An equivalent circuit of a single conductor line (Sommerfeld wave) is proposed. The circuit is based on physical quantities, such as the electric current and on the power of the traveling wave, while the line voltage is only indirectly obtained. The characteristic impedance and the per-unit-length parameters are calculated in closed form as functions of the complex wave numbers, which must be determined numerically. The circuit parameters are partly confirmed by literature results, and they differ only where the literature results have no physical meaning (e.g. negative conductance). Furthermore, circuit simulation solutions are used to determine the per-unit-length attenuation, and the results are confirmed by the well known analytical solution. The idea can be extended to other type of single conductor lines, having a more complex cross-sectional profile and inhomogeneous media.