Pylons site guide
Contents
Diagrams
Authenticity
All tower type diagrams shown on this site reflect towers that have been observed or documented.
Key
| Solid lines indicate elements that have been taken from official material. The line thickness is always 1 pixel regardless of the size of the steel bar. The accuracy of these lines depends entirely on the quality of the source material; even general arrangement and erection diagrams are not always accurate. | |
| Thin lines indicate elements at the rear of the tower, such as zig-zag bracing on Eve and BICC L6 peaks and crossarms that are different from front to back. | |
| Medium dashed lines indicate optional components such as crossarm extensions and outriggers. This is an official convention in industry drawings. | |
| Short dashed lines indicate bracing members that are not always present due to variations in design and amendments to towers. | |
| Dotted lines indicate approximations, typically diagrams derived from sources such as Google Street View. This is done when no diagram is available or the diagram is incomplete or inaccurate. | |
| Broken dotted lines indicate optional components within approximated diagrams. | |
| 40% opacity indicates a tower type where the design is known but no examples had been constructed at the time that the diagram was posted to the site. |
Dimensions
The diagram below illustrates the key dimensions given for towers on this site:
Specifically:
- Height
- The height of the tower from the ground to the top of the tower peak. Depending on the design, a small part of the tower peak may extend slightly higher than this dimension.
- Base width
- The width of the tower at ground level, not including the concrete muffs. In technical jargon, this is often referred to as “back-to-back [of] stubs at ground level” or “outlines at ground level”; some drawings instead give the outer dimensions of the top of the stubs.
- Crossarm width
- The distance between the widest crossarm on each side. In most cases, the distance given is between the conductor positions; the steelwork extends a little further outwards.
- Overall width
- Some pages use “overall width” instead of “crossarm width”.
- Peak to top crossarm
- The vertical distance from the top of the tower peak to the underside of the top crossarm.
- Crossarm spacing
- The vertical distance between the undersides of the crossarms, where the crossarms are evenly spaced. In many cases, the top and middle crossarms are a different distance apart from each other than the middle and bottom crossarms are from each other, and thus each distance is noted separately.
- Top crossarm to middle crossarm
- The vertical distance from the underside of the top crossarm to the underside of the middle crossarm.
- Top crossarm to bottom crossarm
- As above, but from the highest to lowest crossarm on a single circuit tower, where the middle crossarm is on the opposite side of the tower.
- Middle crossarm to bottom crossarm
- The vertical distance from the underside of the middle crossarm to the underside of the bottom crossarm.
- Bottom crossarm to ground
- The vertical distance from the underside of the bottom crossarm to the ground line.
Conventions
For the sake of consistency, certain conventions are applied to the material on these pages.
Tower diagrams
The tower diagrams on this site are based on a variety of source material. The source material takes a variety of forms from simple wire mesh diagrams (as used on this site) through to detailed erection diagrams. Since it is not possible to obtain detailed plans of every tower type, and because a significant number of source diagrams are simple wire meshes, all diagrams presented here are in simple wire mesh form. Wire mesh outlines do contain a number of simplifications; in particular, bracing members tend to be shown meeting at single points where in reality they may not do so. Gusset plates are omitted, even for tower types where they are a highly prominent feature of the design, for example L7 angle towers.
The depiction of insulators in suspension tower diagrams is being harmonised to generic types. The length of an insulator string (tension or suspension) including the size, shape and count of units within the string depends on various factors beyond simply the voltage, so the generic forms shown on this site are for clarity only. Likewise, the colours shown have no bearing on the actual materials used, which vary considerably across the country. Insulators are not shown for tension towers.
Chirality
Some towers (especially SEE PL1(a) single circuit) are flipped horizontally for consistency with respect the official drawings, to make recognition easier. In practice it appears that some lines no longer follow the correct practice of front/rear face anyway (when looking along the line towards higher-numbered towers, the front face of the tower is facing you).
Nomenclature
Industry nomenclature has changed in accordance with changes to British practice. For example, a “Mrs Smith” might now work at the “BBC”, while previously a “Mrs. Smith” would have worked at the “B.B.C.” The Tower Bible goes the other way and uses extraneous punctuation for no reason at all. For example, the Blaw Knox standard tower is given as “D.2.° TOWER.” with extraneous dots. (The dot in “2.°” is written under the degrees symbol.) Conventionally, deviation angles were written with the degrees symbol, but this has since been dropped. What was once written “D.30°” or “D.T.” is now simply “D30” or “DT”.
This site follows current practice entirely, regardless of the design age of any tower type.