British Rail Class 313
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The British Rail Class 313 is a dual-voltage
electric multiple unit An electric multiple unit or EMU is a multiple-unit train consisting of self-propelled carriages using electricity as the motive power. An EMU requires no separate locomotive, as electric traction motors are incorporated within one or a numbe ...
(EMU) train built by
British Rail Engineering Limited British Rail Engineering Limited (BREL) was the railway systems engineering subsidiary of British Rail. Established in 1970, the maintenance arm was split as British Rail Maintenance Limited in 1987, and the design and building of trains was pr ...
's
Holgate Road carriage works The Holgate Road carriage works was a railway carriage manufacturing factory in the Holgate area of York, England. The factory began production in 1884 as a planned expansion and replacement of the North Eastern Railway's Queen Street site; ...
between February 1976 and April 1977. They were the first production units that were derived from
British Rail British Railways (BR), which from 1965 traded as British Rail, was a state-owned company that operated most of the overground rail transport in Great Britain from 1948 to 1997. It was formed from the nationalisation of the Big Four British rai ...
's 1971 prototype suburban EMU design which, as the BREL 1972 family, eventually encompassed 755 vehicles over five production classes (313, 314,
315 __NOTOC__ Year 315 ( CCCXV) was a common year starting on Saturday (link will display the full calendar) of the Julian calendar. At the time, it was known as the Year of the Consulship of Constantinus and Licinianus (or, less frequently, year ...
,
507 __NOTOC__ Year 507 ( DVII) was a common year starting on Monday (link will display the full calendar) of the Julian calendar. At the time, it was known as the Year of the Consulship of Anastasius and Venantius (or, less frequently, year 1260 ...
and 508). They were the first second-generation EMUs to be constructed for
British Rail British Railways (BR), which from 1965 traded as British Rail, was a state-owned company that operated most of the overground rail transport in Great Britain from 1948 to 1997. It was formed from the nationalisation of the Big Four British rai ...
and the first British Rail units with both a
pantograph A pantograph (, from their original use for copying writing) is a mechanical linkage connected in a manner based on parallelograms so that the movement of one pen, in tracing an image, produces identical movements in a second pen. If a line dr ...
for
overhead line An overhead line or overhead wire is an electrical cable that is used to transmit electrical energy to electric locomotives, trolleybuses or trams. It is known variously as: * Overhead catenary * Overhead contact system (OCS) * Overhead equipmen ...
s and
contact shoe Electric current collectors are used by trolleybuses, trams, electric locomotives or EMUs to carry electrical power from overhead lines, electrical third rails, or ground-level power supplies to the electrical equipment of the vehicles. Those for ...
equipment for supply. They were, additionally, the first units in Britain to employ multi-function automatic Tightlock couplers, which include electrical and pneumatic connections allowing the coupling and uncoupling of units to be performed unassisted by the driver whilst in the cab. The Class 313 units are the oldest EMUs on the National Rail network, at 46 years old; they entered service in 1976 However, the even-older 1972 Stock and 1973 Stock are still in service on
London Underground The London Underground (also known simply as the Underground or by its nickname the Tube) is a rapid transit system serving Greater London and some parts of the adjacent ceremonial counties of England, counties of Buckinghamshire, Essex and He ...
.


Description

The Class 313 was developed following extensive trials with the prototype Class 445 "PEP" built in the early 1970s. The 313 is similar to the Class 314 (Glasgow), Class 315 (Anglia suburban — east London), Class 507 (Merseyside) and Class 508 (Merseyside, formerly Southern Region). The Class 313 directly replaced the Class 105 and 106 diesel multiple units previously on the Great Northern Inner Suburban services between London and Hertfordshire. Since they were designed for use on Great Northern Inner Suburban services from to , , and , which included a section of 'tube' line built to take standard size trains between and Moorgate, they are built to a slightly smaller
loading gauge A loading gauge is a diagram or physical structure that defines the maximum height and width dimensions in railway vehicles and their loads. Their purpose is to ensure that rail vehicles can pass safely through tunnels and under bridges, and ke ...
than conventional trains. They are standard length and width, but the roof is lower, most noticeable due to the lack of a "well" for the Stone Faiveley AMBR
pantograph A pantograph (, from their original use for copying writing) is a mechanical linkage connected in a manner based on parallelograms so that the movement of one pen, in tracing an image, produces identical movements in a second pen. If a line dr ...
on the centre coach. They have to comply with regulations for underground trains, such as having doors at each end of the train for evacuation onto the tracks, and when on 750 V DC supply the traction supply for each motor coach is separate, whereas on conventional 750 V DC trains each coach in a unit is linked by a 750 V bus line. Due to this, each motor coach has shoe gear on both
bogie A bogie ( ) (in some senses called a truck in North American English) is a chassis or framework that carries a wheelset, attached to a vehicle—a modular subassembly of wheels and axles. Bogies take various forms in various modes of transp ...
s, whereas normally it would only be on the leading bogie. They are fitted with trip-cocks that are struck by a raised train-stop arm at red signals and will apply the brakes if the train passes one. The units were originally numbered 313001–313064. Each unit is formed of two outer driving motors and an intermediate trailer with a pantograph. This is a reversal of the practice started in the 1960s, where the motors and pantograph were on an intermediate vehicle, with the outer vehicles being driving trailers. Part of the reason was to simplify the equipment to allow dual-voltage operation, and to keep down weight by spreading the heavy transformer and motors between vehicles. The intermediate trailer carries the pantograph and a
transformer A transformer is a passive component that transfers electrical energy from one electrical circuit to another circuit, or multiple circuits. A varying current in any coil of the transformer produces a varying magnetic flux in the transformer' ...
and
rectifier A rectifier is an electrical device that converts alternating current (AC), which periodically reverses direction, to direct current (DC), which flows in only one direction. The reverse operation (converting DC to AC) is performed by an Power ...
, which on 25 kV AC provides 750 V DC to the motor coaches, each of which has four GEC G310AZ
direct current Direct current (DC) is one-directional flow of electric charge. An electrochemical cell is a prime example of DC power. Direct current may flow through a conductor such as a wire, but can also flow through semiconductors, insulators, or even ...
traction motor A traction motor is an electric motor used for propulsion of a vehicle, such as locomotives, electric vehicle, electric or hydrogen vehicles, elevators or electric multiple unit. Traction motors are used in electrically powered rail vehicles (ele ...
s, two per bogie. On 750 V DC each motor coach draws its supply directly through its shoe gear. The traction motors are driven by a
camshaft A camshaft is a shaft that contains a row of pointed cams, in order to convert rotational motion to reciprocating motion. Camshafts are used in piston engines (to operate the intake and exhaust valves), mechanically controlled ignition systems ...
-controlled resistance system with series and parallel motor groupings and weak field steps. Originally the heating in the motor coaches was provided by passing air over the hot traction and braking
resistors A resistor is a passive two-terminal electrical component that implements electrical resistance as a circuit element. In electronic circuits, resistors are used to reduce current flow, adjust signal levels, to divide voltages, bias active el ...
in addition to conventional heaters, but this feature is no longer in use and the pneumatic dampers have been disabled. Great Northern and Southern retrofitted their units with cab air conditioning. 313s have
rheostatic braking Dynamic braking is the use of an electric traction motor as a generator when slowing a vehicle such as an electric or diesel-electric locomotive. It is termed " rheostatic" if the generated electrical power is dissipated as heat in brake grid ...
(which was disabled on London Overground) in addition to conventional three-step air-operated disc braking. During braking if wheelslide is detected by the
Wheel slide protection Wheel slide protection and wheel slip protection are railway terms used to describe automatic systems used to detect and prevent wheel-slide during braking or wheel-slip during acceleration. This is analogous to ABS and traction control systems us ...
(WSP), rheostatic braking is disabled and disc-braking only is used. Great Northern units had sanding equipment. Unlike some other DMU/EMU classes, additional brake force is not available when the emergency brake application is initiated and is the equivalent force of a step 3/full service application. WSP is still active when making an emergency application. In addition to the primary
suspension Suspension or suspended may refer to: Science and engineering * Suspension (topology), in mathematics * Suspension (dynamical systems), in mathematics * Suspension of a ring, in mathematics * Suspension (chemistry), small solid particles suspend ...
of rubber chevron spring and oil dampers, secondary suspension is provided by two air bellows per bogie - flow into each bellows is controlled independently by a levelling valve and arm assembly that allows the suspension to inflate/deflate when the weight of the coach is increased or decreased by passenger loading. The air suspension is linked to the braking system via a Variable Load Valve (VLV), which increases air brake pressure when the coach is more heavily loaded to compensate for the additional weight. Vehicles are numbered as follows. * 62529–62592: DMSO (Driver's cab, Motor car, Standard class, Open saloon) * 71213–71276: PTSO (Pantograph, Trailer car, Standard class, Open saloon) * 62593–62656: BDMSO (Battery for auxiliaries, Driver's cab, Motor car, Standard class, Open saloon) All units have standard class seating only. As built, the sliding doors were opened by the passengers. Once the driver had stopped the train and the guard had activated the master door release, a passenger could move the door handle gently sideways which operated a switch controlling the individual door opening circuit. Many people did not wait for the guard's release and gave the handle a much harder tug, which could open the door even if the train had not stopped. Concerns over passenger safety led to the handles being replaced by push-buttons from March 1977. Modifications led to renumbering and reclassification. All units originally had shoebeams on the inner bogie of each motor coach, which was sufficient for third-rail duties between Drayton Park and Moorgate. Some units became surplus, and in 1987 four were transferred to the Clacton/
Walton Walton may refer to: People * Walton (given name) * Walton (surname) * Susana, Lady Walton (1926–2010), Argentine writer Places Canada * Walton, Nova Scotia, a community ** Walton River (Nova Scotia) *Walton, Ontario, a hamlet United Kingdo ...
route, which has no DC sections; they had the shoegear removed, and were renumbered from 313061–313064 to 313096–313099. Following an accident involving one unit at Walton-on-the-Naze in August 1987, they were replaced by units in 1988. Units 313001–313016 had shoegear fitted to the outer bogies in addition, and were transferred to the Watford DC route where there are long gaps in the third rail. They were renumbered into a new 313/1 subclass, leaving the unmodified units in subclass 313/0. Following the
privatisation of British Rail The privatisation of British Rail was the process by which ownership and operation of the railways of Great Britain passed from government control into private hands. Begun in 1994, it had been completed by 1997. The deregulation of the industr ...
, ownership of the Class 313 fleet passed to leasing company
Eversholt Rail Group Eversholt Rail Group is a British rolling stock company (ROSCO). Together with Angel Trains and Porterbrook, it is one of the three original ROSCOs created as a result of the privatisation of British Rail. Eversholt was established in March 1994 ...
. In June 2012 Eversholt sold twenty units (313121 and the nineteen 313/2 units) to newly formed lessor
Beacon Rail Beacon Rail is a rolling stock company (ROSCO) based in the United Kingdom. Its primary business is the leasing of locomotives and rolling stock to various train operating companies (TOCs). The company originated within Allco Finance Group's Eur ...
.


Operations


Current


Southern (Govia Thameslink Railway)

Nineteen 313s displaced by ''Capitalstars'' on London Overground have been transferred to Southern, replacing the newer Class 377/3 ''Electrostars'' on
East East or Orient is one of the four cardinal directions or points of the compass. It is the opposite direction from west and is the direction from which the Sun rises on the Earth. Etymology As in other languages, the word is formed from the fa ...
and West Coastway services from . They primarily operate local services from Brighton to , , , and Seaford. In addition, they work the to and services. These units were repainted at
Wolverton Works Wolverton railway works, known locally as Wolverton Works or just The Works, was established in Wolverton, Buckinghamshire, by the London and Birmingham Railway Company in 1838 at the midpoint of the route from London to Birmingham. The line w ...
and renumbered from 313/1 into a new 313/2 subclass. The full refurbishment began in June 2010 at Wabtec Doncaster and included new flooring and carpet, new seating, improved space for cycles and passengers in wheelchairs, and the fitting of a
Passenger Information System A passenger information system, or passenger information display system, is an automated system for supplying users of public transport with information about the nature and the state of a public transport service through visual, voice or other m ...
. Additional modifications were carried out at
Stewarts Lane TMD Stewarts Lane is a large railway-servicing facility in Battersea in London, England, founded by the London Chatham and Dover Railway (LCDR) in 1862, to serve London Victoria railway station. It is sited in the midst of a maze of railway lines ...
including the installation of cab air-conditioning, sanding equipment, a 750 V busline, shore supply sockets and the removal of overhead line equipment. The 313s commenced operations with Southern on 23 May 2010, providing a two-trains-per-hour service between Brighton and Seaford, and some trains between Brighton and , , and . From 13 December 2010, their operation expanded to stopping services from Brighton to and the to shuttle. The decision to use 313s on the Coastway lines has been controversial, as they are much older than the 377s and have fewer on-board passenger facilities. The rail union RMT criticised the move and many publications, including the BBC, have questioned the introduction of 35-year-old trains in place of much newer units. These trains are deployed on services that operate predominantly over short distances, such as Brighton to Hove and Brighton to Seaford, and some longer (but stopping) services that provide predominantly local links that run alongside 377s on faster services. The introduction of 313s on the Coastway routes facilitated the delivery of additional capacity on high-demand suburban routes in South London, where 10-car trains services are to be introduced combined with platform lengthening. In December 2017, it was announced that unit 313201—originally 313001, the first and oldest Class 313 unit—had been repainted into British Rail's Rail Blue livery, as originally used on the units (though, to meet today's accessibility requirements, the passenger doors were painted entirely grey rather than blue and grey as original). The repaint was part of the C6 overhaul, which included works on the doors, air system and interior, which includes new, modern LED lighting, and for bodywork repairs. The Director of Engineering for Beacon Rail, which owns the Class 313s, has said, "We wanted to celebrate the heritage of this special train, so the re-livery made perfect sense."


Former


Silverlink/London Overground

Silverlink Silverlink was a train operating company in the United Kingdom owned by National Express that operated the North London Railways franchise from March 1997 until November 2007. At the end of 2007 Silverlink Metro services were taken over by Lond ...
inherited 23 units from British Rail. These were mainly operated under the Silverlink Metro brand on the
North London North London is the northern part of London, England, north of the River Thames. It extends from Clerkenwell and Finsbury, on the edge of the City of London financial district, to Greater London's boundary with Hertfordshire. The term ''nort ...
,
West London West London is the western part of London, England, north of the River Thames, west of the City of London, and extending to the Greater London boundary. The term is used to differentiate the area from the other parts of London: North London ...
, and Watford DC lines, although they were also regularly used on the St Albans AbbeyWatford Junction branch line between 1988 and the end of the Silverlink franchise in 2007. In 2007 they were used on services transferred to
London Overground London Overground (also known simply as the Overground) is a Urban rail in the United Kingdom, suburban rail network serving London and its environs. Established in 2007 to take over Silverlink Metro routes, (via archive.org). it now serves a ...
, which replaced Silverlink Metro. London Overground branding was added, and some seats were removed to provide additional standing room. They were replaced by Class 378 trains, with longitudinal seating to improve standing room. The final day of scheduled 313 operation on the North and West London Lines was 19 February 2010, although units remained in use as ad-hoc substitutes for unavailable 378/0s. By August 2010 only 313121 and 313123 were still in service with London Overground, as the 378/2 ''Capitalstars'' were by then in use on the Watford DC Line. They last ran for London Overground on 13 September 2010.


West Anglia Great Northern/First Capital Connect/Great Northern (Govia Thameslink Railway)

West Anglia Great Northern West Anglia Great Northern, commonly shortened to ''WAGN'', was a train operating company in England. It operated the West Anglia Great Northern franchise between January 1997 and March 2004, as well as the Great Northern franchise between Apri ...
inherited 41 units operating inner suburban services out of
Moorgate Moorgate was one of the City of London's northern gates in its defensive wall, the last to be built. The gate took its name from the Moorfields, an area of marshy land that lay immediately north of the wall. The gate was demolished in 1762, b ...
and , to , , , and . From 1 April 2006 the Great Northern (GN) franchise merged with
Thameslink Thameslink is a 24-hour main-line route in the British railway system, running from , , , and via central London to Sutton, , , Rainham, , , , and . The network opened as a through service in 1988, with severe overcrowding by 1998, carrying m ...
to form the Thameslink Great Northern franchise, which was won by
FirstGroup FirstGroup plc is a British multi-national transport group, based in Aberdeen, Scotland.First Capital Connect First Capital Connect (FCC) was a British train operating company, owned by FirstGroup, that operated the Thameslink and Great Northern sectors from April 2006 to September 2014 which later became the Thameslink, Southern and Great Northern (T ...
. Three Class 313/1 units were transferred to First Capital Connect from London Overground in September 2010 to augment the Class 313/0 fleet. They were repainted into FCC livery and lightly refreshed internally but retained their original low-backed seating. Despite receiving modifications that made them mechanically identical to the 313/0s, they were not renumbered. The units were then transferred to
Great Northern Great Northern may refer to: Transport * One of a number of railways; see Great Northern Railway (disambiguation). * Great Northern Railway (U.S.), a defunct American transcontinental railroad and major predecessor of the BNSF Railway. * Great ...
on 14 September 2014 when the Thameslink and Great Northern franchise was merged into the
Thameslink, Southern and Great Northern Thameslink, Southern and Great Northern (TSGN) is a management contract for the provision of passenger services on the Thameslink and Great Northern routes to , , , , , , London Moorgate, Sutton, Wimbledon and Brighton, as well as the whole S ...
franchise. Although the majority of the route is
overhead line An overhead line or overhead wire is an electrical cable that is used to transmit electrical energy to electric locomotives, trolleybuses or trams. It is known variously as: * Overhead catenary * Overhead contact system (OCS) * Overhead equipmen ...
equipment, the
Northern City Line The Northern City Line is a commuter railway line in England, which runs from Moorgate station to Finsbury Park in London with services running beyond. It is part of the Great Northern Route services, and operates as the south-eastern branc ...
route between Moorgate and is , formerly part of the London Underground's
Northern line The Northern line is a London Underground line that runs from North London to South London. It is printed in black on the Tube map. The Northern line is unique on the Underground network in having two different routes through central London, two ...
, and although built to full loading gauge there is insufficient clearance to add catenary. Trains bound for Moorgate approach Drayton Park on a falling gradient, drawing power via the pantograph. After coming to a stand at the platform the driver opens the vacuum circuit breaker, lowers the pantograph and changes over to DC. Whilst at Drayton Park, the starting signal for the platform is held at danger until the pantograph is lowered. Unusually for dual voltage trains, on this stock and its replacement, the Class 717, a shunt resistor is permanently connected to the pantograph. The detection of the small current drawn holds the signal at danger while the pantograph remains in contact with the overhead wire. This current is very audible as it manifests itself as a distinct buzzing noise as an arc is struck and subsequently extinguished as the pantograph lowers. This prevents the driver from powering into the tunnel with the pantograph raised which would cause damage to the train as the pantograph ran off the end of the overhead line and struck the tunnel portal. On journeys from Moorgate traction power is maintained into Drayton Park for the rising gradient. Once the train is at a stand the driver selects AC traction and raises the pantograph. There is no system forcing the driver to change traction supplies beyond the customary 'PANS UP' sign at the end of the platform. If the driver forgets to change to AC no damage will occur to the train or any infrastructure; there will simply be a loss of power as the train runs out of third rail. Great Northern 313s were electrically limited to in DC mode, the maximum line speed on the Northern City Line. 313134 was named "City of London" at Moorgate on 9 December 2010 by Michael Bear, the
Lord Mayor of London The Lord Mayor of London is the mayor of the City of London and the leader of the City of London Corporation. Within the City, the Lord Mayor is accorded precedence over all individuals except the sovereign and retains various traditional powe ...
. The final Class 313 service on Great Northern was the 23:33 Hertford North to Moorgate on 30 September 2019. A final railtour, operating from London King's Cross to Royston (via Welwyn Garden City) and back (via Hertford North and Moorgate) was held on 23 October 2019 with units 313134 and 313064; the DMSO vehicle of 313064 was repainted in
Network SouthEast Network SouthEast (NSE) was one of the three passenger sectors of British Rail created in 1982. NSE mainly operated commuter rail trains within Greater London and inter-urban services in densely populated South East England, although the netwo ...
livery.


Departmental use

Network Rail leased Beacon Rail-owned unit 313121 as a test vehicle for the
European Rail Traffic Management System The European Rail Traffic Management System (ERTMS) is the system of standards for management and interoperation of signalling for railways by the European Union (EU). It is conducted by the European Union Agency for Railways (ERA) and is the o ...
(ERTMS) installation on the Hertford Loop. The unit was repainted into Network Rail's yellow house colours and internally refurbished at
Alstom Alstom SA is a French multinational rolling stock manufacturer operating worldwide in rail transport markets, active in the fields of passenger transportation, signalling, and locomotives, with products including the AGV, TGV, Eurostar, Avelia ...
's
Wembley Intercity Depot Wembley Intercity Depot (alternatively, Wembley Brent Depot) is an Electric Traction Depot located in Wembley, London Borough of Brent, England. The depot is situated alongside Wembley Yard, on the eastern side of the West Coast Main Line, to ...
, to include a new driving desk, technician's workstation, kitchen and toilet facilities, and the necessary ERTMS equipment. The work was completed in June 2013 and the unit was tested for the first time on Friday 5 July 2013 between Wembley and . It commenced testing on the Hertford Loop later that month. Following conclusion of the Hertford Loop works, it was placed in store at
Eastleigh Works Eastleigh Works is a locomotive, carriage and wagon building and repair facility in the town of Eastleigh, in the county of Hampshire in England. History LSWR The London and South Western Railway (LSWR) opened a carriage and wagon works at Eas ...
in May 2018. It will be returned to service when ERTMS is ready for testing on the
Great Western Main Line The Great Western Main Line (GWML) is a main line railway in England that runs westwards from London Paddington to . It connects to other main lines such as those from Reading to Penzance and Swindon to Swansea. Opened in 1841, it was the or ...
.


Replacement

The Great Northern fleet has been replaced by new six-carriage Class 717s. The transition commenced on 25 March 2019, with the first two 717s entering service. The first of the Great Northern fleet withdrawn was 313026 in February 2019. It was the first dispatched for scrapping in April 2019. All 44 of the Great Northern 313s have since been withdrawn and scrapped. Upon retirement 313201 will be preserved by the
National Railway Museum The National Railway Museum is a museum in York forming part of the Science Museum Group. The museum tells the story of rail transport in Britain and its impact on society. It is the home of the national collection of historically significant r ...
. The Southern Class 313s are expected to be withdrawn at the May 2023 timetable change.


Accidents and incidents

* On 15 October 1986, unit 313012 ran into the rear of a
London Underground The London Underground (also known simply as the Underground or by its nickname the Tube) is a rapid transit system serving Greater London and some parts of the adjacent ceremonial counties of England, counties of Buckinghamshire, Essex and He ...
empty stock train at due to excessive speed after passing a signal at caution. Twenty-five people were injured. * On 12 August 1987, unit 313063 overran the
buffer stop A buffer stop, bumper, bumping post, bumper block or stopblock (US), is a device to prevent railway vehicles from going past the end of a physical section of track. The design of the buffer stop is dependent, in part, on the kind of couplings ...
at and demolished the station building due to a brake fault on the train. Thirteen people were injured. * On 22 October 2020, unit 313212 was derailed at due to a signalling error. * On 19 November 2020, unit 313220 was involved in a fire at station. * On 10 March 2021, unit 313203 was involved in a fire at station.


Fleet details


Named units

Named units were as follows: * 313020 – ''
Parliament Hill Parliament Hill (french: Colline du Parlement, colloquially known as The Hill, is an area of Crown land on the southern banks of the Ottawa River in downtown Ottawa, Ontario, Canada. Its Gothic revival suite of buildings, and their architectu ...
'' (denamed) * 313054 – ''Captain William Leefe Robinson V.C.'' (unit scrapped) * 313101 – ''
Silvertown Silvertown is a district in the London Borough of Newham, in east London, England. It lies on the north bank of the River Thames, Thames and was historically part of the parishes of West Ham and East Ham, Becontree Hundred, hundred of Becontr ...
'' (denamed) * 313109 – ''Arnold Leah'' (denamed) * 313111 – ''
London TravelWatch London TravelWatch is a statutory British consumer organisation that campaigns for improvements to transport in London. It deals with all complaints from passengers using any Transport for London modes including some cycling and pedestrian issu ...
'' (denamed) * 313116 – ''
Nikola Tesla Nikola Tesla ( ; ,"Tesla"
''
The Hackney Empire'' (denamed); ''
City of London The City of London is a city, ceremonial county and local government district that contains the historic centre and constitutes, alongside Canary Wharf, the primary central business district (CBD) of London. It constituted most of London fr ...
'' (unit scrapped)


Notes


References


Further reading

* * {{British Rail EMU 313 313 Train-related introductions in 1976 750 V DC multiple units 25 kV AC multiple units