Pylon questions
Currently outstanding questions about UK electricity pylons and about this site.
Contents
Site questions
- What is the best way to depict partial approximations? That is, diagrams where part of the drawing is based on industry material and parts of it are based on Street View. The dotted outline form is too easy to mistake for optional components but using a colour implies a highlight and thus a greater level of certainty.
- What is the best way to handle depiction of crossarm plans? That is, both the bracing along the bottom of the crossarm, and the planform of the crossarm. Both are helpful for recognition. In planform, crossarms can be rectangular (“square-ended”) as well as triangular and even dovetail. Triangular-plan crossarms on terminal towers can be isosceles or right-angled, and right triangle crossarms can be forwards-facing or rearwards-facing (or both on the same tower). Sometimes it’s necessary to double check crossarm plans for recognition purposes, and at present these details are not yet revealed as it has yet to become clear how to do so.
- Should each L6 type be split onto a separate page to ease page complexity and allow for subtype-specific overview images? How about the two L3 types?
- Is the main series page becoming overloaded with images? Should it be constrained to, say, just line towers and 30° towers?
- Should the 10° and 30° pages be merged? The 30° page already covers 20° towers, and the difference is sometimes sufficiently subtle as to make it difficult to guess which page to check. Various tower series use the same tower (above ground) for 10° and 30° deviation limits.
- Should some means be applied to indicate tower types believed to be extinct (e.g. K5735)? One option would to be draw such towers in red, although red is an unfortunate choice at the moment as it conflicts with the BB L6 diagrams where red indicates corrections made to incomplete source material.
Pylon questions
Terminology
- What to the contract (E, L, K, T) and drawing (LT, XM) numbers mean in Blaw Knox drawing numbers, and how were they allocated?
- Some of the tower type designations (e.g. DTU, STX) remain undefined: what do they each mean? Moreover, what is the meaning of DTV 45° (0–5° entry)? What does the 45° indicate if not entry angle? Also, why did National Grid change this to DTU45?
- Is it true that “crossarm” originally referred to a pair of arms on the basis that they were a single assembly? (In more recent decades, the arms on each side are completely separate to allow individual replacement and correspondingly appear to be treated as pairs of crossarms.) — unclear, but in the 1930s, crossarms were redesigned with separate left/right units, so that either side could be repaired individually.
- Is there any definitive, conclusive information on the “(c)” and “(m)” suffixes, especially with regards to L4(m) versus L6(m)? There seems to be contradiction as to which one denotes nearest metric sizes and which one indicates a redesign, and the exact manner of the redesign.
- What is the definition of a panel? This is a portion of a tower but it’s not clear what it means. For L3(c) it denotes a large section of a tower while for Milliken E177 it just seems to denote the points where bracing attaches to the tower corners. One view is that it relates to height extensions.
Structural
- What is the advantage of using duplex (paired) insulator strings? They are common in countries such as Germany, but not typically used in Britain, with notable exceptions: GPO crossings (for redundancy) and L6 (to share the same insulator sets between twin and quad Zebra towers, with duplex sets for quad Zebra).
Electrical
Why does Britain use shorter earthwire peaks (and thus lower earthwire shade) than say Germany?— It does not: the placement of two side-by-side phases on the lower crossarm on many German towers requires a taller peak to maintain sufficient earthwire shade which, on average, is the broadly the same range of shade angles as the UK.- What are the criteria for requiring an earthwire? For example, most 132 kV steel tower lines have one, but a few lines in Scotland do not. “Trident” wood pole 132 kV lines do not either, just as how 11 and 33 kV wood pole lines do not.
By series
PB
- Where does the “PB” designation come from, and was this type solely a Painter Brothers product from design to fabrication? — The official designation is “Painter’s Universal or PU Pole”, also written as “PU pole”, and it is Painter Brothers’ own design. The “PB” name however remains a mystery, in terms of who actually uses it and why.
L2
- All known gantries seem to be SFX. What does “X” stand for? The existence of DJ/DJX and ST/STX suggests that there should also be an SF, but so far there is no evidence of one.
L3
- What gantries does L3 have? (Both Eve and Blaw Knox)
L4
- Was there ever an imperial L4 pre-dating the metric L4(m)? That is to say, does the “m” indicate that L4 was metric from the start, or does it denote a metric adaptation akin to L6(m)? — See the L4 page for notes on this.
PL16
- Was single circuit ever part of the English suite?
Other
Velograph copying
There existed a system for copying drawings known as a “velograph”. These are referenced in the SWE PL16 specification (schedule E paragraph 2):
Drawings for approval shall be submitted in duplicate as blue prints and, after having been approved, the Contractor shall supply any further copies required by the Engineers, one copy at least being a velograph print on tracing cloth.
There is another reference in CEB L132 under clause 58:
After completion, velograph copies of finally approved profile drawings specified in Clause 49 shall be supplied. These drawings shall correctly show the ground contours, tower types and positions, and clearances between conductors and ground at 50°C (122°F).
J L Eve used velograph copies of their C673 drawings for C864, as noted on the drawings themselves (e.g. “ORIGIN VELO OF C.673/169” on C.684/48).
So far, no trace has been found of what exactly a velograph print or copy is.