An air filtering system for an electrical enclosure including at least one filtering element arranged to filter an air flow injected into the inlet of the enclosure by a fan device, the system also including several independent filtering cells Ci, with i ranging from 1 to n and n greater than or equal to 3, each filtering cell Ci having a variable filtering capacity, each filtering cell Ci, with i greater than or equal to 2, is rendered active to filter a part of the air flow when the sum of the filtering capacities of the cells, ranging from C1 to Ci−1, drops below a specific threshold.