Fusing currents in composite cables are calculated by coupling the non-linear heat equation with the calculation of the joules heating in a non-linear finite element process that includes conduction and radiation effects. The method is verified using analytical formulas available for simple copper cables. The method is useful in multi-material composite cables as well as in conductors of arbitrary cross section such as traces on printed circuit boards where analytic formulas are not available. It is also useful for the calculation of temperatures and temperature distributions in power lines or any other current-carrying conductor. For short fusing times, the effects of conduction and radiation are negligible, simplifying the solution.Index Terms-Coupled problems, finite element analysis, fusing currents.