Calculadora de queda de tensão

Voltage drop is the loss across wire resistance: V = I × R. For DC copper wire, resistance depends on length (round trip), cross-sectional area, and resistivity (ρ ≈ 1.68×10⁻⁸ Ω·m for copper at room temperature).

Long runs, thin wire, and high current increase drop — motors and inverters may underperform if supply voltage sags. National electrical codes specify maximum drops for branch circuits; this is a quick estimate, not a NEC compliance check.

Example: 10 A through 25 m one-way (50 m loop) of 2.5 mm² copper drops about 3.4 V. Size wire for your acceptable drop and local code.

Round-trip length matters: current travels out and back, so a 25 m one-way run uses 50 m of conductor in the resistance calculation. Underestimating length is a common cause of surprise voltage sag on solar and RV installs.

Thicker wire (larger mm² or lower AWG number) lowers resistance and drop. If drop exceeds your device's minimum input voltage, step up wire size or move the power source closer.

Worked example with defaults: 10 A, 25 m one-way, 2.5 mm² cross-section → about 3.4 V drop on copper at room temperature. On a 12 V system that is roughly 28% of supply — often too high for sensitive loads.

NEC guidance often cites 3% maximum drop on branch circuits and 5% total from service to load — on a 12 V solar system, 3% is only 0.36 V, stricter than many appliance specs. Express drop as a percent of supply to compare against code-style limits. Three percent of 12 V is only 0.36 V — express drop as percent of supply when comparing against inverter low-voltage disconnect thresholds.

AWG wire sizes map to cross-section in mm²: 14 AWG ≈ 2.08 mm², 12 AWG ≈ 3.31 mm². If your spool is labeled AWG but the form asks mm², convert before entering — undersized wire is a common cause of nuisance undervoltage faults. 14 AWG ≈ 2.08 mm² and 12 AWG ≈ 3.31 mm² — convert spool labels before entering cross-section if your reel shows AWG only.

Aluminum conductors have higher resistivity than copper (~1.68 vs ~2.82 × 10⁻⁸ Ω·m at room temp). This tool assumes copper; swapping aluminum without adjusting resistivity underestimates drop — size aluminum one AWG larger than copper charts suggest. Aluminum needs roughly one AWG size larger than copper for similar drop — this copper model underestimates loss on aluminum conductors.