Abstract : This study is about modelling the electric machines by reluctance networks for diagnosis purposes. A method of modelling electric machines is established, trying to make the model as simple as possible, and using only machine geometry data for the model definition. This method was applied to the synchronous and to the asynchronous machine. The synchronous machine model is used to simulate different machine faults: static and dynamic eccentricity, rotor and stator short circuits. The behaviour of different machine variables (shaft voltage, currents between parallel-connected windings, voltage between neutrals) is studied. The model is validated by comparison between simulation results and those obtained by experiments and by finite elements method. It is possible to use the presented model for the fault location. The asynchronous machine model has been tested for the following faults: eccentricities, broken rotor bars, stator short circuits. The diagnosis is performed by stator current spectral analysis. The model is validated through experiments. Faulty machine dynamic behaviour is also studied, by using this model.