Calculadora de caída de voltaje

1. Área del cable (circular mils)
   (5 × 92^((36 − AWG) ÷ 39))² circular mils
   12 AWG = 6,530
2. Resistencia por 1,000 ft
   K ÷ circular mils × 1.02 stranding × 1,000
   12.61 ÷ 6530 × 1.02 × 1,000 = 1.9701
3. Caída de voltaje
   2 × one-way ft × amps × Ω per 1,000 ft ÷ 1,000
   2 × 100 × 20 × 1.9701 ÷ 1,000 = 7.88
4. Porcentaje de caída
   drop ÷ source volts × 100
   7.88 ÷ 120 × 100 = 6.57%
5. Voltaje en la carga
   source − drop
   120 − 7.88 = 112.1

De dónde salen los números

• Wire area (AWG): d = 0.005" × 92^((36 − AWG) ÷ 39); circular mils = (d in mils)²; 1/0 = AWG 0, 4/0 = AWG −3; kcmil sizes are thousands of circular milsThe AWG definition (ASTM B258). 12 AWG = 6,530 cmil, 4/0 = 211,600 cmil — the same areas NEC Chapter 9 Table 8 lists.
• Resistance at 75 °C: K = 12.61 Ω·cmil/ft copper, 20.77 aluminum; × 1.02 for strandingWorked out from the conductivities NEC Chapter 9 Table 8 says it used (Note 4: copper 100% IACS, aluminum 61%): 10.371 Ω·cmil/ft at 20 °C ÷ IACS × (1 + α × 55 °C), α = 0.00393 copper, 0.00403 aluminum. Every size lands within 0.5% of Table 8's stranded uncoated-copper and aluminum columns (e.g. 12 AWG Cu 1.97 vs 1.98; 4/0 Al 0.1001 vs 0.100). DC resistance only — reactance is ignored, which understates drop on big AC feeders at low power factor (Table 9 covers that).Fuente
• Voltage drop: Single-phase: 2 × L × I × R ÷ 1,000 · Three-phase: √3 × L × I × R ÷ 1,000 (L = one-way feet, R = Ω per 1,000 ft)Ohm's law over the wire. Single-phase current goes out and back (2 × L); balanced three-phase line-to-line drop is √3 × the drop in one wire.
• 3% / 5% target: 3% on a branch circuit or feeder, 5% total for both — a recommendation, not a requirementNEC 210.19(A) Informational Note No. 4 (branch circuits) and 215.2(A) Informational Note No. 2 (feeders) in the 2017–2020 editions; the numbering moves in later editions. Informational notes are not enforceable code. This calculator does NOT size wire for ampacity (NEC 310.16), terminal temperature or derating — check those, and have a licensed electrician verify.