The packaged combination of a diesel engine, a generator and various ancillary devices (such as base, canopy, sound attenuation, control systems, circuit breakers, jacket water heaters and starting system) is referred to as a generating set or a diesel generator set for short.

    Set sizes range from 8 to 30 kW (also 8 to 30 kVA single phase) for homes, small shops & offices with the larger industrial generators from 8kW (11 kVA) up to 2,000 kW (2500 kVA three phase) used for large office complexes, factories. A 2,000 kW set can be housed in a 40 ft ISO container with fuel tank, controls, power distribution equipment and all other equipment needed to operate as a standalong power station or as a standby backup to grid power. These units, referred to as power modules are gensets on large triple axle trailers weighing 85,000 lbs or more. Combination of these modules are used for small power stations and these may use from one to 20 units per power section and these sections can be combined to involve 100's of power modules. In these larger sizes the power module (engine and generator) are brought to site on trailers separately and are connected together with large cables and a control cable to form a complete sychronized power plant.

    Diesel generators, sometimes as small as 200 kW (250 kVA) are widely used not only for emergency power, but also many have a secondary function of feeding power to utility grids either during peak periods, or periods when there is a shortage of large power generators.

    Ships often also employ diesel generators, sometimes not only to provide auxiliary power for lights, fans, and winches, etc. but also indirectly for main propulsion. With electric propulsion the generators can be placed in a convenient position, to allow more cargo to be carried. Electric drives for ships were developed prior to WW I. Electric drives were specified in many warships built during WW II because manufacturing capacity for large reduction gears was in short supply, compared to capacity for manufacture of electrical equipment.[1] Such a diesel-electric arrangement is also used in some very large land vehicles.

    Generating sets are selected based on the load they are intended to supply power for, taking into account the type of load, i.e. emergency or for continuous power and the size of the load, and the size of any motors to be started which is normally the critical parameter. Factors such as maximum power, prime power rating and load combinations must be considered when selecting generator sizes. Environmental conditions such as altitude, temperature and emissions regulations must be takend into account as well. Often there is a least one conplete spare generator in a set of generators to allow for main taninance and to have a spare unit in the event that a breakdown occurs.