no guarantee that it will remain so.
As I understand the original question, you are thinking of an ungrounded system. At first sight, it seems you could get away without getting shocked. But to detect a fault there has to be a current. The utility may to have a resistance ground which allows a small current to flow back to "sound the alarm". You don't want to be part of this circuit. In addition, there are unintentionally grounds along the line. I'm sure Bjarney, Trumpy and Scott35 know more about these things.
