The objective of this paper is to validate the electric field measurement technique for the diagnosis of uon-ceramic insulators (NCI). To validate this technique, fifteen NCI were aged in a salt fog chamber by applying uon-staudard methods. Before ageing the NCI, the electric field distribution aloug each insulator was measured (sound field curve). When an insulator flashed over during the ageing test, the insulator was removed from the salt fog chamber and its electric field distribution was again measured (aged field curve). AU the insulators that flashed over had visible defects and showed an electric field distribution different to that initially Obtained. The comparison between the sound field and aged field curves for these insulators validated the location of the defects along the insulator. On the other hand, the electric field distribution measured on insulators which had no visible defects was similar to that initially obtained. This means that for these cases the flashover was only caused by the pollution phenomenon, and not by any defect Furthermore, the electric field distribution measurements on all the insulators at the middle and at the end of the ageing test were performed, in order to mainly determine if some internal defect in the insulators, without visible defects, had occurred