Pylon questions

Currently outstanding questions about UK electricity pylons and about this site.

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? These are helpful for recognition.
What is the best way to show square-ended crossarms? This too is helpful for recognition.
Should each L6 type be split onto a separate page to ease page complexity? 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?

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 there any vague consensus as to the definition of “crossarm”? Is there one crossarm per cable or one per level/tier? Depending on where you look, it seems that it can be either, so what do the “one-per-level” folk call the arms on single-circuit towers (that are only on one side of the tower)? The term “arm” however does also get used in various places.
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.

What is the advantage of using paired insulator strings? They are common in countries such as Germany, but seldom seen in Britain (mostly commonly on the line towers of some L6 sections, such as in the Wymondley area) and are being phased out in Britain as lines are reconductored. Likewise, quad-conductor lines are being reduced from quad insulator (one insulator per conductor within the bundle) to twin insulator (two conductors per insulator).

~~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 do not.

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.

All known gantries seem to be SFX. What does “X” stand for, and was there also a standard SF tower? Does the X relate to that in DJ/DJX and ST/STX?

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)?