a)switch on the storage system with AC voltage respectively less than 85% and greater than 110% of the nominal value Vn (while the frequency must be between 49.90 Hz and 50.10 Hz), and check that the unit prevents the parallel with the grid – no power supply/consumption according to network analyser reading.b)After at least 30 s from the time of start of the test referred to in point a), check the persistence of the state "open", i.e. absence of output power supply / consumption. At this point bring the voltage within the limits 85 % Vn < V