The Class 377 Electrostar is a British electric multiple-unit train (EMU) built by Bombardier Transportation at its Derby Litchurch Lane Works, from 2001 to the present. The Electrostar family is the most numerous type of EMU built in the post-privatisation period of Britain's railways.

The class forms the major part of the Govia Thameslink Railway (GTR) fleet for Southern services and now also supplement some Southeastern services. They are primarily seen on services in the south of England.


The units work suburban services in South London, and main line commuter services to Sussex, Surrey, Kent and the South Coast, on which they replaced 4Cig and 4Vep slam-door stock which came to the end of their lives and they did not meet modern health and safety requirements. Built in the early 2000s, the units had a troubled introduction; being fully air-conditioned, their higher power consumption compared to the slam-door Mark 1 stock that they replaced led to major upgrades being required to the 750 V DC third-rail power supply used in the former Southern region.[1] The collapse of Railtrack following the Hatfield accident further delayed this upgrade work, and the new stock did not enter squadron service until 2003.

Class 377s are fitted with external CCTV. There is an open area for wheelchairs or prams, and both intermediate coaches have toilets. Bodyside power doors are electrically operated, a move away from the air powered systems of previous generation EMUs. Dual-voltage units are fitted with a Brecknell Willis high-speed pantograph, incorporating a pair of aerofoils on the pan knuckle to steady the pan head against the OLE contact wire.[2] The configuration of a 5-car Class 377 unit is:

  • DMOC(A) – 2 motors on inner bogie, sander, auxiliary converter module
  • MOSL – 2 motors on inner bogie, standard toilet (not found on 377/3s)
  • PTSOL – pantograph, transformer, compressor, universal access toilet
  • MOS – 2 motors on inner bogie, standard class interior (only found on Class 377/6 and 377/7 units)
  • DMOS(B) – 2 motors on inner bogie, sander, auxiliary converter module

In 4-car units, the driving cars are composite, with the first-class saloon between the driving cab and the first set of passenger doors. 4-car units also do not contain the MOS coach.[citation needed]


The Class 377 uses Dellner[3] couplers instead of the Tightlock type originally used on Southern's Class 375s. Southern's 375s were all converted to Class 377/3s – these reclassified units can still be identified by their 3-car formation. Note that Southeastern's 375s (sub-classes 375/3, 375/6, and 375/7) were also converted to Dellner couplers, but not reclassified; its 375/8 and 375/9 units were fitted with Dellner couplers as built.[4]

Traction current supply

All units can receive power via third-rail pick-up which provides 750 V DC. There are eight pick-up shoes per unit (twice the number of previous generation 4-car Electric multiple units), and this enables them to ride smoothly over most third-rail gaps. The units in the 377/2, 377/5 and 377/7 sub-classes are dual-voltage, and are fitted with a pantograph to pick up 25 kV AC from overhead lines. On these units the shoe mechanism is air-operated so that when powered down, or working on AC overhead lines, they are raised out of the way. This is used on trains from Milton Keynes to East Croydon which use part of the West Coast Main Line between Milton Keynes and Willesden Junction, and then the West London Line towards Clapham Junction. These trains change to third-rail DC supply on a dual-voltage section of the West London line north of Shepherd's Bush.[5] Since March 2009, dual-voltage Class 377 units have also been operating some Thameslink Bedford to Brighton, Rochester and Ashford services. (See below).

Among the remaining units, the trailer coach in each unit has a recess in its roof where a pantograph could be fitted, to allow for future conversion to overhead AC power.[citation needed]

Additional units and the Thameslink Programme

In April 2007, as part of the Route Utilisation Strategy for the Brighton Main Line, it was announced that Southern would procure an additional 48 Class 377 carriages to replace an identical number of Class 319 carriages (12 4-car units) due to be transferred to First Capital Connect.[6] Eleven further dual-voltage units were then added to the order, making a total of 23. They were ordered from Bombardier in March 2008 and were delivered in First's corporate colour scheme but with Southern spec interior (green seats).[7] The units were commissioned at Southern's Selhurst depot in Croydon before being transferred to First Capital Connect's Bedford Cauldwell depot. The first of these, unit 377501, was delivered to Cauldwell depot on 27 February 2009 after making its first appearance through the Thameslink Central London core. The 377/5s operate mainly on Bedford to Brighton services but in the peaks form part of FCC's and Southeastern's new joint service to places such as Rochester and Ashford. Once FCC's new passenger vehicles come into service, the 377/5 fleet will be returned to Southern.

Delays in the construction of the Class 377/5s for First Capital Connect saw the temporary transfer of eight of Southern's Class 377/2s to FCC to enable them to implement the planned timetable changes on 22 March 2009; the loss of these units until September 2009 was covered by the temporary cascade of a number of Class 350/1s to Southern from London Midland, which operated services between East Croydon and Milton Keynes.[8]

In September 2011, it was announced that Southern had begun the procurement of 130 vehicles, due to delays in the procurement of new Thameslink rolling stock that would prevent transfer of the 377/5s in time for the December 2013 timetable change.[9] The contract was awarded to Bombardier in December 2011.[10][11] The additional eight five-car units (from an option in the contract for 40 additional vehicles) are dual-voltage and known as Class 377/7.[12]

In December 2011, three Class 377/2 units were transferred from Southern to First Capital Connect (now Thameslink) to allow more 12-car services to be run.[citation needed]

During mid-2013, the first of the new Class 377/6s arrived from Derby for type testing, and since October 2013, these units have been used in passenger service, initially in peak-hour services on the Sutton and Mole Valley lines, Epsom Downs Branch, Tattenham Corner Line and the Caterham Line.[citation needed]

Southern Class 377/1 No. 377122 departing Warnham, with a service bound for Horsham
Southern Class 377/2 No. 377202 at Watford Junction, with a service bound for Brighton
Southern Class 377/4 No. 377447 at Hassocks
The interior of Standard Class aboard a Southern Class 377/4
Southeastern Class 377/5 No. 377504 arriving at London Victoria
Southern Class 377/6 No. 377604 about to depart at London Victoria platform 9 with a Sutton service

Southeastern have received 25 Class 377 units in coming years according to Department for Transport documents published in September 2013, relating to the new combined Thameslink, Southern and Great Northern Franchise.[13]

Current operations


  • Mainline and Redhill Routes: London to Brighton, Horsham, Reigate, Tonbridge, Eastbourne, Ore, Portsmouth, Southampton, Littlehampton and Bognor Regis
  • East Coastway: Brighton to Eastbourne, Hastings, Ore and selected workings along the Seaford branch line
  • West Coastway: Brighton to Portsmouth, Littlehampton, Bognor Regis and Southampton (selected workings)
  • West London Route: East Croydon to Milton Keynes Central
  • Oxted Line: London to East Grinstead
  • Outer Suburban services: Central London to Tattenham Corner, Horsham, Dorking, Guildford (selected workings)
  • Inner Suburban services: Central London to Caterham, Sutton, Epsom, Epsom Downs, West Croydon, Beckenham Junction via Crystal Palace (selected workings)


Since December 2016, Southeastern has had 8 units (377501-377508) transferred from Govia Thameslink Railway. In September 2017, these were joined by an additional 17 units (377509-523 & 377163/164).[14]

Southeastern operates Class 377s on the following routes:

  • Maidstone East Line: London Victoria/Blackfriars to Ashford International/Canterbury West via Maidstone East
  • Chatham Main Line: London Victoria/Cannon Street to Ramsgate (selected workings)

Aborted Proposals

Great Northern

In 2016, 19 of the 23 Class 377/5 units were planned to be transferred for use on non-stop London-Cambridge services. However, the 29 former Thameslink Class 387/1s were transferred instead.[15] The Class 377/5s were later transferred to Southeastern as part of their requirement for additional capacity.

Fleet details

Class Operator No. Built Year Built Cars per Unit Unit nos. Notes
Class 377/1 Southern 62 2002–2003 4 377101-162 All 3rd rail routes. 377163/4 transferred to Southeastern in October 2017.[citation needed]
Southeastern 2 377163-164
Class 377/2 Southern 15 2003–2004 4 377201-215 Dual-voltage units.
These are used on the East Croydon – Milton Keynes Central route as well as Metro routes in South London and occasionally main line workings to the South Coast.
Class 377/3 Southern 29 2001–2002 3 377301-328, 377342 3-car units converted from Class 375 Nos. 375311-338 by having their Tightlock couplers replaced by Dellners.
Originally used on Coastway services but have now moved to London suburban services, being partly replaced by Class 313s. One unit converted from a Class 377/4 after fire damage.[16]
Class 377/4 Southern 74 2004–2005 4 377401-441, 377443-475 All 3rd rail routes. One unit converted to Class 377/3 after fire damage.
Class 377/5 Southeastern 23 2008–2009 4 377501-523 Dual-voltage units.
All units were transferred from Thameslink to Southeastern during 2016-17 to bolster their existing Class 375 fleet.
Class 377/6 Southern 26 2012–2013 5 377601-626[12] All 3rd rail five and ten-car routes.
Class 377/7 Southern 8 2014 5 377701-708[12] Additional 8 dual-voltage five-car units used on the East Croydon – Milton Keynes Central services in addition to sharing duties with the 377/6s.[17] The 40 vehicles were built in 5-car formation with dual voltage configuration, costing circa £60 million in total, and they were delivered during 2014 for service entry in December of that year.
Southern Livery
First Capital Connect / Thameslink Interim Livery
Southeastern Livery

Accidents and incidents

On 28 November 2016, a fire broke out in the MOSL car of a Southern Class 377 (unit 377442) at Eastbourne station, causing damage to the ceiling and interior. The cause was later identified to be faulty wiring within a hand dryer located in the toilet.[18]


  1. ^ Ford, Roger (May 2003). "SR power upgrade agreements signed". Modern Railways. London. Archived from the original on 4 June 2011. 
  2. ^ First Capital Connect: Class 377 Drivers' Guide p.91 "The pantograph" 2009.
  3. ^ "Dellner Couplers AB — Automatic and Semi-Permanent Couplers". Retrieved 10 October 2014. 
  4. ^ "Southern Electric Fleet Review Summer 2004". Southern Electric Group. 21 April 2006. Archived from the original on 23 February 2013. 
  5. ^ Jacobs, G. (ed) (2008). Railway Track Diagrams 5: Southern and TfL (3rd edition). Bradford-on-Avon: Quail. p. 1R.
  6. ^ "More trains arriving on busy rail routes". Department for Transport. 4 April 2007. Archived from the original on 5 July 2007. 
  7. ^ "Flickr". 
  8. ^ "All Aboard for the latest game of musical trains on the National Network" (PDF). Railway Herald (169). Scunthorpe. p. 4. 
  9. ^ "Could Southern be the lifeline for Bombardier?" (PDF). Railway Herald (284). Scunthorpe. p. 3. [permanent dead link]
  10. ^ "Boost for Derby as Bombardier wins Southern order". Railnews. 28 December 2011. Retrieved 9 January 2012. 
  11. ^ "DfT acts to ease Thameslink trains logjam". Railnews. 16 November 2012. Retrieved 16 November 2012. 
  12. ^ a b c Today's Railways. March 2013. Issue 135. Page 31. The article states that the additional 8 units were initially 377624-634 but have been reclassified due to the dual-voltage option being taken up.
  13. ^ "Thameslink, Southern and Great Northern Franchise: Invitation to Tender" (PDF). London: Department for Transport. September 2013. p. 75. Retrieved 9 October 2013. 
  14. ^ "Coming to a station near you: 68 extra train carriages on busiest Southeastern routes". Southeastern. Retrieved 18 September 2017. 
  15. ^ "Trio of GTR Class 387/1s readied for move to Great Northern duties". PressReader. Retrieved 4 August 2016. 
  16. ^ "Class 377 Reformation - 377 442 becomes 377 342". RailUK Forums. Retrieved 2017-12-20. 
  17. ^ "Procurement of New Rolling Stock" (Press release). Southern. 15 November 2012. Archived from the original on 29 March 2013. 
  18. ^ "Hand dryer caused Eastbourne train fire". www.eastbourneherald.co.uk. Retrieved 4 June 2017. 

External links