The Electrical Multiple Unit

The Multiple refers to more than one driving motor.

Non high speed EMUs

Above: A 1958 EMU capable of 90 mph, 144km/h

These are similar to urban underground (subway) trains. The principal is that they pick up electricity, and connected to the axles of some of the passenger cars are electric motors, with the appropriate transformers sitting underneath the carriage. On these trains are most widely used for stopping services. However most of them are faster than their diesel counter parts, the majority can go up to 90 mph, and some as fast as 100 mph, for further details see the EMU list. They were developed first in Kent where electrification was first introduced into the UK. The non-high speed type range from coming as a 2 car set to a 5 car set, although in operation many sets may be coupled together to provide the capacity required.

Above: Built in 1981 its a fast EMU with a top speed of 100mph, 160km/h

The acceleration of EMUs is extremely good, often providing performance you would only expect from a car. This is because they are very light and having many traction motors helps. This is why they are often used for frequently stopping services, as it only takes a few seconds to get up to speed, keeping the average speed up.Modern EMU trains have been fitted with regeneration equipment, so that when braking to come to a stop they generate electricity which can be fed back into the system, reducing their overall power requirements. This gives big savings. The reason why recent classes such as the 455 have such low speeds (75mph) is that they are only meant for short-haul suburban services, leaving the faster EMUs to do express services to towns outside of cities.

High Speed Trains

Often high speed trains are considered to be EMUs, because they have more than one engine, as they have an engine at both ends, or several motorised carriages. TGVs are classed as being EMUs. The Eurostar is in fact the longest EMU in the world, as it is a 20 car set, and over 400 meters (1/4 of a mile) long.

Above: The modern 456 class built in 1991. Top speed only 75mph, 120km/h

High Speed EMUs are generally different from non high speed EMUs in that they have a recognisable engine compartments, and usually are in a streamlined shape. Acceleration of these is not so good, usually because they are more heavy and because the motors have been designed for cruising rather than stopping and starting.