Electrical enclosure intended to house electrical devices and having an air inlet, an air outlet, a fan device arranged to favour the injection of air through the air inlet of the enclosure, and a filtering system positioned at the air inlet, upstream from the fan device relative to the direction of air injection into the enclosure, characterized in that the filtering system comprises: several independent filtering cells Ci, with i ranging from 1 to n, and with n greater than or equal to 2, each filtering cell Ci having a filtering capacity that is variable over time, the cell or cells Ci with i greater than or equal to 2 being configured to be individually and successively moved from a deactivated state to an activated state to filter a part of the air flow when the sum of the filtering capacities of the filtering cells which have already been activated drops below a predetermined threshold, a main filtering cell C1 which is initially active and through which passes the entire air flow created by the fan device when all the other filtering cells are still inactive, each filtering cell Ci with i greater than or equal to 2 having a valve 201 which is capable of moving between a closed position when the filtering cell is inactive and no part of the air flow passes through it, and an open position when the filtering cell is active and a part of the air flow passes through it, the filtering system further comprising: means for measuring the filtering capacity of the cells, control means capable of causing the activation of an additional filtering cell when the aforementioned sum of the filtering capacities becomes less than said specific threshold, each filtering cell Ci, with i greater than or equal to 2, being rendered active by opening of the aforementioned valve, to filter a part of the air flow, and in that Q being the entire air flow created by the fan device when all the other filtering cells are still inactive, the aforementioned specific threshold is Q/2, and in that after the control, it is Q/2 that flows through the newly activated filter. several independent filtering cells Ci, with i ranging from 1 to n, and with n greater than or equal to 2, each filtering cell Ci having a filtering capacity that is variable over time, the cell or cells Ci with i greater than or equal to 2 being configured to be individually and successively moved from a deactivated state to an activated state to filter a part of the air flow when the sum of the filtering capacities of the filtering cells which have already been activated drops below a predetermined threshold, a main filtering cell C1 which is initially active and through which passes the entire air flow created by the fan device when all the other filtering cells are still inactive, each filtering cell Ci with i greater than or equal to 2 having a valve 201 which is capable of moving between a closed position when the filtering cell is inactive and no part of the air flow passes through it, and an open position when the filtering cell is active and a part of the air flow passes through it, the filtering system further comprising: means for measuring the filtering capacity of the cells, control means capable of causing the activation of an additional filtering cell when the aforementioned sum of the filtering capacities becomes less than said specific threshold, each filtering cell Ci, with i greater than or equal to 2, being rendered active by opening of the aforementioned valve, to filter a part of the air flow, and in that Q being the entire air flow created by the fan device when all the other filtering cells are still inactive, the aforementioned specific threshold is Q/2, and in that after the control, it is Q/2 that flows through the newly activated filter. means for measuring the filtering capacity of the cells, control means capable of causing the activation of an additional filtering cell when the aforementioned sum of the filtering capacities becomes less than said specific threshold, each filtering cell Ci, with i greater than or equal to 2, being rendered active by opening of the aforementioned valve, to filter a part of the air flow, and in that Q being the entire air flow created by the fan device when all the other filtering cells are still inactive, the aforementioned specific threshold is Q/2, and in that after the control, it is Q/2 that flows through the newly activated filter.