Anglia Electrification Part 2: Overhead Line Neutral Sections (OHNS)

Just to have some further ado, I'll share this diagram first before beginning a chronology of this matter. To have a slightly better quality image, which may then be downloaded and finally become something legible, I have also put it on a flickr account here: https://flic.kr/p/2qx4vK1.

This diagram compares information from three main sources on the locations of overhead line neutral sections (OHNS) in Anglia region both past and present. OHNS locations are given a lable with 2 or 3 colour coded text boxes that refer to those different sources.

If anyone isn't aware, a neutral section is a short section of permenantly earthed overhead line designed to insulate against the voltages on either side (so for a 25kv system, the neutral section insulates 50kv). Neutral sections are nessasary in order to seperate different feeds on an AC system that may not be synchronised with each other. This is because the single phase electrification system has to routinely swap which of the 3 phases it takes from the electricity grid in order not to unduly unbalance the grid supply. DC systems (or AC systems using their own power supply instead of the national utility network) don't need neutral sections and can have multiple feeder stations feeding the same electrically common section. 

On British systems, neutral sections can appear at feeder stations (FS) where that station takes two seperate grid feeds and distributes them in either direction from that feeder station. They also typically appear at track sectioning cabins (TSC) at the mid point between two feeder stations to seperate their incoming feeds (called MPTSC), also at TSCs placed on junctions where multiple different feeds meet and are distributed among adjoining lines. Sometimes an OHNS appears independantly of any track sectioning equipment and simply serves to seperate different electrification schemes that were built at different times. In the context of Anglia region, OHNSs also existed to seperate different OLE voltages either standalone but most often at TSCs and either side of feeder stations. It should be noted that some feeder stations do not use a neutral section if they only use one grid connection and are isolated at either end of their feeding section by MPTSCs or the end of electrification. These, I believe, are called "Tee feeders".

The first source here is a recent sectional appendix (September 2024) to suggest the present day situation. Next is all the information on railcodes.org which often gives indication of installation date, though without any citation. And finally below that is a compilation of the sources from 1960-1975. 

These are:

• British Railways—Eastern Region (Great Eastern Line),  Working Instructions for Electrified Lines, (internal: 1960).
  

• British Railways—Eastern Region (London, Tilbury and Southend Line),  Working Instructions for Electrified Lines, BR 31248 (internal: 1961).

• Ministry of Transport (Railway Accidents), Final report on the Accidents and Failures which occured in Multiple Unit Electric Trains in the Scottish Region and Eastern Region of British Railways, (London: HM Stationery Office, 1962). (In particular, "map 2")
  

• British Railways, Working Instructions for A.C. Electrified Lines, BR29987, (internal: 1975). (In particular, appendix B)
  

By and large all these from 1960 to 1975 agree with other on neutral section locations however there are a few descrpencies that are detailed with extra textboxes on the diagram. On the Chenford scheme, Bethnal Green (WAML) and Bishop's Stortford neutral sections were removed before 1975. On the LTS lines, it seems an OHNS was added at Chalkwell after the orginal opening of the electrification in 1960. It's listed however in 1962 and is said (by railcodes.org) to have been commissioned on 27/04/1963.

Naturally, lines which were not electified by 1962 are only recorded in the 1975 source. In particular, this is the Lea Valley main line route via Tottenham Hale which was commissioned in 1969 (pertaining to Trinity Lane and Clapton (mainline) OHNSs). Also Chelmsford to Colchester was electrified as an extention the 1960 scheme and opened in 1962 and so doesn't feature in the 1960 Working Instructions. This is relevant to Witham and Colchester (Clacton) neutral sections.

As will be discussed later, there is a slight complexity with Colchester (Clacton branch) neutral section (apparently also known as "Hunwick") in that it was originally constructed in 1959 in preperation for the extension towards London but was then resited from the twin track junction onto a single line branch and onto a diveunder on the otherside of the mainline. All this was to do with the remodelling of Colchester to coincide with the electrification down to Chelmsford and to provide a grade seperated junction onto the Clacton line for improved direct services to London. Colchester feeder station was definately intended to supply the route northwards to Ipswich in that future scheme (which came in 1985) so they may have installed a neutral section on the main lines here in preparation for that. It is not known whether this was the case, but not especially important either way.

In terms of the information provided, the 1960/1961 Working Instructions both include diagrammatic maps of lines and stations that are electrified with TSCs, neutral sections, feeder stations and control stations marked out. However they only give general positions of those locations with details like "located near milepost 12" for TSCs and FSs only, so the exact location of the neutral section connected to the FS/TSC can only be guessed at. The 1975 source lists all neutral sections in the country at that time with a miles and feet measurement. The milages that appear in the green lables are conversions to mile and chain made out of this information and so milage is vauge where the 1975 source doesn't mention said OHNS (Bethnal Green WAML and Bishop's Stortford). Meanwhile the 1962 MoT report gives positions of neutral sections of a geographical map without any specific milage information. That map also indicates which lines were under construction at that time (Chelmsford to Colchester and LTS which technically would have opened before this document was published) and what lines were proposed to be electrified later.

In reference to railcodes.org and the sectional appendix, railcodes.org is of course unofficial, lists no sources and is occaisionly incorrect enough for my research to challenge their claims. The sectional appendix (table A is the useful part) is also innaccurate on some matters and only updates table A pages as and when meaning some parts can be quite old even if the document is re-issued every quarter. It also could be possible that information is withheld from the public releases.

Of course, lines electrified after 1975 only have the later two sources given. Lines are colour coded as to which set of schemes first electrified them:

• 1.5kv DC system of 1949-1956
  

• Liverpool Street/Fenchurch Street to Shenfield (1949, using GE/MSW OLE)

• Shenfield to Chelmsford/Southend Victoria (1956, using SCS OLE)
  

• 1959-1963 mixed voltage AC lines using BR mark 1 OLE

• Colchester to Clacton/Walton (1959, 25kv AC)

• Chenford (1960, 6.25kv AC/25kv AC)
  

• LTS lines including Forest Gate junction to Barking (1961, 6.25kv AC/25kv AC)

• Chelmsford to Colchester (1962, 25kv AC)
  

• Ockenden branch (1963, 25Kv AC)

• The previously DC lines were converted to 6.25kv AC in 1960 (Except for Shenfield to Chelmsford which was earthed from 1960 until re-energised at 25kv AC in 1962).
  

• 1969 in-fill from Clapton junction to Cheshunt via Tottenham Hale (otherwise known as the Lea Valley mainline) using mark 3 OLE at 25kv AC as with all schemes from this point onwards.
  

• Anglia East and West schemes from 1977-1988 all using mark 3 OLE

• Braintree Branch (1977), 

• Colchester to Ipswich (1985), 

• In 1986
  

• Manningtree to Harwich, 

• Southminster branch, 

• Romford to Upminster, 

• The Graham Road curve (wiring being Reading Lane Junction to Dalston Kingsland station)

• Ipswich to Stowmarket

• In 1987 

• Stowmarket to Norwich

• Bishop's Stortford to Cambridge

• Royston to Shepreth Branch Junction (1988)
  

• Then a few infill schemes in London

• Camden Road to Stratford (previously electrified with third rail) in 1988

• The map does not show this line beyond Navarino Road junction
  

• Stratford to Coppermill Junction via Lea Bridge (1989) 

• Tottenham South Junction to Seven Sisters (1989)

• Extensions to Anglia West in the 1990s

• Stansted Airport branch (1991)

• Cambridge to King's Lynn (1992)

• The small addition of Stratford platforms 1 and 2 for the new London Overground service in 2009

• Further London Overground extensions using Series 2 OLE (all schmes since 1969 had been using various subtypes of BR mark 3)

• Gospel Oak to Barking (specifically, Woodgrange Park junction to Gospel Oak although this map stops just before Harringay Green Lanes) in 2018

• Barking Riverside branch in 2022.

At a glance this does show a certain slowing down of electrification progress since privatisation. Indeed all lines in London except for Gospel Oak - Barking were wired by the 1990s so the number of obvious choices in Anglia region has been somewhat low. But it should be mentioned that the 1962 MoT report states that Felixstowe branch was definately proposed for wiring back then. In my speculation, Felixstowe to Ipswich, Stowmarket to Ely/Cambridge and Ely to Peterborough are the most likely candidates to get proposed (or reproposed) simply because of the container freight eminating from Felixstowe. Indeed, the North London Line and other inner suburban lines around Stratford were electrified in the late 1980s in order for freight flows to be accomodated from the WCML to GEML and LTS lines. I can say with some certainty that the Sudbury branch, East Suffolk line, Wherry lines and Bittern line will never be electrified - the Breckland line could believably go either way. This is also the recommendation of the oft forgotten Traction Decarbonisation Network Stratergy (interim) of 2020.

This map serves as a useful baseline reference for placing in time and space the more detailed machinations I will be investigating later. This is especially true because no other diagram I have made will show positions of stations. The yellow labled text are the Engineer's Line Reference (ELR) for each stretch of railway.

As a last note: railcodes.org and the 1975 source offer specific names for neutral sections while the sectional appendix and 1960-1962 sources do not.