The current uptake of electric vehicles (EVs) results in new challenges for the electricity grid. Due to their relatively high power and potentially synchronized demand, existing local grid capacity might become inadequate in the near future. To provide insight into this development, this work proposes an approach to approximate the outage probability in low-voltage (LV) grids due to EV charging. The introduced model can be used as a tool to understand the impact of uncontrolled EV charging in existing and new LV grids. A case study demonstrates this approach with a grid of 40 households: at 35% EV penetration rate the outage probability is approximately once every 50 days.