Earlier results for guided electromagnetic waves on buried cables are recast in terms of internal and external impedances. Then it is possible to deduce the excited cable current in terms of the applied axial electric field. Explicit numerical data are presented for low frequencies when the outer cable diameter is small compared with the electrical skin depth of the surrounding earth. Of particular importance is the remarkable fact that the deduced attenuation rate and phase velocity of the dominant transmission mode depends only slightly on the burial depth of the cable.