Class 377 Electrostar

The "Electrostar" Class 377 is the largest fleet of EMUs built since rail privatisation. It was built to replace "slam door" stock, most notably 4-CIG and 4-VEP EMUs on commuter services around London and rural services in the South East [1].

The Class 377 usually operates off the former Southern Railway/Region 750v DC 3rd rail system though some have pantographs and can operate 25kV AC overhead lines for cross-London services and can venture up as far as Milton Keynes Central and St. Albans. Some Class 377s have been converted from the similar Class 375 as detailed below.

Number built: 211 sets (plus 28 sets converted from Class 375)
Built: 2002-14
Builder: Bombardier Derby
Motor: 6 or 4 Bombardier traction motors
Power: 2, 120 hp (1, 500 kW) or 1, 341 hp (1, 000 kW)
Formation: Driving Motor Composite Open (DMCO)+Motor Second Open (MSO)+
Trailer Second Open (TSO)+DMCO

They are in service with Southern and Southeastern, having also been used by Thameslink. The fleet is split into a number of sub-classes with various detail changes and in a variety of train lengths as detailed below.

Sub-class Details
377/1 Original, third-rail DC 4-car operated by Southern
377/2 Dual voltage 4-car operated by Southern and Thameslink
377/3 Third rail DC 3-car units converted from Class 375s operated by Southern
377/4 Third rail DC 4-car operated by Southern
377/5 Dual voltage 4-car operated by Thameslink
377/6 Third rail DC 5-car operated by Southern
377/7 Dual voltage 5-car operated by Southern

As well as the Class 377 there are also similar EMUs in the Electrostar family including the Class 375 and 387.
Southern 377 612 at London Bridge

Southern 377 701 at West Brompton

Thameslink 377 511 at Bedford

Southern 377 622 at Clapham Junction

Southern 377 705 at Hemel Hempstead

Southern 377 161 at Portsmouth Harbour

[1] Colin J. Marsden, DMU and EMU Recognition Guide (Ian Allan, 2013) p. 288