Pylon contracts

Contents

• Overview
• Contract numbers
  • Anomalies
• Primary Lines
  • Mysteries
• Secondary Lines

Overview

This page is not a catalogue of all lines and contracts, just those contracts that have a name. Not sure what this page is for but it had to be split out from the series page as part of disentangling the confusion between contract designations and tower suite designations. The entries are only in the vaguest hint of a meaningful order, as virtually nothing is known about any of these contracts, and in most cases the applicable dates are not known.

The entries below can be entire regional grid contracts, whole new lines and presumably also diversions and truncations of lines. Many of the contracts are found only as annotations on one or two drawings of existing tower types, with no direct indication of what the towers were used for.

For tower design contracts, see the drawing number ranges page.

See the regions page for a guide to the regions and their abbreviations and prefixes.

Contract numbers

Contracts originally took the name of the region followed by a type code and a sequence number. Tom Gloag has identified the following type codes:

PL

Overhead Lines

PT

Transformers

PS

Switchgear

PF

Foundations and Groundworks

CR

Control Room

Tower line contracts were given either a “PL” or an “SL” number, where “PL” is believed to denote “primary line” (132 kV) and “SL” is believed to denote “secondary line” (33 and 66 kV). That would suggest that there should also be “ST” (for secondary transformers), “SS” (for secondary switchgear) and “SF” (for foundations and groundworks) but at present this remains speculative.

By way of an example, the well-known SWE PL16 contract is the 16th primary line (132 kV) contract within the South West England and South Wales region, noted for a new tower type that became a national standard across the UK. These contracts began with the construction of the original national grid in the late 1920s and early 1930s, with a separate PL1 contract for each region.

The PL and SL numbers are only unique within a region: MEE PL1 is completely separate from (for example) CE PL1, and those two contracts didn’t even use the same type of towers. The “SWE” in “SWE PL16” is frequently dropped in the name of the tower type, but the contract (the line from Andover to Bournemouth via Salisbury) was specific to the SWE region.

Following nationalisation, a new numbering system appears to have been chosen, derived from the form “T(x) Ly”, where x denotes the applicable area electricity board and y is the contract number relative to that region. Normally an organisation abbreviation such as K&D (Kennedy and Donkin) or CEGB appears in the middle of the contract number. The L numbers again are unique only to the region. The L66/89 type took its name from the T(12) BEA – L66, Clyde’s Mill–Carlisle–Stella. The same is almost certainly true of L34 although this remains to be verified.

Anomalies

There are a few anomalies. Two contracts so far use “WM(EL)” instead of the predicted (but unconfirmed) T(7) for the Midlands Electricity Board. “WM” appears to denote “West Midlands” but the meaning of the “EL” remains a mystery.

The J L Eve S123 drawings—additional terminal tower configurations for J L Eve C534—are annotated “S.E.E. - L16”, which does not make sense. There is no other evidence for a L-numbered contracts within the CEB regions. This is potentially how C534 got its alternative designation of “L16” but this too remains unconfirmed.

Primary Lines

Original CEB PL contracts, plus later contracts for 132 kV and above.

† The CEA only existed between 1955 and 1957, and since L236 is already dated to after 1957, L256 is presumably going to be around the same time.

References:

1. Annotations to Watsham’s SEE PL7 drawings
2. Blaw Knox K4611 drawing XM1631-50A, GA&ED of type DC tower outriggers for 132 kV operation
3. Annotation to Blaw Knox K1201 drawing XM2051-28, GA of S10° tower
4. Eve drawings, thus far DT sealing end platform only
5. Annotations to SEE PL1(b) drawings
6. Annotation to J L Eve C534 drawing C534/121F
7. 47/3057 and HW tower schedule

Mysteries

The first section of route HW, T(3) CEGB – L293 (Poole–Wareham), from the junction with HH and HJ up to the first substation, uses a random assortment of towers, suggested to be the result of using up “strategic spare” towers from other lines, that were left unused, taking up space, and slowly rusting away. The tower schedule notes the following types in addition to the primary type (“Blaw Knox PL16”) used on this line:

• “Pirelli General PL1”
• “Blaw Knox PL5 W.G.R.”
• “Watshams PL7”
• “Blaw Knox PL20”
• “BK PL35”
• “Blaw Knox PL6”

None of the regions are given for these. It’s unclear how much of this route could be observed on foot. What few towers are near roads do not all match up with what the tower schedule claims they are, so it’s uncertain exactly what was erected where. HW18 is listed as “Blaw Knox PL35 DD2 Modified Peak” but in reality it is a PL4/WGR D2. HW19 “Pirelli General PL1” is an SWE PL16 (K8323) D2 with custom bracing for the top crossarm. HW16 is the same designation as HW18 (PL35) and the same tower type as HW19. “Pirelli General PL1” however is verified by an annotation on the SEE PL1 D30 E10 and E20 stress diagrams drawing, no. 6259. (Note that the “a” in SEE PL1a was not originally present on the drawings and was added afterwards to some but not all.)

Secondary Lines

33 kV and 66 kV on lattice towers, mistakenly referred to as “pre-Grid” towers. The expansion of “SL” as “secondary line” is unconfirmed, but PL contracts were all 132 kV and all SL contracts were for towers designed to support 33 and 66 kV (with the voltage often not noted, and ambiguous given the way that SL towers were designed, with crossarm spacing set both by voltage and by environmental conditions).