This article discusses the accuracy of the method recommended by the IEC 60287-1-1 for including skin and proximity effect in the estimation of the ac resistance of two parallel conductors at the supraharmonic range (2-150 kHz). The IEC resistance model is compared against a generalized model in order to visualize and quantify the error incurred when using the standard's simplified formula for typical low-voltage conductors carrying supraharmonic distortion. The study reveals that the cable resistance model used impacts the resonance peak attenuation, leading the IEC formula to show errors as significant as 14%.