The network topology reduction is based on an exact mathematical tool. The principle is a reduction of the problem matrix to a few lines and columns. The original reduction method developed in this study is an extension of this technique implemented to transient heat diffusion problems. The finite volume model is hence reduced to a few chosen nodes and a new type of element appears in the associated network, the compensation capacitance. This element, discussed in (Lagonotte et al., 2001), links every node of the model and improves the dynamic behaviour of the model. Two steps of optimisation, concerning the choice of the nodes and the value of the compensation capacitances, are discussed. The method is implemented to the thermal model of an industrial object, a 5.5 kW squirrel cage induction machine.