The introduction of Plug-in Electric Vehicles (PEV) increases the electricity consumption especially on the distribution grid. The distribution grid planners have to take into account these changes in future investments. In this paper the impact of PEVs on the sizing of medium voltage lines and cables cross section is evaluated. A sensitivity analysis is conducted in order to calculate the parameters' weight. Then Monte Carlo simulations are made to assess the impact of electricity price volatility on sizing. We show that in the case of 2 million PEVs in 2020 in France, reinforcement will account for 5.5% of conductor cost.