An electric multiple unit (EMU) is an electric self-powered train, capable of operating in multiple with other EMUs and without the need for a locomotive; these are typically passenger trains with accommodation in every vehicle and a driving position at each end. The term can also be used to describe a train that is a permanent formation with a non-driving power car, such as the Advanced Passenger Train. , two-thirds of the passenger carriages in Great Britain are formed in EMUs.
Electric railways began in Great Britain in 1883 and the first EMU ran on the Liverpool Overhead Railway in 1893. In the early 20th century, systems were developed where all the motors on a train could be controlled by a low voltage signal from any cab. Due to problems using steam locomotives underground, the underground railways in London and Liverpool were early adopters of electric traction and, by 1907, underground railways in London and some provincial cities were running electric trains. A 6.7 kV 25 Hz overhead system was also used from 1908. After the railway companies were grouped in 1923, the Southern Railway greatly expanded the third-rail DC electrification, replacing some early AC electrification. Overhead lines at were planned and installed just before and after the Second World War. The early EMU carriages, similar to contemporaneous locomotive-hauled carriages, were constructed of wood with hinged doors with accommodation in saloons or compartments. As time went on, more steel became used in carriage construction.
After the Second World War, the railways were nationalised and the overhead system was installed; this eventually replaced all systems. South of London, the Southern Railway third-rail electrification system continued to expand.
Origins Early electric railways
Volks Electric Railway, the first electric passenger railway in Britain, opened in 1883 as a short gauge electric railway running for in Brighton. At first electrical power at 160 V DC was supplied to a small car using the two running rails, but it was not long before a third live rail was added, a sliding shoe making contact to the top.
The City and South London Railway, a deep-level tube railway, opened in 1890 with carriages hauled by electric locomotives powered from a third rail beneath the train energised at 500 V DC. In 1893 the Liverpool Overhead Railway opened with two lightweight passenger cars coupled together; on each car one bogie was powered with a single motor powered from a third rail between the tracks at 500 V DC. Any number could be coupled together and all the motors controlled by the driver at the front.
In 1898, the deep-level Waterloo and City Railway opened with EMUs, a central third rail providing traction current at 500 V to 530 V DC. The current for the two motor cars could be controlled from either driving cab, but the Board of Trade became concerned about the fire risk presented by the 11 power cables carried on the roof of the train and barred installation of similar systems in deep-level tubes. Therefore, when in 1900 the Central London Railway opened its deep-level tube railway, electric locomotives hauled carriages.
In 1900, the Metropolitan Railway and the District Railway ran an experimental EMU in passenger service for six months. A four-rail system was used, two rails outside the running rails providing the traction current at 500–550 V DC. Only the traction motors in the leading motor car were used, the trailing motor coasting. In 1901, a Metropolitan and District joint electrification committee recommended a three-phase AC system with overhead wires. Initially this was accepted by both parties, but the District needed to raise finance and found an investor in 1901, the American Charles Yerkes. Yerkes soon had control of the District and his experiences in the United States led him to favour DC with a track level conductor rail pickup similar to that in use on the City & South London Railway and Central London Railway. After arbitration by the Board of Trade the DC system was taken up.
Low-voltage multiple control In 1897, Frank J. Sprague demonstrated a system where a low-voltage control signal from any driving position controlled all the motors on a train, developed for the South Side Elevated Railroad in Chicago. This electro-magnetic system was developed in Britain by British Thomson-Houston (BTH) and first used in Europe in 1902 on the Central London Railway when it changed over to EMU operation to solve a design problem with its locomotives. Westinghouse Electrical developed an electro-pneumatic multiple unit system that used a lower control current and when in 1903 the District opened its line from to South Harrow with experimental EMUs these used control systems from BTH and Westinghouse. After these trials the District selected BTH equipment for its B Stock.
The underground Mersey Railway started an electric service on 3 May 1903, electrified by British Westinghouse Electric with equipment from the US. A four-rail DC system was installed, with a positive outer rail and a negative return rail between the running rails.
In London, the Great Northern & City Railway was a underground line from to . EMUs with BTH electrical equipment were used from the opening on 14 February 1904; these picked up traction current from conductor rails both sides of the running rails.
When the Lancashire and Yorkshire Railway (L&YR) was considering electrification of its Liverpool suburban railways, concerns were being expressed, especially in the railway press, that engineering developments in Britain were being overtaken by electrification projects in America and Switzerland. The Preston-based Dick, Kerr & Co. was made responsible for the traction systems and the L&YR built the rolling stock. A 625 V DC four-rail system was adopted, the live rail outside the running rails with a return rail, cross-bonded to the running rails, between them. The two driving motor cars each powered by four 150 hp (110 kW) motors directly controlled from a driving cab at either end of the train. Electric services started between and on 22 March 1904.
The North Eastern Railway (NER) began using EMUs between and on 29 March 1904 and from 25 July 1904 over a circular route between and Tynemouth, electrified with a third rail at 600 V DC (see Tyneside Electrics). The EMUs, with BTH electrical equipment, were built at the NER Carriage Works at York with clerestory roofs.
The Metropolitan Railway began its electric services from Uxbridge to Baker Street in 1905 with EMUs using Westinghouse electric equipment; these ran off-peak as three-car units with a motor car and a driving trailer. Twenty trains with BTH equipment were ordered for the Hammersmith & City line, jointly operated by the Great Western Railway and the Met. From June 1905 to the end of 1905 EMUs replaced steam on all District services. In 1906-07 three deep-level tube railways opened: the Charing Cross, Euston and Hampstead Railway, Great Northern, Piccadilly and Brompton Railway and Baker Street and Waterloo Railway, all subsidiary companies of the Underground Electric Railways Company of London. The trains were built by different manufacturers to a similar design. Accommodation in open saloons was accessed by end platforms protected by lattice gates and power was collected from a 550-600 V DC four-rail system and controlled with BTH equipment.
Early overhead AC electrification
In 1908, the Midland Railway introduced EMUs that used overhead line energised at 6.7 kV 25 Hz AC, on its Heysham–Morecambe–Lancaster line. From 1909, the London, Brighton and South Coast Railway (LB&SCR) also used overhead line at 6.7 kV 25 Hz. The first section to be electrified was the South London Line connecting London Bridge with Victoria via , opened on 1 December 1909. The service was marketed as 'The Elevated Electric' and was an immediate success. By 1921 most of the inner London suburban lines were electrified and services to and Sutton opened on 1 April 1925.
The LB&SCR built three types of stock the initial South London (SL) stock was introduced as three-car trains, but after 1910 the first class trailers were removed and subsequently ran in two, four or six-car formations. In 1910 the CP stock was built for the Crystal Palace route; these normally ran as three-car units. The later five-car CW stock had motors fitted in driving motor luggage vans, passenger accommodation being in trailer cars.
From 1913 to 1916, the L&YR operated an experimental electric service in the Manchester area between Bury and Holcombe Brook. The equipment was provided by Dick, Kerr & Co., which was developing its products for overseas sales. The system used was 3.5 kV DC overhead and two two-car units were built. After these trials, the L&YR electrified the Manchester to Bury line using 1200 V DC with four rails. This opened in 1916 and in 1918 the branch to Holcombe Brook was converted to the same system.
In 1907, the London & North Western Railway (L&NWR) obtained permission for a pair of extra tracks for suburban services beside its main line from Euston to Watford. Connection with the Bakerloo line at Queen's Park was planned with through running of Bakerloo line trains, so the new tracks were electrified using the 630 V DC four-rail system used on the Bakerloo. Delayed by the World War I, the first electric service ran in 1914 from to , using borrowed District Railway trains. The L&NWR began running electric services from Broad Street to Watford in 1917 and from Euston in 1922. The first trains used electrical equipment from Siemens in Germany, but the following ones used Swiss Oerlikon equipment. The EMUs were three cars, formed from a driving motor car, trailer and a driving trailer.
From 1915, the London and South Western Railway introduced EMUs on suburban routes using a 660 V DC third-rail system. Using converted steam-hauled carriages, three-car units ran with a trailer between two driving motor cars with Westinghouse electrical equipment. After 1920, two-car trailer sets were used between these units to lengthen peak services to eight cars.
In 1921, new trains were introduced on the Underground's Piccadilly line with air-operated sliding doors. Between 1923 and 1934, Standard stock with air-operated doors replaced gate stock on London's deep-level tube railways, improving access to the cars so reducing boarding times.
Grouping In 1923, the main line railways in Britain were grouped into four companies. South of London the Southern Railway took over route miles () of railway electrified with overhead line at 6.7 kV, 57 route miles () with a third rail at , and the long underground Waterloo & City Railway. The route mileage of third rail electrification was to more than double in 1925, with routes to Guildford, and and from Victoria and to via and the Catford Loop. In 1926 EMUs started to run on the South Eastern Main Line route to Orpington and the three lines to using the third rail system.
In 1926, the Southern announced that the DC system was to replace the LB&SCR AC system, the last AC train running on 29 September 1929. Including the London Bridge to East Croydon route which was electrified in 1928, by the end of 1929 the Southern operated over route miles () of third rail electrified track and in that year ran 17.8million electric train miles.