Cable selection is about choosing the appropriate type of conductor and selecting a suitable size/cross-section area/ diameter of the conductor according to the application. First, there is a need to understand the significance of cable sizing and selection. Then selection criteria will be discussed keeping in mind all the derating factors that might reduce cable ampacity. A law named Kelvin's law plays a vital role in the economic sizing of conductors, so it will also be explained here. Other than the size of conductor, different types of the conductor will be studied. Also, the cable shielding and insulation will be discussed at the end.