British Rail Class 377

British Rail Class 377 Electrostar
A Southern Class 377/1 at Clapham Junction in 2024
The interior of a Southern Class 377/6
In service	May 2003 – present
Manufacturer	Bombardier Transportation
Built at	Derby Litchurch Lane Works
Family name	Electrostar
Replaced	Class 319 Class 421 Class 423 Class 455 Class 456 Class 313
Number built	211 units (excluding 28 375/3 conversions)
Successor	Class 700 (Thameslink)
Formation	377/1/2/4/5: 4 cars per unit (DMOC-MOSL-PTOSL-DMOC) 377/3: 3 cars per unit (DMOC-PTOSL-DMOS) 377/6/7: 5 cars per unit (DMOC-MOSL-PTOSL-MOS(2)-DMOS)
Operator(s)	Southern Southeastern
Specifications
Car length	20.4 m (66 ft 11+1⁄8 in)
Width	2.80 m (9 ft 2+1⁄4 in)
Height	3.78 m (12 ft 4+7⁄8 in)
Maximum speed	100 mph (161 km/h)
Weight	173.6 t (170.9 long tons; 191.4 short tons) (377/1, /2, /4, /5) 133.1 t (131.0 long tons; 146.7 short tons) (377/3 only)
Traction motors	4–8 × 200 kW (270 hp)
Power output	1,200 kW (1,600 hp) (377/1, /2, /4, /5) 800 kW (1,100 hp) (377/3 only) 1,400 kW (1,900 hp) (377/6 and /7)
Electric system(s)	750 V DC 3rd rail 25 kV 50 Hz AC Overhead lines (377/2, 377/5 and 377/7 only)
Current collection method	Contact shoe Brecknell Willis pantograph (377/2, 377/5 and 377/7 only)
Coupling system	Dellner
Multiple working	Within class, Class 378 and Class 379
Track gauge	1,435 mm (4 ft 8 1⁄2 in) standard gauge

The Class 377 Electrostars are electric multiple units built by Bombardier Transportation (previously ADtranz) at their Derby Works, from 2001-2014. The Electrostar family, which also includes Classes 357, 375, 376, 378, 379 and 387 and is the most numerous type of EMU built in the post-privatisation period of Britain's railways.