Abstract—To provide the accurate thermal rating of overhead power lines is required to consider the conductor temperature depending on a variety of weather factors. New types of conductors, such as overhead insulation-covered conductors are widely used in electrical networks. Well-known IEEE 738 and CIGRE standards calculate the bare overhead conductors only and are not applicable for thermal rating of overhead insulation-covered conductors. Numerical methods are able to calculate the insulated conductors, but have many drawbacks, such as the difficulty of modeling and low computation speed. The authors propose an analytical mathematical model to determine the thermal rating both overhead insulation-covered and bare conductors. Results of temperature calculation and active power losses calculation for overhead insulation-covered and bare conductors with the same cross section at selected weather conditions and changes in load current have been presented. Neglect of insulation can lead to errors in calculating of temperature up to 30%.