High-voltage transmission lines carry electricity from switchyards to local power grids, substations and other facilities. Transmission lines are designed to carry high voltages in order to minimize the energy loss that naturally occurs over long distances. Most of these lines span between tall transmission towers, while a small number are underground.
Overhead transmission lines are not insulated, and contacting them is dangerous. The coating on power lines is designed for protection from the weather and will not prevent electrical shock. Even approaching the lines with aerial equipment or extinguishing agents can cause electrical arcing. This is why transmission line emergencies require large safety clearances as well as unique response tactics.