A study of the performance of power cables installed inside non-metallic ducts is presentedhere. Cable capacity calculations for this type of installation are done. The thermal analysisof cables inside ducts which are installed in air as riser or buried in soils is presented.According to IEC 60287 cables can be installed in fibre ducts in concrete layer surroundedby the soil, in this article it is proposed to install the cables in PVC ducts directly buried inthe soil. Based on IEC 60287-1-3 and IEC 60853-2 standards proposed models in steadystate and dynamic cable loadings are constructed. The proposed equivalent thermal modelsare used in the calculations of the cable components temperature for cables installed inducts. It is concluded that very high increase in cable conductor temperature is observedwhen the cable is installed in duct and used as riser or even when it is installed in duct buriedin soil. Significant decrease in the temperature of the cable conductor can be noticed whenthe cable is directly buried in the soil compared with that installed in ducts.