A new implementation of the mutually constrained partial differential and integral equation method for the exterior 2-dimensional field problem is described. It is shown, that the method is applicable to exterior problems in an inhomogeneous medium. The inhomogeneity is considered in the finite element procedure and in boundary element method, where an adequate Green's function is applied. The temperature distribution around a three-cable system is then computed as an illustration. The eddy-current losses in the cable sheaths are calculated using the Fredholm integral equation of the second kind.