A plant (1;1b) for powder coating of electrically non-conductive brake pads assembled onto an iron metal support, comprising a pre-treating station (3;3b), in which the electrically non-conductive brake pads are made temporarily electrically conductive, a coating station for electrostatic applying painting powders, a station for melting and polymerizing the painting powders, preferably defined by a tunnel shaped baking oven, and at least one conveyor device adapted to make the electrically non-conductive brake pads assembled onto an iron metal support to be painted move along said stations (3;3b,4,6); wherein the pre-treating station (3;3b) comprises means for making water to be retained on at least one surface to be painted of said electrically non-conductive brake pads and, preferably, on each said entire electrically non-conductive brake pad, to such an extent to produce a measurable increase of weight in the electrically non-conductive brake pads, which makes such brake pads electrically conductive; said painting powder melting and polymerizing station being further configured to eliminate by evaporation at least part of the water previously retained on the electrically non-conductive brake pads; characterized in that, in combination: i)- the pre-treating station (3;3b) comprises a source of low mineral content water, having a specific conductivity comprised between 1 and 5,000 μS/cm, and preferably between 10 and 700 μS/cm, measured at 20°C; ii)- the pre-treating station further comprising: a motorized rolling rack having powered rollers on which the electrically non-conductive brake pads transit tidily; a plurality of nozzles for supplying high pressure jets of said low mineral content water towards the electrically non-conductive brake pads, said nozzles being adapted to create a mist all-around said electrically non-conductive brake pads; at least one feeding pump for said nozzles; and a suction hood (17;17b) arranged facing said nozzles; iii)- the said nozzles being arranged underneath said motorized roller rack at a predetermined vertical gap from the powered roller rack, so that iv)- an empty space is delimited between the rack and said nozzles; and v)- said nozzles address said jets of said low mineral content water onto the electrically non-conductive brake pads from the bottom upwards while the brake pads move upon the powered rolls, vi)- said suction hood (17;17b) being arranged over the motorized roller rack. i)- the pre-treating station (3;3b) comprises a source of low mineral content water, having a specific conductivity comprised between 1 and 5,000 μS/cm, and preferably between 10 and 700 μS/cm, measured at 20°C; ii)- the pre-treating station further comprising: a motorized rolling rack having powered rollers on which the electrically non-conductive brake pads transit tidily; a plurality of nozzles for supplying high pressure jets of said low mineral content water towards the electrically non-conductive brake pads, said nozzles being adapted to create a mist all-around said electrically non-conductive brake pads; at least one feeding pump for said nozzles; and a suction hood (17;17b) arranged facing said nozzles; iii)- the said nozzles being arranged underneath said motorized roller rack at a predetermined vertical gap from the powered roller rack, so that iv)- an empty space is delimited between the rack and said nozzles; and v)- said nozzles address said jets of said low mineral content water onto the electrically non-conductive brake pads from the bottom upwards while the brake pads move upon the powered rolls, vi)- said suction hood (17;17b) being arranged over the motorized roller rack.