An overhead line crossing (see Domain specific aliases) is the crossing of an obstacle (such as a traffic route, a river, a valley or a strait) by an overhead power line. The style of crossing depends on the local conditions and regulations at the time the power line is constructed. Overhead line crossings can sometimes require extensive construction and can also have operational issues. In such cases, those in charge of construction should consider whether a crossing of the obstacle would be better accomplished by an underground or submarine cable.
Domain specific aliases Several related terms are used in engineering, regulatory, and planning contexts. These terms are partly overlapping and may differ slightly in scope or emphasis. Term Typical context Scope Notes Overhead line crossing Power-engineering and infrastructure descriptions Overhead power lines crossing obstacles Describes a span where an overhead line passes over roads, railways, rivers, valleys, or other obstacles. Overhead power line crossing Technical reports, environmental assessments Same as above Explicitly specifies that the crossing involves an overhead power line rather than underground infrastructure. Power line crossing Regulations and infrastructure agreements Broader term often used in railway, road, or utility regulations for any electrical line crossing an infrastructure corridor. Transmission line crossing Electric-utility and grid-planning documentation High-voltage transmission lines Used when referring specifically to crossings by long-distance transmission lines rather than lower-voltage distribution lines. Span crossing Transmission-line engineering Individual spans of overhead lines Refers to a specific span that crosses an obstacle, such as a road-crossing span or river-crossing span. Utility crossing Transportation and civil-engineering contexts Any utility infrastructure Broad term covering crossings by utilities such as power lines, pipelines, or telecommunications cables across transportation corridors.
Crossings of roads and railway lines Overhead line crossings of roads, railway lines, and small- and medium-sized watercourses do not normally require special construction. However, in the first years building overhead line when crossing a railway line or a road, a scaffold under the line was required. Later in Germany and some other countries on each end of a powerline crossing of a state-operated railway, a dead-end tower was required, which can still be seen on some old power lines. For overhead line crossings of motorways the pylons must be rebuilt before they wear out, because these demand additional maintenance. If local conditions are appropriate, an overhead line can be implemented by way of a valley bridge. For example, the Koersch valley bridge near Esslingen, Germany carries the 110 kV, three-phase line of the EnBW AG with 2 circuits. Because of the danger of short circuits from falling objects, undercrossings are typically avoided.
Crossings of overhead lines at state borders
There is frequently an anchor pylon on each side of state borders, particularly if the lines on either side are operated by different companies. This setup reduces maintenance work, which would otherwise require direct coordination of workers on both sides of the border, and avoids possible authority problems associated with border crossings as much as possible.
Crossings of other overhead lines
At crossings of overhead lines by other overhead lines, the two lines must be kept at the necessary safety distances between the lines and the ground. As a rule, the line with the lower voltage passes under the line with higher voltage. Construction workers try to plan these crossings in such a way that their construction is as economical as possible. This is usually done by leaving the line that is crossed unchanged, if possible. Undercrossings of existing lines are often constructed in proximity to the line's pylons, since this can often be accomplished without raising the existing pylons, and while keeping the necessary safety distances between the ground and the other line.
In the course of undercrossings the pylon picture is frequently changed, and because of its small height it is preferable to create an arrangement with conductors on one level. Sometimes at such crossings there can be problems because of the maximum pylon height allowed for flight safety reasons. If it is not possible at a given location for the pylons of the upper line to be built at a necessary height, the line running below it will be rebuilt on smaller pylons or replaced with an underground cable.
A unique undercrossing of two powerlines can be found north of Kincardine at Scotland at 56°5'17"N 3°43'11"W. Here crosses the powerline Kincardine-Tealing two other lines. One of the two circuits of Kincardine-Tealing powerline crosses these lines on two small pylons and the other circuit via an underground cable.
Special crossings from overhead lines of other overhead lines
There are some crossings between two overhead powerlines, which are unique, either as both lines are of special type or the unique way of implementation