Editing Overhead power line (section)

===Ground wires===
[[File:Al OC.jpg|thumb|Aluminum conductor crosslinked polyethylene insulation wire. It is used for 6600V power lines.]]
Overhead power lines are often equipped with a ground conductor (shield wire, static wire, or overhead earth wire). The ground conductor is usually grounded (earthed) at the top of the supporting structure, to minimize the likelihood of direct lightning strikes to the phase conductors.<ref>{{cite book|title=The Art and Science of Lightning Protection| isbn=9780521878111 |url=https://books.google.com/books?id=KO7fVcqispQC&pg=PA205 | last1=Uman | first1=Martin A. | date=24 January 2008 | publisher=Cambridge University Press }}</ref> In circuits with [[earthed neutral]], it also serves as a parallel path with the earth for fault currents. Very high-voltage transmission lines may have two ground conductors. These are either at the outermost ends of the highest cross beam, at two V-shaped mast points, or at a separate cross arm. Older lines may use [[surge arrester]]s every few spans in place of a shield wire; this configuration is typically found in the more rural areas of the United States. By protecting the line from lightning, the design of apparatus in substations is simplified due to lower stress on insulation. Shield wires on transmission lines may include optical fibers ([[optical ground wire]]s/OPGW), used for communication and control of the power system.

[[File:Fenno-Skan HVDC power line.jpg|thumb|HVDC Fenno-Skan with ground wires used as electrode line]]
At some HVDC converter stations, the ground wire is used also as the electrode line to connect to a distant grounding electrode. This allows the HVDC system to use the earth as one conductor. The ground conductor is mounted on small insulators bridged by lightning arrestors above the phase conductors. The insulation prevents electrochemical corrosion of the pylon.

Medium-voltage distribution lines may also use one or two shield wires, or may have the grounded conductor strung below the phase conductors to provide some measure of protection against tall vehicles or equipment touching the energized line, as well as to provide a neutral line in Wye wired systems.

On some power lines for very high voltages in the former Soviet Union, the ground wire is used for [[Power-line communication|PLC]] systems and mounted on insulators at the pylons.