PL4 and WGR

Contents

• Overview
  • General data
  • WGR
  • Single circuit
• Can be confused with
• Lines
• Tower forms
  • Single circuit
  • Double circuit
• Tower details
• See also

Overview

PL4 is a UK electricity pylon (steel lattice transmission tower) series. PL4 is one of only a few series to support double earthwires, doing so with separate earthwire crossarms. PL4 appears to be a revision of CE PL3 that added extra clearance to the earthwire (or earthwires in the case of double earthwire towers).

The towers were designed for scheme CE (Central England) PL4. The name has been simplified to “PL4” as it has been used for later schemes across the UK. The series is also known as “WGR” (Wartime Grid Reinforcement) as it was used for various new lines constructed during World War II.

General data

Contractor	Blaw Knox
Found
Height (straight line tower)	86′–0″ (26.2 m) 91′–3″ (27.8 m) (double earth)
Voltage	132 kV
Dates back to	1936–37 (drawings)
Design conductor	0.175□″ SCA (now 175 mm² Lynx ACSR)
Known heights	STD E5 (+5′) (only listed for D2) E10 (+10′) E20 (+20′) E30 (+30′) (not listed for D30) E20+10′ (+30′) (only listed for D10)
Circuit count	Single, double

E20+10′ denotes an E20 extension plus another 10′ extension for a total of 30′ extra height, rather than a separate design as with the normal E30.

WGR

PL4 towers were used extensively during World War II. The majority of Wartime Grid Reinforcement (or War Time Grid) schemes used PL4 towers; consequently, the PL4 tower suite is also known as WGR, as can be seen in [Standard Tower Types]. Contract WGR PL1 is the V route from Harker to Galashiels; this is the only WGR scheme identified by name at present. At least one WGR line used PL7 towers, although PL7 has so far not been identified with the WGR name.

At least two wartime-era drawing registers exist at National Grid. The drawing schedule for WGR lists numerous drawing ranges; without examining a sample of each range it’s not possible to determine what each range represents. Additional material was listed simply under “PL4”. It appears that CE PL4 did not contain single circuit, but single-circuit towers were added to the type during the war.

† K/XM correspondence presumed but not proven

‡ With only one known drawing, one would think that this is a typing mistake for XM1425 but the large leap in BK35 numbering makes it impossible to be sure.

Single circuit

Single circuit was introduced in 1940 as Blaw Knox K5297. The scheme for which single circuit was designed has not been identified. An S60 tower can be found at Cargenbridge, near Dumfries; this is listed on the tower schedule as type “NWE”, suggesting that these towers were originally created for an NWE contract. K5297 contains both single and double earthwire although the double earthwire type is yet to have been observed.

Towers 35 through 41 on the E route from Bridgwater to Taunton were listed by Western Power Distribution as “S.W.E. PL.9 type towers”; this section of the line was diverted during World War II using K5297 towers rather than the original SWE PL1(a)&(b) type. It’s not known whether this diversion actually was SWE PL9, or simply used the same towers as SWE PL9.

Although single circuit was not part of CE PL4, it was collected under WGR by National Grid.

Can be confused with

• CE PL3
• PL16
• Blaw Knox K1201 (single circuit)

Lines

Various lines have been found to date. A few are confirmed and detailed below:

Double-circuit lines confirmed so far:

• Harker to Galashiels, WGR PL1 (V route)
• Leicester to Corby, split into two sections:
  • Leicester substation to Kibworth substation (route AZT); both ends terminate on PL16 towers. The penultimate tower at Leicester is a Milliken SS-PL1 D60, and there is a stray Milliken-like DT at the substation.
  • Kibworth substation to Corby substation (route AZ); between Hazelwood 33 kV substation and the Midland Main Line railway, the line has been undergrounded. All four ends terminate on PL16 towers.
• Corby to Eaton Socon substation, St Neots (route PFZ); this is said to be Corby to Little Barford, although Eaton Socon substation to Little Barford substation is now the short L7(c) route PGH. Around Grafham Water there are Eve 0.4 towers; the exact extent of these towers cannot be determined due to the line’s distance from roads.

Tower forms

The K5784 War Time Grid Reinforcement drawing schedule includes both single and double circuit towers. Single-circuit WGR lines have yet to be identified however.

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

Single circuit

S60 DEW is taken from the erection diagram. S2 is cloned from CE PL3 as the towers along the Taunton diversion appear identical. The S60 body dimensions appear to be identical to that of K1201.

The ST tower is found at Middleton in Lancashire, and is believed to be the only tower left from the former Quernmore–Heysham line; as this line was PL4/WGR single circuit, this tower is presumably PL4/WGR also. The same tower type was used at Thorton-Cleveleys for each of the two circuits on the former Blaw Knox K5735 line from Preston.

Double circuit

Details on the terminal towers are unclear. CEA drawing ED51147 names the type as “D.D.T.90°.TOWER” but specifically shows the tower without auxiliary crossarms (omitted from the side view). Variants “A” and “B” are depicted as per drawing ED51147, without auxiliary crossarms. However, there most certainly are PL4 DDT90 towers with auxiliary crossarms. Variant 1 above is depicted with a preliminary depiction of the auxiliary crossarms as seen on a WGR tower at Upper Boat Substation, South Wales (between Pontypridd and Treforest Industrial Estate, 51.576° N 3.297° W). The next tower is a DD60 (51.576° N 3.294° W), after which the line changes to PL16. DDT90 variant 2 depicts the WGR tower found in Watford, Hertfordshire, England (see links below) with a longer middle auxiliary crossarm. There is also a terminal tower at Blackburn Substation (see links below) without auxiliary crossarms that would better fit the description of DDT.

ED51147 was drawn on 18/12/1956 and originally covered only a single design. Variant “B” was added on a date that one would presume says “7·5·58” (because “7·5·56” would make no sense as an amendment); this second variant represents a tower used in or at “Sundon”, presumably Sundon Substation, a tower that appears to no longer exist. Variant B is simply Variant A without the extended length top crossarms; the remainder of the tower is identical.

The D2 towers in Barrow-in-Furness (NWE PL10) have replacement earthwire peaks and top rakers. The double earthwire towers (line and angle) have—with the exception of the crossing over the Lower Ormsgill Reservoir (DD10 and DDT)—been converted to single earthwire, but even existing D2 towers have been modified to match:

Tower details

Crossarm width is the total width across the widest crossarm.

See also

• V route (WGR PL1), Harker to Galashiels (Flickr)
• Assorted WGR towers (Flickr)
• WGR DDT90 and PL1a DT90, Watford 132 kV substation (Flickr)
• PL4 or WGR DDT, and PL16 DT at Blackburn Substation
• WGR PL1 DD30, Carlisle (Flickr)
• WGR PL1 DD90, Carlisle (Flickr)