The current rating of paper-insulated power cables

The mathematical formulae and methods adopted for computing the permissible continuous rating of power cables are outlined, and examples for cables installed under specified conditions are worked out. Three methods of installation are recognized, viz. laid direct in the ground, pulled into ducts, in free air, indoors and outdoors, but protected from direct solar radiation. Tabular and graphical data, incl. temperature limits, thermal resistances and grouping factors for various types of cables, and comparative values for the current ratings for the various conditions, are given.