The present report deals with some EMC problems relative to interference involving earthing installations. In particular, 50/spl divide/60 Hz conductive interferences are examined, in order to evaluate how they can cause malfunctions of those electronic systems which are very susceptible to external influences. To this purpose, two different configurations of earthing system are analysed, chosen among those more frequently used. The computation of the current derived from each single part of the earthing system (in normal conditions and in short-circuit conditions) and the corresponding elaboration of the equivalent electric circuit allow estimation of the magnitude of such interferences as voltages between different points of the earthing system. This evaluation, account being taken of the electronic systems earthing modality, leads to a significant determination of the most critical situations of possible electronic malfunctions related to the connection to the earthing system.
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