L12
Contents
Overview
L12 is a UK electricity pylon (steel lattice transmission tower) series. L12 comes in both standard height and low-height varieties. The low-height type is similar to L9, but clearly differs in its use of simple suspension insulators, as shown in the diagram below.
In a 2008 members-only post by Jules Seifert at the Pylon Appreciation Society forum, he claims that “L12 was designed specifically to take twin Redwood (AAAC) conductor rather than the quad Zebra (ACSR) and there are three versions of L12 towers in the field.” No further elaboration was offered. In reality, L12 was designed for twin Araucaria (700 mm² AAAC). Details on the three versions are unclear, but the one known change is the terminal towers, which were redesigned.
The low-height suspension tower is designated “L12 LD”, as shown in [Transmission tower development].
L12 is a twin-conductor type, but there is an L12 D25 in Imperial Park, Duffryn, Newport, Wales being used as a conversion point between L6 quad conductor to L12 twin conductor, at 51.552° W 3.047° W, on the Imperial Park–Cilfynydd 400 kV line. A second conversion tower from twin back to quad can be found at 51.554° N 3.016° W on an unnamed line on the opposite side of Imperial Park Substation; this tower may be L6.
As of February 2023, National Grid’s approach to new heavy-duty lines is said to be D and D30 from L6 and all other tower types from L12, with steelwork upgrades to L12 as required.
L12X
SSE400 is a heavy duty derivative of L12 designed for the Beauly–Denny line that crosses the Scottish highlands. Near Denny however, L12X is used; according to a members-only post on the Pylon Appreciation Society forum from “zulumike”, “Where the line comes down from the Highlands towards the SPT area the towers will change to an L12X specification which a strengthened standard L12 design.”
General data
Per Technical Specification 43-11 (Issue 1, 1984) 400kV Steel Tower Transmission Lines – Specification L12 (excluding tower dimensions):
| Height (straight line tower) |
46.5 m (standard height) 35.3 m (low height) |
|---|---|
| Voltage | 400 kV |
| Dates back to | 1984 (specification) |
| Conductors | Twin |
| Design conductor | 700 mm² AAAC (Araucaria) |
| Design earthwire | 425 mm² AAAC (Totara) |
| Normal span | 360 m (equiv. 1181′) |
Tower forms
The following diagrams are shown to scale at 12 pixels per metre. L12 standard height:
The Indicative Pylon Schedule document from National Grid, from the North Wales Connection Project, indicates proposals for L12 D30, L12 D33 and L12L D30. Tower details for L12L are not known, but D30 and D33 are not given as standard types. L12 D30 is definitely used, however, according to National Grid data.
The exact form of the D35EC is not known; one such tower is said to have been constructed at Woolavington, but no clear depiction is available. The depiction is taken from an inaccurate National Grid drawing for D55 and D35EC.
L12 low height:
Tower details
Crossarm width is the total width across the widest arms.
| Type | Source | Height | Base width | Crossarm width |
|---|---|---|---|---|
| L12 D | Hinkley Point C | 46.5 m | 7.1 m | 18.2 m |
| L12 D10 | Hinkley Point C | 45.3 m | 7.5 m | 17.9 |
| L12 D25 | Hinkley Point C | 45.3 m | 9.1 m | 18.6 m |
| L12 D35EC | 61/9588 | 45.6 m | 10.9 m | ? |
| L12 D55 | Hinkley Point C | 45.8 m | 10.9 m | 19.4 m |
| L12 D90 | Hinkley Point C | 49.0 m | 14.5 m | 22.9 m |
| L12 DT | Hinkley Point C | 49.0 m | 14.5 m | 29.1 m |
| L12 LD | Richborough 5.4.2D | 35.3 m | 7.06 m | 29.7 m |
| L12 LD30 | 61/9593 | 35.4 m | 7.58 m | ? |
Examples
Comparison with SSE400
Examples
There are no known L12 towers within travel distance, and thus no photographs here.
See also
- L12 DJ, near Immingham (L6 DJ according to National Grid!) (Flickr)
- L12 towers near Ulceby/North Killinghome (D and D55) (Flickr)
- L12 towers (D30 and D) (Flickr)
- L12 towers (Flickr)
- L12 towers, Teesside (Flickr)
- L12 and L2 towers, Teesside (Flickr)