This clause provides requirements for the selection and erection of low-voltage and extra-low voltage generating sets intended to supply, either continuously or occasionally, all or part of the installation. Requirements are also included for installations with the following supply arrangements: – supply to an installation which is not connected to a system for distribution of electricity to the public; – supply to an installation as an alternative to a system for distribution of electricity to the public; – supply to an installation in parallel with a system for distribution of electricity to the public supply; – appropriate combinations of the above. This part does not apply to self-contained items of extra-low voltage electrical equipment which incorporate both the source of energy and the energy-using load and for which a specific product standard exists that includes the requirements for electrical safety. NOTE – Requirements of the electricity distributor should be ascertained before a generating set is installed in an installation that is connected to a system for distribution of electricity to the public.