This book addresses the problem of finding ampacities of underground cables. Although standard methods for solving this problem provide satisfactory results, however, these results are not always optimal and algorithms are not always convergent. This book takes these standard methods as a starting point and formulates the ampacity calculations as an optimization problem. The solution to this optimization problem gives the required ampacities, and is determined by utilizing the barrier method algorithm. This algorithm is implemented in FORTRAN-77 and used to obtain ampacity solutions for various cable configurations. The results are compared with ampacities obtained using standard methods, implemented in the CYMCAP commercial software package. The comparisons show that ampacity solutions obtained with the optimization method are at least equal and up to 15% greater than those obtained with the latter. Such an increase in total current loadings greatly improves the utilization efficiency of power cables.