## 3 Analysis of Input Parameters and an Overview of the Effective Length Dataset  
Using the previously described methodology, we performed a series of numerical simulations to determine the influence of various input parameters (features) on the effective length of the type-A grounding system. Specifically, we performed a total of 880 simulations, varying three key features: soil resistivity, burial depth of the ground electrode, and the rise time of the lightning current dissipated into the surrounding soil. Please note that the results of simulations are available for download as a public dataset [24]. In the international standard [16], a type-A grounding system is recommended for use in soils with resistivity values up to 3000 \(\Omega\)m, effectively establishing an upper limit for our selected feature set. As for the lower limit of our soil resistivity feature set, reference [25] and several other sources indicate that soils originating from the Cretaceous period exhibit \"unusually low\" resistivity values, with loam and clay reaching as low as 10 \(\Omega\)m. With the lower and upper limits established, other values in our soil resistivity feature set are (more or less) uniformly selected within the defined interval, resulting in a set of 11 soil resistivity values: \(\rho\) = {10, 50, 100, 250, 500, 750, 1000, 1500, 2000, 2500, 3000} \(\Omega\)m. Note that more soil resistivity values were selected in the interval up to 1000 \(\Omega\)m for our feature set, which is consistent with reference [25], where a larger number of soil types are also listed in the mentioned interval. Note that in [25], soil types of resistivity values 1000 \(\Omega\)m and 3000 \(\Omega\)m are characterized as having \"high\" and \"very high\" resistivity, respectively, indicating that soils with these kinds of resistivities are less common, which is consistent with our feature set selection. The second feature we varied in the mentioned simulations that potentially influenced the effective length of the grounding electrode was the electrode burial depth. Similar to the soil resistivity value selection, in this case, we also chose a realistic interval of electrode burial depths, ranging from 0.25 m to 2 m (see for example [26]). This resulted in a set of eight type-A grounding system burial depths: \(d\) = {0.25, 0.5, 0.75, 1.0, 1.25, 1.5, 1.75, 2.0} m.  
The third and final feature we varied in the simulations was the rise time of the lighting current that is dissipated into the surrounding soil via the type-A grounding system. Observing the recent statistical analysis of real lightning strikes in [27] and the rise times prescribed for positive and negative subsequent strokes in the international standard [28], the following set of ten rise time values was selected: \(T_{1}\) = {1.0, 2.0, 3.0, 4.0, 5.0, 6.0, 7.0, 8.0, 9.0, 10.0} \(\mu\)s.  
An excerpt from the dataset [24] containing all combinations of previously described features along with the computed values of the type-A grounding system effective length (of each electrode) is provided in Table 1. A visualization of these data is slightly problematic since the dataset contains three feature columns and one response column, which would correspond to a 4D plot. Although possible, we found that the readers would best benefit if we isolated, for example, all the data for the burial depth of 0.5 m. Note that a 3D surface  
Figure 2: Methodology of obtaining the effective length dataset. plot has been generated in Figure 3 instead of only the data points. This visual interpolation was performed solely to improve the reader's viewing experience. After performing all 880 simulations and determining the effective lengths of each type-A grounding electrode, a preliminary analysis of feature importance was performed using the Minimum Redundancy Maximum Relevance (MRMR) algorithm [29]. As expected, it was determined that not every selected feature has a significant impact on the effective length of the grounding electrode.