In this paper, an approximate modeling approach called simplified multiconductor transmission line model (simplified MTL) is proposed for transient analyses of multiple grounding electrodes. Since this approach is in the frequency domain, the effect of soil dispersion (frequency variation of soil electrical parameters) is easily incorporated. In addition, the soil ionization effect is treated as gradually increasing radius of the electrode. With the use of this approach, predicting formulae for effective length of multiple grounding electrodes considering both ionization and dispersion are proposed for the first time. Finally, combining the extracted formulae with the apparent resistivity in two‐layer soils, effective length in such soils is easily predicted.