mechanical oscillation of the lines that could be induced by mechanical vibration most likely that caused by wind. Without them its possible for a standing wave to become established that grows in magnitude and destroys the line or the tower. Arcing horns Arcing horns are sometimes added to the ends of the insulators in areas where voltage surges may occur. These may be caused by either lightning strikes or in switching operations. They protect power line insulators from damage due to arcing. They can be seen as rounded metal pipework at either end of the insulator and provide a path to earth in extreme circumstances without damaging the insulator. Physical security Towers will have a level of physical security to prevent members of the public or climbing animals from ascending them. This may take the form of a security fence or climbing baffles added to the supporting legs. Some countries require that lattice steel towers be equipped with a barbed wire barrier approximately above ground in order to deter unauthorized climbing. Such barriers can often be found on towers close to roads or other areas with easy public access, even where there is not a legal requirement. In the United Kingdom, all such towers are fitted with barbed wire. Other features Some electricity pylons, especially for voltages above 100 kV, carry transmission antennas. In most cases these are cellphone antennas and antennas for radio relay links adjoined with them, but it is also possible that antennas of radio relay systems of power companies or antenna for small broadcasting transmitters in the VHF-/UHF-range are installed. The northern tower of Elbekreuzung 1 carries in a height of 30 metres a radar station for monitoring ship traffic on Elbe river on its structure. The Tower 93 of Facility 4101, a strainer at Hürth south of Cologne, Germany carried from 1977 to 2010 a public observation deck, which was accessible by a staircase. Notable electricity transmission towers The following electricity transmission towers are notable due to their enormous height, unusual design, unusual construction site or their use in artworks. Bold type denotes structure which was at one time the tallest transmission tower(s) in the world. See also Architectural engineering List of high voltage underground and submarine cables List of spans Utility pole Stobie pole Live-line working References External links Electricity pylons in Hungary Pylon Appreciation Society Flash Bristow's pylon photo gallery and pylon FAQ