SEE PL1(b)

Contents

• Overview
• Tower forms
  • Single circuit
  • Double circuit
  • Examples
• Tower details
• Examples
  • Crawley
  • Maidstone
• See also

Overview

South East England (SEE) PL1(b) is one of the original national grid schemes, covering approximately the South East England region south of the Thames (although the exact scope of SEE PL1(a) and PL1(b) is not confirmed). The towers were designed by Callender’s. This is in contrast to most PL1 schemes which used Milliken towers. The northern half of the South East England region was designated PL1a and used different towers, seemingly designed by GEC.

For years, it seems that the industry and enthusiasts alike forgot that SEE PL1(b) existed, and the term “PL1b” was mistakenly applied to the “PL1” Milliken towers that formed much of the original national grid, seen for example in [NSP/004/030]. One explanation for the difference between “PL1” and “PL1b” was given as “These were minor changes, possibly vanity jobs for incoming senior management of the CEB! Literally minor structural changes, the conductor separation and basic spans stayed the same …” In reality, SEE PL1(b) is a completely different tower suite, designed by a completely different contractor (Callender’s) from the typical Milliken PL1 towers. SEE PL1(b) must not be mistaken for the type used for SWE PL1(a)&(b), also Callender’s but a different design; see SS-PL1 for details.

SEE PL1a and PL1(b) share a common design feature of an integrated anti-climbing device. Most tower suites use adjustable anti-climbing devices; these can be positioned within a range of heights from the ground. PL1a and PL1(b) instead set the anti-climbing device at specific height from ground level: 19 foot for SEE PL1(b) D2, 25 foot for D30 and 18 foot 5 inches for PL1a D2. The heights all differ and correspond to the bracing structure, and are not where the network operators want the anti-climbing devices positioned. In practice, conventional adjustable anti-climbing devices are used instead at a lower position, leaving vestigial projections at the originally-intended height. These projections can be used as a recognition aid to narrow down a tower to PL1a or PL1(b); this helps with single circuit towers as those are less distinct from each other than double circuit towers. The diagrams on this site omit anti-climbing devices, but the integrated ones in PL1a and PL1(b) are shown as they are a part of the tower.

Tower forms

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

Single circuit

The S30 and S60 diagrams were traced from Google Street View, scaled according to the relationship between D2 and D30. This resulted in plausible base widths of almost exactly 18′ and 19′–6″ for the S30 and S60 respectively.

Double circuit

The DX transposition tower is formed from the D30 with custom crossarms. Presently the only known extant example can be found adjacent to Shottendane Road, Garlinge, near Westgate in Kent, but further examples may still exist; the example in Garlinge does not have the supporting bars under the bottom crossarm.

The DT tower seems to have the same body dimensions as the D60 but with different bracing, and the top crossarms are longer. The DT diagram was traced from a photo of the terminal tower in Maidstone, Kent. The DT90 diagram is derived from photographs and StreetView and the crossarms are only very approximate. Both the DT and DT90 have a peak that is vertical at the front, as illustrated below:

Examples

Tower details

Crossarm width is the total width across the widest crossarm pair (double circuit) or across the longest crossarm on each side (single circuit). Some crossarm measurements are given in the general arrangement drawings only to the tower face (with no measurement across the tower at that height), so these have been (mis)calculated using rusty trigonometry …

Examples

Crawley

Three Bridges in Crawley was a node on the original national grid: single circuit lines, connected by single circuit line to Brighton to the south and Tunbridge Wells to the east (specifically Colts Hill, between Pembury and Paddock Wood). The line to Pembury Grid Substation remains, but Crawley to Brighton is now L3 double circuit.

The following photographs were taken on pylon hunt 27, 12th April 2024.

There is a short line at the substation comprising PL1(b) DT90 and D60 and a PL7 DT. One of the two circuits is disconnected at each end.

The single-circuit line from Crawley to Tunbridge Wells is part of the original national grid. The line starts out on L3 towers, before splitting out onto the original Callender’s line.

Maidstone

Maidstone is the location of a now-unusual junction. The original SEE PL1(b) double circuit national grid route ran from Northfleet to Canterbury via Maidstone. The circuit on the north side of the line bypasses Maidstone completely. The other circuit splits out to Maidstone at Pendenden Heath on a triangular junction formed from what appear to be three D60 towers:

Subsequently a new SEE PL7 line was constructed from Northfleet to Hastings; the PL1(b) and PL7 lines meet at Great Buckland (east of Halling) and the two lines exchange destinations: the PL7 line joins onto the PL1(b) line to Maidstone, and the PL1(b) line continues to Hastings.

The following photographs were taken on pylon hunt 33, 14th September 2024.

Maidstone is suggested to be the last remaining triangular junction in the UK. This role would later be filled by the DJT tower type, and the other triangular junctions appear to have been demolished along with the lines the joined.

The DT at Maidstone Grid substation originally connected Maidstone’s power station, at Fairmeadow, to the national grid. As reported in the Kent Messenger Maidstone on the 16th of September 2016, the power station was demolished in 1973, having originally been constructed in 1900, around 30 years prior to its connection to the grid. Maidstone now only receives power from UK Power Networks, rather than also supply it.

See also

• SEE PL1(b) D2 and D30, Throwley Forstal, Kent (Flickr album)
• SEE PL1(b) S2 and D2, Canterbury (Flickr)
• SEE PL1(b) S2 and D2, Canterbury (Flickr)
• SEE PL1(b) S2 side view, Crawley (Flickr)
• SEE PL1(b) S2 and PL16 D60, Crawley (Flickr)
• SEE PL1(b) D10, unconfirmed (Flickr)
• SEE PL1(b) D60, Surrey (Flickr)
• SEE PL1(b) DT90, Crawley (Flickr)