The calculation of cyclic rating factors for cables laid direct or in ducts

A simple method is presented for the rapid calculation of cyclic rating factors for cables laid direct in the ground and cables in ducts. The method may be applied without difficulty even in the case of complicated load curves, but for single-peaked load curves the calculation is especially simple. Tables of relevant functions are included as are additional tables of parameters for cables conforming to B.S. 480: 1954. Examples are given illustrating the ease and speed of the proposed method, together with the variation of cyclic rating factors with soil thermal constants.