Abstract: By combining the calculation method of thermal resistance for the insulation layer from the current rating calculation method of bare overhead conductors with the traditional cable current rating calculation method, a transcendental equation for calculating the surface temperature of overhead insulated cables was derived. The surface temperature value was obtained by programming in MATHCAD and applying the Newton-Raphson iteration method. Subsequently, the current rating of the overhead insulated cable was determined based on the traditional cable current rating calculation principle (heat flow multiplied by thermal resistance equals temperature difference). The calculated results were compared with the actual measured current rating of the overhead insulated cable, validating the feasibility of the new method.