An increasing number of electric vehicles (EVs) will have a significant impact on the electricity grids. For target grid planning, it is essential to identify and quantify this impact in terms of local infrastructure overloads. We study the impact of EV charging loads on Swiss distribution substations under different penetration levels and pricing regimes. Unlike mainly conceptual studies focusing on generic distribution grids, we use real data—driving profiles matched to regional circumstances, Swiss substation capacity and load data in the high-voltage grid together with electricity prices—as the main data inputs. To reflect current regulation and contracting schemes, we apply decentral decision-making instead of central control. The results indicate that under a flat electricity tariff and EV penetration levels around 16% the current substation capacity will be sufficient to cover additional EV charging load. However, beyond penetration levels of 50% an increasing number of substations will be overloaded. More significantly, the introduction of dynamic electricity prices can further increase the risk of substation overloads. These results show that EV charging loads can also cause bottlenecks on substations in the high-voltage grid.