why does the power company use helicopters to service the repair lines instead of trucks with tall cranes?
High-tension lines operate at hundreds of thousands, or millions, of volts. At this potential, electricity can jump through several feet of air to reach a path to ground. This pretty much rules out using trucks, because it would be prohibitively expensive or impossible to build a crane out of entirely non-conductive materials. A helicopter is electrically isolated from the ground, so it's less difficult to drop a technician off and let him hang from the line itself while working. (It is still necessary for the technician to use a wand to bring the helicopter to the line's potential before starting work, because of the capacitance of the helicopter's body.) They could of course use a truck to service the lines if the power was disconnected, but the cost of shutting down service to an entire region of the country exceeds the operating cost of a helicopter.
