This part of IEC62257 specifies the general requirements for the selection, sizing, erection and operation of generator sets in decentralized rural electrification systems. It applies to all low voltage combustion engine electricity generator sets energized by renewable energy such as biomass gasifier or biogas, or fossil fuel such as gasoline or diesel fuel, and designed for supplying electrical power to isolated sites used in systems as described in IECTS62257-2. This document is not an exhaustive resource for the design, installation, operation or maintenance of generator sets, but is more focused on recommendations to provide strategies on selection and criteria which may affect the use of such generation systems in a rural electrification project. Four cases of micropower plant will be considered as illustrated by Figure1 to power a collective electrification system (microgrid) or an individual electrification system. the micropower plant is composed of one generator set; the micropower plant is composed of multiple generator sets, which may have a single energy source or multiple energy sources; the micropower plant which is a hybrid energy system between one generator set and a Power Conditioning Sub-system (PCS) which is powered by other energy source including renewable energy source or energy storage; the micropower plant which is a hybrid energy system between multiple generator sets and multiple Power Conditioning Sub-systems (PCSs) which are powered by other energy sources including renewable energy sources or energy storage systems.Figure1 General functional configuration of micropower plant in micropower system The aim of this document is to provide users with the appropriate guide to select generator sets for using in micropower plant with different configurations and levels of reliability and safety of the equipment during its estimated service lifespan. It describes the minimum requirement of generator set functionality and safety requirements and does not claim to be an exhaustive instruction manual or design specification. Compliance with this document does not exempt any person, organization or corporation from the responsibility to comply with all other relevant requirements including what is indicated in maker user manuals and local electrical regulations. This document gives recommendations for the following types of generator sets: single phase; three phase; LV range up to 500V – 50/60Hz (see IECTS62257-9-2).