The type of network usually found in practice, i.e. one feeding scattered loads and having a complicated lay-out, is nearly always neglected, or at best receives summary treatment, in literature dealing with the subject of line calculations. The fundamental principles are here briefly reviewed, and methods based on the principle of superposition are described, enabling problems of any degree of complexity to be solved by successive approximation. The work involved in the solution is much less than that necessitated by a direct method, as the limits of accuracy of the data are generally fairly wide. The calculation of short-circuit currents and of their heating effect is also described and examples are given.