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British Rail Class 313
The British Rail Class 313 is a class of dual-voltage electric multiple units (EMU) suburban and regional passenger trains. Built by British Rail Engineering Limited at Holgate Road carriage works between February 1976 and April 1977, they were the first production units that were derived from British Rail's 1971 prototype suburban EMU design which, as the BREL 1972 family, eventually encompassed 755 vehicles over five production classes (313, 314, 315, 507 and 508). They were the first second-generation EMUs to be constructed for British Rail and the first British Rail units with both a pantograph for 25 kV 50 Hz AC overhead lines and contact shoe equipment for 750 V DC third rail 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 were the oldest EMUs operating on the National Rail network in Great Britain prior to their withdrawal in 2023, having entered service in 1976. However, the even older 1972 Stock and 1973 Stock are still in service on London Underground.
Two new fleets were ordered as part of the electrification, authorised in 1971, of suburban services on British Rail's Great Northern route between London King's Cross and Royston, via Welwyn Garden City on the East Coast Main Line and via Hertford North on the Hertford Loop Line. For outer-suburban services – those making limited stops over the length of the route – a fleet of 49 Class 312 units were procured as derivatives of the proven Class 310 design. The Class 313 fleet was correspondingly ordered for the inner-suburban services – those making frequent stops between London and Welwyn or Hertford.
An integral component of the electrification programme was BR's acquisition from London Underground of the Northern City Line, which had been built at a size sufficient for mainline trains and which provided the most direct route between Finsbury Park, on the existing Great Northern route, and Moorgate in the City of London. Following completion of the electrification to Welwyn and Hertford, the London terminal for all inner-suburban services would switch from King's Cross to Moorgate, reducing the number of train movements at the former station enough to permit the remodelling and subsequent electrification of the complicated approach tracks. The Northern City Line tunnels, however, were still not large enough to be fitted with the same 25 kV 50 Hz AC overhead line electrification system used for the rest of programme, and were instead configured to use the 750 V DC third rail system standard on BR's Southern Region. This in turn required that a new design of EMU be developed for the Class 313 order, as none capable of running on both systems existed at the time.
Given this requirement, the opportunity was taken to further develop the Class 445 and 446 prototypes that had been produced by British Rail Engineering Limited in 1971, and which were considered by BR to be "the basis of all [its] future suburban stock". As these prototypes had been configured for use only on third-rail electrification, a new intermediate trailer carrying a pantograph and AC to DC transformer was built and inserted into the two-car Class 446 prototype, which was then tested on AC-electrified track for six months in 1975. This three-car arrangement, with driving-motor vehicles 'sandwiching' the trailer carrying the AC collection equipment, was subsequently adopted as the basic layout for the Class 313 design.
Given the need to use the Northern City Line tunnels, Class 313 units were built to a slightly smaller loading gauge than conventional trains. They were of standard length and width, but the roof was lower, which was most noticeable due to the lack of a "well" for the Stone Faiveley AMBR pantograph on the centre coach. They had 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 was 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 had shoe gear on both bogies, whereas normally it would only be on the leading bogie. They were 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 was formed of two outer driving motors and an intermediate trailer with a pantograph. This was 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 carried the pantograph and a transformer and rectifier, which on 25 kV AC provides 750 V DC to the motor coaches, each of which had four 110 horsepower (82 kW) GEC G310AZ direct current traction motors, two per bogie. On 750 V DC each motor coach drew its supply directly through its shoe gear. The traction motors were driven by a camshaft-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 in addition to conventional heaters, but this feature was later taken out of use and the pneumatic dampers were disabled. Great Northern and Southern retrofitted their units with cab air conditioning.
313s had rheostatic braking (which was disabled on London Overground) in addition to conventional three-step air-operated disc braking. During braking if wheelslide was detected by the Wheel slide protection (WSP), rheostatic braking was disabled and disc-braking only was used. Great Northern units had sanding equipment. Unlike some other DMU/EMU classes, additional brake force was not available when the emergency brake application was initiated and was the equivalent force of a step 3/full service application. WSP was still active when making an emergency application.
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British Rail Class 313
The British Rail Class 313 is a class of dual-voltage electric multiple units (EMU) suburban and regional passenger trains. Built by British Rail Engineering Limited at Holgate Road carriage works between February 1976 and April 1977, they were the first production units that were derived from British Rail's 1971 prototype suburban EMU design which, as the BREL 1972 family, eventually encompassed 755 vehicles over five production classes (313, 314, 315, 507 and 508). They were the first second-generation EMUs to be constructed for British Rail and the first British Rail units with both a pantograph for 25 kV 50 Hz AC overhead lines and contact shoe equipment for 750 V DC third rail 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 were the oldest EMUs operating on the National Rail network in Great Britain prior to their withdrawal in 2023, having entered service in 1976. However, the even older 1972 Stock and 1973 Stock are still in service on London Underground.
Two new fleets were ordered as part of the electrification, authorised in 1971, of suburban services on British Rail's Great Northern route between London King's Cross and Royston, via Welwyn Garden City on the East Coast Main Line and via Hertford North on the Hertford Loop Line. For outer-suburban services – those making limited stops over the length of the route – a fleet of 49 Class 312 units were procured as derivatives of the proven Class 310 design. The Class 313 fleet was correspondingly ordered for the inner-suburban services – those making frequent stops between London and Welwyn or Hertford.
An integral component of the electrification programme was BR's acquisition from London Underground of the Northern City Line, which had been built at a size sufficient for mainline trains and which provided the most direct route between Finsbury Park, on the existing Great Northern route, and Moorgate in the City of London. Following completion of the electrification to Welwyn and Hertford, the London terminal for all inner-suburban services would switch from King's Cross to Moorgate, reducing the number of train movements at the former station enough to permit the remodelling and subsequent electrification of the complicated approach tracks. The Northern City Line tunnels, however, were still not large enough to be fitted with the same 25 kV 50 Hz AC overhead line electrification system used for the rest of programme, and were instead configured to use the 750 V DC third rail system standard on BR's Southern Region. This in turn required that a new design of EMU be developed for the Class 313 order, as none capable of running on both systems existed at the time.
Given this requirement, the opportunity was taken to further develop the Class 445 and 446 prototypes that had been produced by British Rail Engineering Limited in 1971, and which were considered by BR to be "the basis of all [its] future suburban stock". As these prototypes had been configured for use only on third-rail electrification, a new intermediate trailer carrying a pantograph and AC to DC transformer was built and inserted into the two-car Class 446 prototype, which was then tested on AC-electrified track for six months in 1975. This three-car arrangement, with driving-motor vehicles 'sandwiching' the trailer carrying the AC collection equipment, was subsequently adopted as the basic layout for the Class 313 design.
Given the need to use the Northern City Line tunnels, Class 313 units were built to a slightly smaller loading gauge than conventional trains. They were of standard length and width, but the roof was lower, which was most noticeable due to the lack of a "well" for the Stone Faiveley AMBR pantograph on the centre coach. They had 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 was 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 had shoe gear on both bogies, whereas normally it would only be on the leading bogie. They were 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 was formed of two outer driving motors and an intermediate trailer with a pantograph. This was 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 carried the pantograph and a transformer and rectifier, which on 25 kV AC provides 750 V DC to the motor coaches, each of which had four 110 horsepower (82 kW) GEC G310AZ direct current traction motors, two per bogie. On 750 V DC each motor coach drew its supply directly through its shoe gear. The traction motors were driven by a camshaft-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 in addition to conventional heaters, but this feature was later taken out of use and the pneumatic dampers were disabled. Great Northern and Southern retrofitted their units with cab air conditioning.
313s had rheostatic braking (which was disabled on London Overground) in addition to conventional three-step air-operated disc braking. During braking if wheelslide was detected by the Wheel slide protection (WSP), rheostatic braking was disabled and disc-braking only was used. Great Northern units had sanding equipment. Unlike some other DMU/EMU classes, additional brake force was not available when the emergency brake application was initiated and was the equivalent force of a step 3/full service application. WSP was still active when making an emergency application.