Apparatus for the production of an electric conductor provided with at least a layer of coating plastic material. The apparatus comprises: a head for the extrusion of an electric conductor; at least a main extruder having a first supply duct; at least an auxiliary extruder having a second supply duct; and a device for the selection and the diversion of the flows of coating plastic material. The selection and diversion device is provided, in turn, with at least a device for the exclusion of the auxiliary extruder; with a bypass duct between the first duct and the second duct; and with a flow-regulating diverter valve arranged in the intersection point between the first supply duct and a bypass duct connecting the first duct to the second duct.