ER2 electric trainset

ER2
Electric multiple unit ER2-1290 "Karelia"
Manufacturer	Rīgas Vagonbūves Rūpnīca
Constructed	1962-1984
Number built	850 (modifications not included)
Formation	4, 6, 8, 10, 12 cars
Specifications
Car body construction	steel, aluminium
Car length	19.60 m (64 ft 4 in)
Width	3,480 mm (11 ft 5 in)
Height	5,086 mm (16 ft 8.2 in)
Maximum speed	100 km/h (62 mph) (from January 2008)
Acceleration	0.6 m/s2 (2.0 ft/s2)
Deceleration	0.8 m/s2 (2.6 ft/s2)
Electric system(s)	3 kV DC Catenary
Current collection method	Pantograph
Coupling system	SA3
Track gauge	1,520 mm (4 ft 11 27⁄32 in) Russian gauge

The ER2 electric trainset is a DC electric multiple unit which was in production by the Railroad Machinery Plants of Riga (in consortium with the Electrical Machinery Plants of Riga and the Railroad Machinery Plants of Kalinin) from June 1962 to mid-1984. It was essentially an improvement of the ER1 design, featuring footboards for low platforms, and aprons for high platforms, as well as improved electrical equipment and minor changes to the bodywork (specifically, the engineer's cab, side walls, headstocks, and door mountings). Since the mid-1960s, the ER2 has been the most widely used type of suburban train in the Soviet Union and its successor states.

Electric multiple units were first used in the Soviet Union in 1926 on the Baku-Sabuncu segment of the Baku mainline. These consisted of 2-car or 3-car sections, each of which had 1 power car and 1 or 2 trailer cars (a similar consist to that still used today). The motor cars used 1200 V DC current and had 4 75-kW motors for a total power output of 300 kW. These trainsets were retired in the 1940s.

In August 1929, a second electrified suburban line was opened, from Moscow to the northern suburb of Mytischi. This line operated the S-series electric multiple units (S standing for "Severnye Zheleznye Dorogi", or "Northern Railroad"). These consisted of standard 3-car sections, each section having 1 power car and 2 trailers. The power cars used 1500 V DC current and had a total power of 600 kW (up to 720 kW on later versions). The electrical equipment for these trains was manufactured by Metropolitan Vickers (later license-built by the Dynamo factory in Moscow), and the mechanical equipment was made by the Mytischi Railroad Machinery Plant. After World War II, the entire production was transferred to the Riga Railroad Machinery Plant, which continued producing these trainsets until 1958. The many versions of the S-series trains produced included 1500-V and 3000-V versions, dual-current versions and some versions fitted with dynamic brakes. All of these had one common design flaw: the traction motors were mounted directly on the axles to simplify manufacture, which in turn limited maximum speed to 85 km/h.