Safe to cut vine wrapped around electric mains?
Responsibility for the service drop (the wire from the utility to your house) lies with the utility.  Generally the demarcation line is the splice between the service drop and the conductors leading up the mast.

Your electrical utility thus may be willing to clear these vines.

The wires are insulated, though you can't trust the insulation is perfect. The vines won't conduct enough electricity to matter.  But if you cut the vines they'll die and dry out, and be far harder to pry off the line.  Damage from the vines will at first be mechanical, as the weight of the vines especially if it's windy can be significant.

If you do clear the vines yourself, use a wooden ladder, wear electrician's insulating gloves, and gently unwrap the live vine without risking directly touching the insulated service drop wires.  If you see flaws in the insulation, call the power company right away.

http://inspectapedia.com/electric/Electrical_Service_Drop.php