- Compliant tower suites
- L132 as a designation
- Tower types
CEB L132 is a specification for a 132 kV towers, dated 1940. The specification is very broad in scope and sometimes a little limited in terms of specifics, although at least some of the missing details will be in the schedules. The conductor and earthwire copper equivalent cross section areas appear not to be mentioned at all but these may have been detailed in Schedule D.
Including the title page, the Central Electricity Board Specification for 132 Kilovolt Overhead Transmission Lines is 33 pages long. However, many details are included in the various appendices, entitled “Schedules” of which there are at least nine. Presently, only the specification itself has been obtained.
Compliant tower suites
Three tower suites are known to comply with L132:
- Blaw Knox 0.175□″ conductor generally known as “PL16”
- J L Eve 0.175□″ conductor
- J L Eve 0.4□″ conductor, sometimes known as “L16”
J L Eve 0.175□″ conductor is verified to be L132-compliant from at least two sources including J L Eve drawing C670-196 (JE35/33751) from 19th November 1973.
SWE scheme PL16 was Blaw Knox contract K8323. [Telecoms Work on Overhead Lines] gives the specification “L132 (PL16)” for both K1124 and K8323, and National Grid’s K1124 drawing schedule also gives the specification as “CEB L132 (PL16)”.
Confirmation for J L Eve 0.4□″ conductor is not as concrete yet nonetheless sufficient. [Wires Pipes Pylons] illustrated two CEB L132 types:
The 0.175□″ conductor tower shown is identical to PL16 D2S. The 0.4□″ conductor type is effectively identical to “L16” D2. [Brechfa Forest Connection] contains one of the few rare references to CEB L132:
The preferred solution is to add a further extension to tower C17. This is a type D10 E10’ tower constructed to specification CEB L132 (0.4 sq in conductors) …
Tower C17 does indeed match the “L16” design.
L132 as a designation
“L132” is also used as a tower description. Thus far, all discovered instances of towers described simply as “L132” have been found to be the Eve design. Although L132 can be used to refer to PL16, “L132” and “PL16” can be found together in the same document. For example, [SWS Forum 08/06/2017] shows both PL16 and L132 lines (also “L1” but that appears to be erroneous and intended to read “PL1” based on the towers found on those lines). [Overhead Line Conductors Carrying Optical Fibres] also names L132 and PL16 separately:
OPPCs and OPGWs are intended to be direct replacements for the conventional equivalent conductors used on wood pole lines or steel tower overhead lines of PL1, PL4, PL9, PL10, PL16, L2, L3, L4, L7, L9 or L132 construction operating at 33kV or 132 kV.
Such references to “L132” as a separate tower type could conceivably be either of the two Eve types.
On his LinkedIn page, LSTC engineer Zainul Hassan briefly describes a refurbishment project on a line that “consists of 21 x PL16 towers and 6 x L132 towers”. Zainul has never responded to queries regarding the nature of the L132 towers or the line involved. The work included “Replacement of existing Lynx conductor with AAAC Poplar” which is the expected conductor type for PL16. Had even just the line been identified, then it would have been possible to examine at least a portion of the line in Google Street View and verify the appearance of the towers in question.
Both of the Blaw Knox and J L Eve 0.175□″ types also appear to be compliant with the Scottish specification STL1.
Single circuit tower types are named as S2°, SS2°, S10°, SS10°, S30°, SS30°, S60°, SS60°, SX (transposion) and SST and SST90° (terminal). “SS” denotes single circuit double earthwire.
Double circuit tower types are named as D2°, DD2°, D10°, DD10°, D30°, DD30°, D60°, DD60°, DX (transposion) and DDT and DDT90° (terminal). “DD” denotes double circuit double earthwire.
Note that single earthwire terminal towers are not included. Such towers do nonetheless exist.
S10°, SS10°, D10°, DD10°, SX and DX towers are all designated for use as section towers.
Earthwire changeover—towers where the line changes from double earthwire to single earthwire—was assigned to SS10°, SS30°, SS60°, DD10°, DD30° and DD60°. For double circuit this is confirmed by the drawing suite used by the Tower Bible although these drawings are missing from the original Tower Bible itself. DD90° EWCO is not supposed to exist but such a tower has been found at Meaford.
The SX and DX transposition towers use the same design as S10° and D10° with appropriate modifications to the crossarms.
The entry angle for all terminal towers is given as 45°, confirming what is widely seen in the field.
No tower suite is known to contain the entire set of designated types. Blaw Knox designed both single and double circuit towers but transposition towers are not known from any tower suite after SEE PL1a. J L Eve are not presently known to have designed any single circuit towers.
Owing to copyright, the specification is not provided in full. Instead, the table of contents is listed along with brief notes on the 60 clauses contained within the document. The notes below do not spell out every stipulation made by the specification but rather just a few interesting points of note.
The schedules were not included with the copy of the specification. The purpose of each schedule has been derived from the specification. Some of the schedules appear to be definitive—written at the same time as the specification—and others appear to be descriptive, populated over time as required based on for example tender submissions.
|A||Sites and routes|
|C||Manufacturers and places of manufacture, testing and inspection|
|D||General particulars and guarantees: conductors, insulators, fittings, tower dimensions etc.|
|E||List of drawings, samples and models and provisions of such|
|H||Indicated in separate places to be the prices and standard height extensions; the former may be a mistake where Schedule J was intended|
|J||Unclear; additional material and price stipulations?|
|1||Nature of Work||The specification covers 132 kV overhead lines to be part of the “Grid system”.|
|2||General Particulars of System||Brief overview of the electricity grid. The working voltage is noted to not normally exceed 10% of the nominal voltage.|
|3||Extent of Work||The specification is not simply for the design of the towers but for a specified set of complete overhead lines along routes detailed in Schedule A to prices stated in Schedule H.|
|4||Dates for Completion||Given in Schedule B.|
|5||Places of Manufacture||Detailed in Schedule C.|
|6||Design||Brief stipulations regarding inspection, cleaning, repairs and resiliance to vibration and the environment.|
|7||Compliance with Regulations|
|8||Interchangeability||This refers to the individual parts, i.e. manufacture within tolerance.|
|9||Quality of Material|
|10||General Particulars and Guarantees||Stated in Schedule D.|
|11||British Standard Specifications|
|12||Drawings and Samples|
|14||Supervision and Checking of Work|
|16||Responsibility of Contractor|
|17||General||Line conductor characteristics are included in Schedule D; this schedule is likely to be where 0.175□″ and 0.4□″ copper-equivalent cross section areas were noted. Within clause 17, two conductor types are named: steel-cored aluminium compliant with BSS No. 215 (later BS 215) and cadmium copper compliant with BSS No. 672. Aluminium is to be of the highest commercially-obtainable purity with certified details as to impurities. The steel core wires are to be galvanised. Nothing is said regarding aluminium versus cadmium copper conductors, but cadmium copper lines were a wartime emergency measure used on the Wartime Grid Reinforcement lines built using the same towers as CE PL4; reference to cadmium copper conductors was deleted per amendment sheet 2.|
|19||Connectors||Aluminium to copper connectors must be of approved types and be designed to prevent electrolytic action between dissimilar metals.|
|21||General||Lines are to have a single earthwire except for the first mile outwards from each substation where the line is to have twin earthwires. No reason for twin earthwires is given. The earthwire characteristics are given in Schedule D.|
|22||Joints, Clamps and Dampers|
Insulators and Fittings
|23||General||Both suspension and tension insulators are to be cap and pin type with ball and socket fittings. Suspension insulator sets are to be anti-fog of minimum length 55″ while tension insulator sets are to be standard type of minimum length 56″. “Low-duty tension” sets—for example those used with downleads—are also to be the anti-fog type. This distinction can be readily seen on 132 kV lines.|
|24||Material||The insulators are to be made from ivory white porcelain with a brown glaze.|
|25||Guard Rings, Arcing Horns and Arcing Distances||The arcing distances (between arcing horns and guard rings) are 39″ for the first mile from the substation, 44″ thereafter, and 48″ at railway crossings. This general practice remains in effect while double earthwires went out of favour with subsequent tower designs.|
|27||Mechanical Design||One of the stipulations is that porcelain and hard metal must not touch; a “suitable yielding” material such as cement should be placed in between.|
Steel Towers and Foundations
|30||General Design||Clause 30 refers to drawing C.E.B. 1·977 for approximate general proportions. This drawing shows towers that look to be based on Milliken, SEE PL1, SEE PL1(b) and CE PL4. The bend line is stipulated to be at the height of the middle crossarm. The tower must then taper by 4 or 8 inches—for single and double circuit respectively—to the top crossarm.|
|31||Types and Use of Towers||Tower types as noted above. Height extensions as detailed in Schedule H.|
|32||Single and Double Circuit Transposition Towers||Details noted above.|
|33||Span Lengths||The normal span was given as 900 feet, with two successive spans permitted to sum to 2000 feet so long as neither span exceeds 1500 feet. With line towers, the sum is reduced proportionally down to 1600 feet according to the level of deviation between 0° and 2°. The paper copy of the specification was later amended by hand with higher limits. The normal span was increased to 1000 feet, as demonstrated in [Wires Pipes Pylons]. The sum of adjacent spans was increased to 2200 feet, reduced to 1700 feet for line towers at maximum 2° deviation. At the engineer’s discretion, higher angle towers can be used in straight line positions or with relatively small angles of deviation; this allows for a sum of adjacent spans to exceed 2000 (later 2200) feet, so long as no single span exceeds 1500 feet..|
|34||Conductor Spacing and Clearances||Ground clearance is 22′. Clearance to fences, walls, buildings or any structures on which a person may stand is 12′. Phase clearance (separation) is 12′. Clearance to vegetation and other wires is 8′; clearance to vegetation and where any tree may fall was later amended to 12′.|
|35||Foundations||Foundations can be concrete or rock. Significant details are given with regards the composition and manufacture of the concrete.|
|36||Assumed Working Loadings|
|37||Assumed Broken Conductor Conditions|
|38||Factors of Safety and Testing of Towers|
|39||Construction||Amongst other things, this clause appears to indicate that towers can be assembled horizontally on the ground and then lifted into a vertical position; the tower must therefore be able to withstand such loads without harm. “Approved means” are required to avoid livestock getting caught; no further details are specified as to how, but generally cattle guards were a metal strip just above ground level between each leg and the diagonal bar on each side of it.|
|41||Workmanship||One condition is that not less than 1% of steel members of each type is to be selected at random and built into complete towers at the manufacturer to verify suitability. This will also relate to clause 8 with regards the interchangeability of parts.|
|43||Anti-climbing Devices and Steps||Anti-climbing devices are to have hinged sections on each corner with step bolts in order to allow for maintenance access. Bronze locks are to be used to keep the tower secure in normal operation. Step bolt spacing must not exceed 15 inches; no minimum spacing is provided.|
|44||Danger, Property, Route and Number Plates|
|45||Phase and Circuit Plates||Each tower is to have phase colour plates indicating the phases (red, yellow and blue); this no longer appears to be in force. Double circuit towers must also indicate which circuit is which.|
|46||Earthing of Towers|
|47||Botls and Nuts|
Setting Out and Erection
|49||General||Wayleaves and other related concerns are the responsibility of the CEB, not the contractor. Initial route planning, including approximate siting of terminal and angle towers, appears to also be the CEB’s responsibility; the contractor is require however to finalise the exact location of every tower. The contractor is responsible for alterations to the route to keep the conductors within weight tolerances. This section details cost responsibilities and procedures for site access and both temporary and permanent changes to sites during construction.|
|50||Access to Site|
|51||Foundations||“Templates” are to be used to determine and maintain the correct positions of the stubs. The foundations must then be left fourteen days to set before erecting a tower onto them (notwithstanding cement type and location conditions).|
|52||Erection of Towers|
|54||Erection of Conductors||This clause includes a note regarding the number of vibration dampers to be used. For spans exceeding 1000 feet, there are to be two dampers at each end of the conductor instead of one.|
|55||Transposition||Deleted per amendment sheet 2.|
|56||Sags and Tensions|
|57||Supervisory Staff and Erection Gangs|
|58||Plans and Profiles|
|59||Measurements of Work and Payment|
|60||Payment for Tower and Foundation Work|