NWE SL4

Contents

• Overview
  • General data
  • Design changes
• Can be confused with
• Tower forms
  • Examples
• Tower details

Overview

NWE SL4 is distribution tower series designed by Blaw Knox. Whether any other lines use this same tower type is not known.

The NWE SL4 towers are contemporary with and to the same general design as those of SEE SL6, but the vertical conductor spacing was increased from (one presumes) 8′–6″ to 10′–6″. Of this higher clearance, [Nicholls] (1945) wrote:

In designs Nos. 2 and 4 this separation is 10·5 ft, and this was adopted specially for construction in exposed country.

Note that there remains no positive identification of the various types listed in [Marshall] and [Nicholls].

General data

Design changes

The original line tower had 8′–6″ crossarm spacing and a pyramid peak; this design was cancelled in favour of a wedge-peak design with 10′–6″ crossarm spacing. A D3°L type with reduced crossarm spacing of 9′–0″ was also cancelled.

The D10 tower was originally designed as a suspension tower. It was redesigned as a tension tower, with the original design cancelled. The cancelled version had 8′–6″ crossarm spacing; the final design has 10′–6″ spacing. The original D30 likewise had 8′–6″ crossarm spacing; the final design has 10′–6″ spacing.

The line tower peak was changed according to the then-new practice of supporting ±85° earthwire swing, and the increased vertical spacing was likely to reduce conductor flashover and clashing in high winds in exposed terrain.

Can be confused with

• Baby PL16 (66 kV?)
• ca. 1945 standard 66 kV
• SEE SL6
• Blaw Knox K9906

Tower forms

The following diagrams are shown to scale at 12 pixels per metre:

A pair of GPO crossing towers can be found either side of Barras Brow road, Dalston, south of Carlisle. No drawings have yet been recovered for these or the terminal towers.

Examples

Out of range.

Tower details

See dimensions on the site guide page for a key to the tables.