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Glossary for British pylons and high-voltage power lines



Technical terms

All-Aluminium Alloy Conductor (conductor type); each type is named after a type of tree
Aluminium Conductor Steel Reinforced (conductor type); each type is named after a type of mammal
Aluminium Alloy Conductor Steel Reinforced (conductor type)
Aluminium Conductor Alloy Reinforced (conductor type)
Cable sealing end (“sealing end”)
Steel-cored aluminium; an older term for ACSR
Sealing end compound
Sealing end platform
Standard height
Standard height


Balfour Beatty
British Electricity Boards Specifications
Official abbreviation of British Insulated Callender’s Cables
Blaw Knox
British Electricity Authority (1947–1955)
“Central Electricity” (but see also 1930s electricity schemes below)
Central Electricity Board (1927–1948)
Central Electricity Generating Board (1958 until privatisation in the 1990s)
J L Eve Construction
Kennedy & Donkin
Merz & McLellan
South Western Electricity (but see 1930s electricity schemes also below)

1930s electricity schemes

The following prefixes can be found on tower designations, indicating the applicable region of Great Britain.

Central England
Central Scotland
East England
Mid East England
North East England
North West England and North Wales
South East England
South Scotland
South West England and South Wales


Angle tower
A form of tower that has sufficient strength and stability to withstand the diagonal pull from the conductors where the route changes direction. Also known as an angle tower, deviation towers are tension towers. The width at the base increase with supported deviation angle, and the crossarms generally become less symmetrical: longer ot the outside of the angle and shorter on the inside. Changes in elevation are generally accommodated by suspension towers.
Contrary to expectation, “cable” refers to an underground cable (buried power lines). Overhead cables on towers and poles are “conductors” and the earth cable is the “earthwire” or “earth wire” (even though it is a cable).
Any of the cables that are strung from a transmission tower that carry power. For 132 kV there are normally three or six conductors depending on whether the tower is single or double circuit. For higher voltages each phase is typically a bundle of two to four conductors held apart by spacers, so an L6 tower often has 18 or 24 conductors grouped into six bundles of three or four conductors, on bundle per phase. Also known as “line conductors” and “phase conductors”.
Conductor clashing
This is where the cables from different circuits or phases collide under strong winds. To minimise this, many double-circuit towers have middle crossarms that are significantly wider than the top and bottom crossarms.
Any of the arms on a tower that support the conductors
A change in compass direction (rather than elevation) of the route that the overhead lines follow. For example, an L4 D90 tower is used route the wires around the Crawley Green Football Club in Luton, with the wires taking a right-angled turn at the corner of the grounds. These direction changes occur at angle towers (deviation towers), where the incoming and outgoing cables face different compass directions; the aforementioned change in direction in Luton uses a D90 tower that allows up to a 90° change in direction.
Deviation tower
Another term for angle tower.
Diamond crossing
This is a crossing between two lines, where one line is split onto two gantries and routed around a tower of the other line. Not to be confused with diamond crossings on railways.
A cable connecting one of the phase cables on the tower to ground-level equipment, found at sealing end compounds, sealing end platforms and substations.
Earthwire shade
The protection offered by the earthwire against lighting strikes hitting the conductors below. A narrower angle is better, thus the earthwire should be significantly higher than the top crossarm.
Intermediate tower
Another name for suspension tower.
Line conductor
See conductor.
Line tower
Another name for suspension tower.
Phase conductor
See conductor.
A single run of conductor cable, terminated at each end by tension towers (terminal towers, angle towers or section towers). Within a section, all towers are tension towers.
Section tower
An angle tower used in straight line configuration to terminate an adjacent pair of sections; found when a straight line run exceeds the conductor cable length.
Although “span” may suggest width (as in, crossarm width, or width between adjacent conductors), with transmission lines it denotes the distance between towers or the connections between towers. The standard span was 1000 feet, i.e. each tower was around 1000 feet away from the next one. The length of a span is determined by various factors including land availability, tower positioning, changes in elevation and changes in direction. It can be possible to exceed the span limit between a pair of towers, although this will reduce the limit of the next span.
Suspension tower
A tower where the conductors are suspended from vertical strings of insulators. Also referred to as a straight line tower, intermediate tower or line tower, suspension towers are contrasted with deviation towers by not allowing a change in line direction. (With that said, older designs of suspension tower do allow deviation up to 2° or 10° depending on the type.)
Tension tower
A tower where the conductors are attached to nearly-horizontal strings of insulators under tension. See deviation tower, terminal tower.
Terminal tower
A tower where the line comes to an end and is terminated onto ground-level equipment.
The industry term for pylon, even though the term pylon was specifically chosen for steel lattice transmission towers!