The knowledge of the inherent common-mode voltage of voltage source inverters and its impact on the mechanical drive train elements is an important issue. With the help of model-based calculations it is possible to identify critical operating points. In addition to the influence of the converter, different operating conditions such as speed and temperature have a main influence on the resulting discharge activity. An extended probability model for the drive train of converter-fed electric motors, including the gearbox components, is developed in this work. The extended model can be used to predict the EDM activity in the motor and the gearbox as well as the influence of different parameters such as converter modulation.