We found COULOMB 3D an ideal tool to calculate the electric fields on big open structures like overhead lines. Due to the nature of the boundary element method it allows the calculation of big arrangements consisting of two towers and 6 phases. The mesh at the specific point of interest can be refined for every calculation providing a detailed electric field plot of a composite insulator close to the end fitting (so called “triple point”). We also appreciated the excellent support of INTEGRATED’s technical support reps helping us to refine and optimize the model. At the end we achieved a calculation time of only 15 minutes, while it was still a couple of hours initially.