In the design process of electric motors and generators the power losses of stator cores are calculated based on the material supplier’s data from standard magnetic measurements performed under sinusoidal magnetization and with no-external stress exerted on the tested samples. This type of data is insufficient for accurate prediction of machine performance as it does not include the additional loss in the real motor operating conditions from the non-sinusoidal excitation nor the detrimental influence of mechanical and thermal stresses during production of the motor components, such as stator and rotor cores. Furthermore, in the manufacturing of electrical machines a considerable attention is given to the measurements of mechanical dimensions of magnetic cores, whereas verification of their magnetic properties is typically neglected. This in return, leads to inconsistent efficiency of assembled machines as the differences between the actual and initial magnetic properties of the materials and components are significant. In this presentation the experimental data obtained with Brockhaus measurement systems which emphasized the requirement for advanced characterization of stator cores at various design and production stages will be discussed.