Electric motor systems are composed of three subsystems: components required to control electricity to the motor; the motor itself; and the motor-driven mechanical equipment, such as fans, pumps or compressors, that perform useful work. Each of these subsystems serves a distinct purpose.

• The facility power distribution equipment supplies electricity of the appropriate voltage and frequency to the motor and controls, so the control components can serve four basic functions:

(a) starting, directing, and protecting the operation of the motor and driven equipment;
(b) varying the process output;
(c) providing feedback from measured parameters to the control circuit; and
(d) ensuring personnel safety.

• The motor then converts electrical energy to mechanical power and transfers it to the load directly through a coupling or through transmission equipment such as gears or belts.

• Next, the mechanical equipment performs work. In some cases, the work done by this equipment directly satisfies a need (e.g., a milling machine) while in other cases the equipment is part of a more complex system that meets an end-use need such as cooling or heating. These systems usually include a distribution network (e.g., piping or ducting) to transport the working fluid to the process or end-use where the work is accomplished. The end-use and its requirements dictate the other components of the system, which may include accessory equipment such as dryers and filters that condition a fluid stream.

Motor systems may be defined as either a "packaged system" or an "integrated system." A packaged system refers to a fan/blower, air compressor, or process pump system that is packaged and sold as a single unit, containing a motor, drive train, controls, outlet devices, and ancillary components.  For example, a fan is a package consisting of an electric motor and a bladed impeller within a structural housing.  In contrast, an integrated system refers to the entire system boundary, from the energy input to the process itself, including the piping/ducting distribution system, controls, motors, driven-equipment, and downstream process equipment. The amount of energy consumed by the system is defined by the interaction of the components, not just the efficiency of individual components or packages (Energy-Efficient Motor Systems Handbook).