Calculates voltage drop across a conductor run given current, wire length, AWG gauge, system voltage, and conductor material (copper or aluminum). Computes round-trip resistance, voltage drop in volts and percent, voltage at the load end, power dissipated in the wire, and NEC compliance flags (3% max for branch circuits, 5% max for feeders). Use this after wire_gauge to verify a specific gauge meets requirements, or to evaluate an existing installation. Critical for solar panel string wiring, EV charger circuits, low-voltage lighting, and any long DC or AC cable run where resistive losses matter.