Cable sizing for EV chargers and fast chargers
Determine cable size, protection and voltage drop from power, distance, installation method and environment.
Calculate from current, not kilowatts alone
First determine the maximum continuous input current of the exact unit and configuration. A 22 kW AC charger typically draws 32 A per phase. For DC systems use the grid input in the technical sheet, because output power and grid current are not one-to-one.
Correct for length and installation method
Check current capacity for copper or aluminium, loaded conductors, ambient temperature, grouping, soil temperature and installation in conduit or cable tray. A cable in free air carries more current than the same cable in a warm, crowded bundle.
Calculate voltage drop and fault conditions
Calculate voltage drop over the complete route and reserve margin for the rest of the installation. Also verify fault loop and protective device disconnection time. For long DC routes between cabinet and dispenser, follow manufacturer limits for distance and cable loss.
Record the final selection
Rules of thumb are only suitable for an initial estimate. The installer completes the final calculation under local standards, selectivity and the technical sheet. Record cable type, cross-section, length, installation method, protection and calculated voltage drop.