This article lists every electric-powered multiple unit allocated a TOPS classification or used on the mainline network since 1948 (i.e. British Railways and post-privatisation). For a historical overview of electric multiple unit development in Great Britain, see British electric multiple units. British Rail operated a wide variety of electric multiple units for use on electrified lines: * AC units operate off 25 kV alternating current (AC) from overhead wires. Where clearances for the overhead wires on the Great Eastern Main Line and London, Tilbury and Southend railway routes were below standard, a reduced voltage of 6.25 kV AC was used. The Midland Railway units used 6.6 kV AC. Under the computer numbering, AC units (including mixed-voltage units that can also work off a DC supply) were given a class in the range 300-399. * DC units operate off 650-850 V direct current (DC) from a third rail on the Southern Region and North London, Merseyside and Tyneside networks. The Manchester-Bury Railway line used 1,200 V DC from a side-contact third rail. The Manchester South Junction & Altrincham and "Woodhead" and initially the Great Eastern Railway routes used 1,500 V DC from overhead wires. Under the computer numbering, DC units were given a class in the range 400-599. (en)