This paper presents a lumped parameter approach for three-dimensional (3D) thermal modelling based upon the use of general 3D elements which are formulated to accurately cater for internal heat generation. Commonly used thermal networks tend not to account for an internal heat generation that is essential for accurate temperature predictions. In contrast, the general element proposed in this paper includes the internal heat generation as well as a material thermal anisotropy. To validate the technique, thermal models of an inductor using the equivalent circuit method based around a general cuboidal element and a full 3D finite element analysis was constructed and analyzed. The calculated results from the cuboidal element method show good agreement with the FEM predictions.