IEC 60853-3 Ed. 1.0 b:2002

Gives a method for calculating the cyclic rating factor, for cables of all voltages, where partial drying out of the surrounding soil is anticipated. The method is based on one of the three methods published in a CIGRE document. The method is applicable to any type of cable, but it is recommended that it should be applied only to installations of one multi-core cable or to three single-core cables or to groups of circuits where the intercircuit spacing is sufficient to permit free vertical movement of soil moisture between the zones of dry soil associated with each circuit. This Standard does not preclude the use of other methods of calculation where full details of the load cycle are not known. The method assumes that the entire region surrounding a cable or cables has uniform thermal characteristics prior to drying out; the only non-uniformity being that caused by drying. As a consequence the method should not be applied, without further consideration, to installations where special backfills, having properties different from the site soil, are used.