Solar PV Cable Sizing

PV cable sizing presents unique challenges compared to conventional AC circuit design. DC string cables operate at high voltages (up to 1,500V for utility-scale systems) and carry the short-circuit current of the connected panels — which is only marginally higher than the operating current, making conventional overcurrent protection impractical for string cables. The design current is typically taken as 1.25 × Isc (short-circuit current of the string) to account for irradiance levels exceeding standard test conditions. Ambient temperatures near roof-mounted panels can exceed 70°C, requiring significant derating from tabulated values at 30°C. Cable insulation must be rated for UV exposure, and double-insulated cables (often designated H1Z2Z2-K) are required for DC circuits. Voltage drop is particularly important in large arrays where long cable runs to the inverter can waste valuable generated energy. IEC 62548 requires voltage drop to be limited so that power losses remain economically acceptable — typically below 1–2% for string cables and 1% for main DC cables. Earth fault detection requirements also influence conductor selection and earthing arrangements.