System of installation of a plurality of droppers of an overhead contact system section, which comprises at least a contact wire and at least a messenger wire hung between two successive supporting poles (31, 32) delimiting the ends of said overhead contact system section, the system comprising: - a means of measuring a distance (d) between said two successive supporting poles; - a computer programmed to output a layout plan indicating a position and a length for each dropper of the plurality of droppers to be installed based on inputted data, that comprises at least the distance (d) measured by the means of measuring a distance; - a machine for preparing each dropper to be installed at the length thereof indicated in the layout plan output by the computer; - a first platform capable of moving along the overhead contact system section, the first platform being equipped with a position unit for determining the actual position of the first platform and a marking device to set a mark on the at least one contact wire, the marking device being capable of setting a mark on the at least one contact wire each time the position determined by the position unit corresponds to a position of a dropper of the plurality of droppers as indicated in the layout plan; and, - a second platform capable of moving along the overhead contact system section and provided with an aerial device loaded with the droppers that have been prepared, the second platform being thus suitable for a person to fix the droppers in place, the marking device comprising a paint container, an actuated valve and a nozzle situated at the extremity of a mast so as to be in the vicinity of the contact wire, so that, each time the valve is actuated, a spray of paint is applied through the nozzle onto the contact line, the marking device being actuated by the positioning unit each time the current position (p) of the first platform is equal to the position (pi) of a dropper as indicated by the layout plan, which have been loaded into the positioning unit, and the first platform being also equipped with a dedicated system that is able to apply a final tension to the contact wire, the tension being applied on the contact wire during the movement of the first platform, the marks being then drawn on the contact wire correctly stretched. - a means of measuring a distance (d) between said two successive supporting poles; - a computer programmed to output a layout plan indicating a position and a length for each dropper of the plurality of droppers to be installed based on inputted data, that comprises at least the distance (d) measured by the means of measuring a distance; - a machine for preparing each dropper to be installed at the length thereof indicated in the layout plan output by the computer; - a first platform capable of moving along the overhead contact system section, the first platform being equipped with a position unit for determining the actual position of the first platform and a marking device to set a mark on the at least one contact wire, the marking device being capable of setting a mark on the at least one contact wire each time the position determined by the position unit corresponds to a position of a dropper of the plurality of droppers as indicated in the layout plan; and, - a second platform capable of moving along the overhead contact system section and provided with an aerial device loaded with the droppers that have been prepared, the second platform being thus suitable for a person to fix the droppers in place, the marking device comprising a paint container, an actuated valve and a nozzle situated at the extremity of a mast so as to be in the vicinity of the contact wire, so that, each time the valve is actuated, a spray of paint is applied through the nozzle onto the contact line, the marking device being actuated by the positioning unit each time the current position (p) of the first platform is equal to the position (pi) of a dropper as indicated by the layout plan, which have been loaded into the positioning unit, and the first platform being also equipped with a dedicated system that is able to apply a final tension to the contact wire, the tension being applied on the contact wire during the movement of the first platform, the marks being then drawn on the contact wire correctly stretched.