This work presents the basis of a new approach for fault diagnosis in Electrical Distribution Systems (EDS). This approach aims to classify different types of faults by means of the factor named as Negative Sequence Factor (F2). This factor is calculated from post-fault negative sequence and pre-fault positive sequence currents using Thévenin equivalents. Series, shunt and simultaneous faults with cable either on the source or on the load side are considered. A simple test case was used to show the effectiveness of the proposed methodology.