Prime mover (locomotive)

In a diesel-mechanical locomotive, the prime mover is the diesel engine that is mechanically coupled to the driving wheels (drivers).

In a diesel-hydraulic locomotive, the prime mover is the diesel engine that powers the pumps of one or more torque converters mechanically coupled to the drivers.

In a diesel-electric locomotive, the prime mover is the diesel engine that rotates the main generator responsible for producing electricity to power the traction motors that are geared to the drivers.

In either case, the generator, traction motors and interconnecting apparatus are considered to be the power transmission system and not part of the prime mover.

A wired-electric or battery-electric locomotive has no on-board prime mover, instead relying on an external power station.