In this paper, impact of the causality of frequency-dependent models of soil on the effective area of grounding grids buried in single and two-layer soils is studied. In the analyses, the computationally efficient multi-conductor transmission line method is used. The simulation results show that the causality plays an important role on the effective area so that it can decrease or increase the effective area in comparison with the non-causal model. This reduction or increase depends on the lowfrequency resistivity of dispersive soil and current waveform. The relative error due to non-causality is considerable only for the subsequent stroke current, whereas for the first stroke current, it is low enough to be ignored. In addition, the burial depth effect on the effective area in causal and non-causal-dispersive soils is investigated. With the aim of more accurate design, comprehensively predicting formulae for effective area versus low-frequency resistivity of soil, burial depth and current waveform under causal assumption are proposed. Finally, importance of effective area based on causal and non-causal models on the lightning-induced voltage on the soil surface is investigated.
