L8
Caveat
Due to the limits of the available data, details on the pylon pages are incomplete and in places inaccurate or incorrect. Pages typically only cover standard tower types and common variants. This information is provided for enthusiasts and those of a curious mind and is not authoritative. Additional source material is welcome, in particular drawings. Most data and illustrations provided are sourced from industry-related material. See the sources page for a list of sources and the series page for a list of series.
Contents
Overview
L8 is a UK electricity pylon (steel lattice transmission tower) series.
L8 comes in at least two forms: tall (46 metre) 400 kV towers, and shorter and slimmer 275 kV towers. The 275 kV towers seem to have an “R” prefix to the tower type. L8 RD looks like a cross between L3 and L12, and can be found on the new 275 kV line between Dounreay Substation (58.576° N 3.754° W) to Spittal Substation (58.480° N 3.452° W) via Thurso South Substation (58.5647° N 3.513° W). This 275 kV line replaced an older 132 kV line (PL16) that has since been removed but is still shown on Open Infrastructure Map.
Just as with L6, and unlike L2 that it is said to have replaced, L8 does not have a separate D10 type. Instead, there are separate foundation dimensions for the 0–10° and 10–30° versions of the D30 tower.
Single-circuit-adapted L8 can be seen on the short 2.3 mile run (2 miles as the crow flies) that connects the 819 MW Sutton Bridge Power Station (52.757° N 0.192° E) to the nearby Walpole Substation. National Grid’s terminology page claims that “a 400 kV National Grid circuit may carry 1 kA in each of its three phases, thus transmitting a power of 700 MW”; possibly this L8 line has higher rated conductors, as the power station is rated slightly higher than this. The 0° towers on this line appear to be standard D towers with the bottom crossarm and half of the top crossarm deleted; this is the same adaptation as seen with L4(m). The deviation towers are less clear; from what little can be seen of them, there is a suggestion that they are customised for lower height.
L8 is said to be a replacement for L2, although this is yet to be confirmed from official literature. Like L2, there are 15° and 45° earthwire changeover (EC/EWCO) types. Chart 35/8744 covering L8(c) indicates that all towers are to Blaw-Knox design.
L8(c) is the metric conversion of L8. The height adaptations are thus listed in both imperial and metric, e.g. E24 and E7.3.
General data
Some height information is given in [East Coast 400 kV EIA] for “L8”. The tower heights in that material are rounded to the nearest metre; analysis would imply however that the height extensions and reductions are in feet. It thus appears that height adaptations were in multiples of four feet, and that the figures relate to the original Imperial L8 instead of the metric L8(c).
Known subtypes |
L8 L8(c) (metric conversion) |
---|---|
Height (straight line tower) |
46.4 m (400 kV) ca. 40 m (275 kV) |
Voltage | 400 kV, 275 kV |
Dates back to | 1966 (specification) |
Conductors | Twin |
Known heights (400 kV) |
M24, M12, STD (all) E12, E24, E36, E48, E60 (not SF60) Additional options for D See table below for more details |
Details on the 275 kV version are very limited. The “L8” type given in [Dounreay to Mybster]—clearly an L8 RD variant—is shown with a height of 33123 mm and a base width of 5486 mm; the height is described thus:
The towers used for the 275 kV OHL will vary in height between 32m and 52m to accommodate changes in topography and where the line crosses roads and rivers, although the height will generally be in the region of 40m.
The L8 RD M4.9 diagram comes from [NeSTS SSEN003]. No height is given for this tower, so it was scaled using the diagram in [Dounreay to Mybster], through which it comes out at around 35.6 m. Adding the 4.9 m from the height reduction gives 40.5 m, very close to the implied size of the standard tower at 40 m.
Designation | Phase | Earthwire | Voltages used | Per | |||||
---|---|---|---|---|---|---|---|---|---|
Twin 400 mm² ACSR (Zebra) | 175 mm² ACSR (Lynx) | 400 kV | 35/8744 (1975 or 1977) |
Suffix | Tower type | ||||||||
---|---|---|---|---|---|---|---|---|---|
Imperial | Metric | D | D30 | D60 | D90 | DT | DJT | ST | SF60 |
M24 | M7.3 | ✓ | ✓ | ✓ | ✓ | ✓ | ✓ | ✓ | ✓ |
M16 | † | ✓ | |||||||
M12 | M3.7 | ✓ | ✓ | ✓ | ✓ | ✓ | ✓ | ✓ | ✓ |
M8 | M2.4 | ✓ | |||||||
M4 | † | ✓ | |||||||
STD | ✓ | ✓ | ✓ | ✓ | ✓ | ✓ | ✓ | ✓ | |
E4 | † | ✓ | |||||||
E8 | † | ✓ | |||||||
E12 | E3.7 | ✓ | ✓ | ✓ | ✓ | ✓ | ✓ | ✓ | |
E16 | † | ✓ | |||||||
E20 | † | ✓ | |||||||
E24 | E7.3 | ✓ | ✓ | ✓ | ✓ | ✓ | ✓ | ✓ | |
E28 | E8.5 | ✓ | |||||||
E36 | E11.0 | ✓ | ✓ | ✓ | ✓ | ✓ | ✓ | ✓ | |
E48 | E14.6 | ✓ | ✓ | ✓ | ✓ | ✓ | ✓ | ✓ | |
E52 | E15.9 | ✓ | |||||||
E60 | E18.3 | ✓ | ✓ | ✓ | ✓ | ✓ | ✓ | ✓ | |
E90 | E27.4 | ✓ | |||||||
E120 | E36.6 | ✓ | |||||||
E150 | E45.7 | ✓ |
“M” (minus) figures are reductions in height, and “E” figures are extensions in height. The metric suffixes correspond to L8(c) metric conversion.
Entries marked † are from [East Coast 400 kV EIA] and are given for “L8”. The remaining data is from L8(c) drawing 35/8744.
Tower forms
The following diagrams are shown to scale at 12 pixels per metre. First, the full-size 400 kV towers:
There are two versions of the SF60 tower, for 0–20° and 20–60° deviation ranges.
Middle phase:
0°–20° deviation use centre line of tower
20–60° deviation offset 1.905 m and long extension crossarm
The smaller 275 kV towers:
The third image is taken to be M7.3 as it is around 2.5 m taller than M4.9, in line with the expected 2.438 m difference (8 feet). The standard height (STD) drawing is a combination of the D STD and RD M7.3 and drawings. In practice, it seems that these towers tend to be built in M sizes, possibly because at 275 kV the voltage is lower than the 400 kV design voltage of L8 and thus the full height is not necessary.
Like L4(m), L8 has been adapted into single-circuit form; as with L4(m), the designations are not known and those given below are only suggestions:
Tower details
Crossarm width is the total width across the widest arms. Base width is back-to-back of the stubs at ground level; dimension over concrete at ground level is around 400–500 mm greater.
There is no D10 type; there are instead 0–10° and 10–30° variants of the D30 that differ in the dimensions of the foundations, sharing the same tower design and crossarm lengths.
Type | Source | Height | Base width | Crossarm width | Weight |
---|---|---|---|---|---|
L8(c) D STD | 35/8744 | 46.4 m | 7.5 m | 17.1 m | 13.0 tonnes |
L8(c) D30 STD | 35/8744 | 43.8 m | 9.6 m | 17.5 m | 21.0 tonnes |
L8(c) D60 STD | 35/8744 | 44.5 m | 10.8 m | 18.2 m | 24.0 tonnes |
L8(c) D90 STD | 35/8744 | 49.4 m | 16.2 m | 21.8 m | 34.3 tonnes |
L8(c) DT STD | 35/8744 | 46.3 m | 10.8 m | 19.5 m (standard width) 25.6 m (extended) |
38.1 tonnes (standard) |
L8(c) DJT STD | 35/8744 | 48.2 m | 14.2 m | 26.1 m (standard width) 31.1 m (extended) |
43.9 tonnes (standard) |
L8(c) ST STD | 35/8744 | 44.3 m | 9.6 m | 22.1 tonnes | |
L8(c) SF60 STD | 35/8744 | 21.1 m | 11.0 × 6.3 m | 19.4 m (standard width) |
Examples
Bricket Wood
Two extended-height L8-series D30 towers were inserted into the Sundon–Elstree 400 kV route just outside of Bricket Wood, Hertfordshire; the route passes alongside M25 junction 21A (Bricket Wood Interchange), 51.715° N 0.371° W. Sundon–Elstree is an L2 route, and it seems likely that the L8 towers were introduced as replacements in order to increase clearance when constructing the M25 motorway. The comparatively sunny picture is from 13th March 2021, and the dismal photos are from 30th July 2022.
National Grid’s GIS data still lists the two L8 towers as L2 from 1956, as this is an L2 line.
Documentation
- L8(c) Towers & Foundations (35/8744, drawn 1977, last revised 1983), covering D, D30, D60, D90, DT, DJT, ST, SF60 and D15 and D40 EWCO
See also
- L8 pylons album (Flickr)
- L8 D30, D60 and 2 × SF60 20–60°, and L66 D30 and D2, Harker to Stella (Flickr)
- L8 pylons album (Flickr)
- Symmetrical L8 D60 (tower ZF426) (Flickr)
- L8 DJT, Capenhurst Substation (Flickr)
- L8 DJT, Inverarnan Substation (Flickr)
- L8 DJT and DT, West Ham (Flickr)
- Asymmetric L8 DJT, Thurrock (Flickr)
- Another asymmetric L8 DJT, Thurrock Substation (Flickr)