This technical specification sets immunity requirements for apparatus intended for use by Electricity Utilities in the generation, transmission and distribution of electricity and related telecommunication systems. The locations covered are the power stations and the substations where apparatus of Electricity Utilities are installed. Immunity requirements are given for the frequency range 0 Hz to 400 GHz, but only in respect of electromagnetic phenomena for which detailed test procedures, test instrumentation and test set-up are given in existing IEC basic standards. The immunity requirements are suitable for satisfying the particular needs related to the functions and tasks of equipment and systems, for which reliable operation is required under actual electromagnetic conditions; in this respect, this technical specification establishes performance criteria for the different functional requirements.