The most fundamental requirement is that the cable must carry the continuous load current without exceeding the temperature rating of its insulation. For example, XLPE (cross-linked polyethylene) insulation is commonly rated for 90∘C90 raised to the composed with power C Medium Voltage Cable 101: Understanding the Basics
For motor loads, a drop exceeding 5% at starting can cause torque issues. Capacitor banks and synchronous condensers are sometimes added instead of increasing cable size. mv cable sizing
