Proper feeder cable size depends on load, distance, and voltage drop considerations. Copper or aluminum conductor choice also influences wire size. Professional electrical wire sizing tool based on National Electrical Code (NEC) standards. Supports both NEC (USA) and CEC (Canada) with appropriate derating factors for temperature and conduit fill conditions. The calculator. A subpanel is a secondary electrical distribution point that receives power from your main service panel, allowing you to extend circuits to a different area of your home, garage, or workshop. The wires connecting the main panel to the subpanel are called feeder conductors, and their correct sizing. The NEC (National Electrical Code) provides guidance on how to size wires correctly for feeders and subpanels. Choosing the correct subpanel wire size ensures safety, prevents overheating, and keeps. Electrical feeder sizing is one of the most critical calculations in any electrical installation, yet it's often misunderstood even by experienced professionals.