The BCI (Bulk Current Injection) test in electromagnetic compatibility is a reference scenario widely used in industry for the conducted immunity evaluation of electronic equipment. Quantifying the influence of all geometrical parameters is a key challenge. This work shows that a fast sensitivity analysis can be performed with the use of a small number of sampling data thanks to metamodelling used to compute Sobol indices. The interest of the approach is demonstrated through a susceptibility analysis involving a realistic multi-conductors line under probe.