Determine con precisión la pérdida de energía en circuitos CC, CA monofásica y trifásica. Resultados instantáneos compatibles con NEC.
Una calculadora de caída de tensión determina exactamente cuánta energía eléctrica se pierde como calor cuando la corriente viaja por un cable desde la fuente hasta la carga.
Cada cable tiene resistencia natural y, en distancias largas, esta resistencia roba voltaje. Conocer la pérdida exacta ayuda a seleccionar el calibre de cable (AWG) correcto para que el equipo reciba suficiente energía.
Mejores prácticas para ingeniería profesional:
| Aplicación | Límite |
|---|---|
| Circuitos Derivados | 3% |
| Alimentadores | 2% |
| Sistema Total | 5% |
| Solar FV | 2% |
Más allá de la longitud y la corriente, estos factores afectan la caída:
Elegir el material adecuado para su proyecto:
| Característica | Cobre | Aluminio |
|---|---|---|
| Conductividad | 100% | 61% |
| Peso | Pesado | Ligero (30%) |
| Costo | Alto | Bajo |
| Uso | Interior/Pequeño | Servicio/Grande |
For DC strings, keep voltage drop under 2% to maximize energy yield. Over 25 years, a 1% higher efficiency adds up to significant financial returns.
In 12V systems, a 3.6V drop is **30%**. Critical equipment (GPS, Bilge pumps) requires staying under 3%, while lights can handle up to 10%.
Motors drawing high startup current (LRA) cause momentary massive voltage drops. Ensure steady-state drop is under 5% at motor terminals for 480V systems.
A unit of area equal to the area of a circle with a diameter of one mil (1/1000 inch). Used in the NEC to define wire cross-sections.
The maximum current, in amperes, that a conductor can carry continuously under conditions of use without exceeding its temperature rating.
Derived from the NEC Chapter 9, Table 8.
| AWG | Copper | Alum |
|---|---|---|
| 14 AWG | 3.14 | 5.14 |
| 12 AWG | 1.98 | 3.25 |
| 10 AWG | 1.24 | 2.04 |
| 8 AWG | 0.778 | 1.28 |
| Gauge | Feet |
|---|---|
| 14 AWG | 38 ft |
| 12 AWG | 60 ft |
| 10 AWG | 96 ft |
| 8 AWG | 154 ft |
Our engine uses the NEC-standard methodology. Here is how you can calculate it manually for a single-phase system:
Scenario: 120V circuit, 15 Amps, 100ft distance, using 12 AWG Copper (6,530 CM).
The K factor represents the resistance of a circular mil-foot of conductor (~12.9 for Copper, ~21.2 for Aluminum at 75°C).
The cross-sectional area of the wire size. Larger CM values result in lower voltage drop.
The actual load current in Amperes. Voltage drop is directly proportional to current.
The length of the conductor from source to load. For round-trip circuits, the formula uses a multiplier of 2.
Understanding voltage drop theory is important, but seeing how it applies to actual jobs is what separates professionals from amateurs. Below are the most common real-world scenarios electricians, engineers, and installers face daily.
A typical home with a 200A main panel located 50 feet from the utility transformer. Using 4/0 AWG copper, the voltage drop at full load on a 240V system is approximately 1.52V (0.63%) — well within NEC limits.
Running a 60A sub-panel to a detached garage 120 feet away on a 240V circuit requires at least 4 AWG copper or 2 AWG aluminum to keep voltage drop under 3%.
A 1 HP well pump drawing 10A at 240V, located 300 feet from the panel, needs 6 AWG copper minimum. Using 10 AWG would result in a 7.44V (3.1%) drop.
A Level 2 EV charger drawing 40A at 240V installed 80 feet from the panel requires 6 AWG copper. Using 8 AWG would result in a 4.98% drop.
A 20A lighting circuit at 277V running 250 feet. Using 10 AWG copper gives a drop of 6.2V (2.24%). At 120V, the percentage would jump to 5.17%.
A rooftop solar array producing 8.5A at 48V DC with a 150-foot run. Using 10 AWG results in a 2.11V (4.39%) drop. Upgrade to 6 AWG for 1.34% efficiency.
This comprehensive table covers every common wire gauge from 14 AWG to 4/0 AWG, showing resistance per 1,000 feet, circular mils, and maximum ampacity per NEC 310.16 at 75°C. No competitor provides this level of detail in a single reference.
| AWG | Circular Mils | Cu Ω/1000ft | Al Ω/1000ft | Cu Ampacity | Al Ampacity |
|---|---|---|---|---|---|
| 14 AWG | 4,110 | 3.14 | 5.17 | 15A | — |
| 12 AWG | 6,530 | 1.98 | 3.25 | 20A | 15A |
| 10 AWG | 10,380 | 1.24 | 2.04 | 30A | 25A |
| 8 AWG | 16,510 | 0.778 | 1.28 | 40A | 30A |
| 6 AWG | 26,240 | 0.491 | 0.808 | 55A | 40A |
| 4 AWG | 41,740 | 0.308 | 0.508 | 70A | 55A |
| 3 AWG | 52,620 | 0.245 | 0.403 | 85A | 65A |
| 2 AWG | 66,360 | 0.194 | 0.319 | 95A | 75A |
| 1 AWG | 83,690 | 0.154 | 0.253 | 110A | 85A |
| 1/0 AWG | 105,600 | 0.122 | 0.201 | 125A | 100A |
| 2/0 AWG | 133,100 | 0.0967 | 0.159 | 145A | 115A |
| 3/0 AWG | 167,800 | 0.0766 | 0.126 | 165A | 130A |
| 4/0 AWG | 211,600 | 0.0608 | 0.100 | 195A | 150A |
Source: NEC Chapter 9, Table 8 (DC Resistance at 75°C) and NEC Table 310.16 (Ampacity for 75°C rated conductors in raceway).
If your calculated or measured voltage drop exceeds the NEC-recommended 3% for branch circuits, follow this systematic troubleshooting process used by licensed electricians.
Use a true-RMS multimeter to measure voltage at the panel and load simultaneously. If the measured drop is significantly higher than calculated, you likely have a physical connection problem.
Loose lugs and corroded terminals are the #1 cause of unexpected drop. A single loose connection can add 2-5V of drop. Torque connections to manufacturer specifications.
Confirm the actual wire gauge matches the spec. In older homes, you may find 14 AWG on 20A circuits, or aluminum wiring that has higher resistance than expected.
If the run cannot be upsized, consider splitting the load across multiple circuits. Loading a 20A circuit to only 50% capacity will significantly reduce voltage drop.
Different applications have different tolerance levels for voltage drop. This comprehensive guide covers every major scenario, from residential to heavy industrial — information you won't find compiled anywhere else.
| Application | Typical Voltage | Max Drop % | Why It Matters |
|---|---|---|---|
| Residential Branch Circuit | 120/240V | 3% | Prevents flickering lights and appliance damage |
| Residential Feeder | 240V | 2% | Ensures sub-panels receive adequate voltage |
| Commercial Lighting | 277/480V | 3% | LED drivers are sensitive to input voltage variation |
| Motor Feeders | 480V | 3-5% | Motors draw 6-8x startup current; excess drop prevents starting |
| Solar PV DC String | 24-600V DC | 1-2% | Every % of drop directly reduces energy harvest and ROI |
| Solar PV AC Inverter Output | 240V | 2% | Utility interconnection standards require tight voltage regulation |
| EV Charger (Level 2) | 240V | 3% | Excess drop slows charging and may trip GFCI protection |
| Marine/Boat (Critical) | 12/24V DC | 3% | Navigation and bilge systems cannot tolerate low voltage |
| Marine/Boat (Non-Critical) | 12/24V DC | 10% | Interior lights and accessories are more tolerant |
| RV/Camper | 12V DC | 3% | Small voltage = big percentage; 0.36V drop is already 3% |
| Data Center | 208/480V | 1-2% | Servers and UPS systems require stable voltage input |
| Fire Alarm Systems | 24V DC | 10% | NFPA 72 allows higher drop but devices must still operate |
| Landscape Lighting | 12V AC | 5-10% | Low voltage means even small drops cause visible dimming |
| Agricultural/Farm | 240/480V | 3% | Long barn runs to irrigation pumps and grain dryers |
Wire resistance changes with temperature. The NEC standard resistance values are rated at 75°C, but real-world conditions vary. Use this correction factor table to adjust your voltage drop calculations for actual operating temperature.
| Temperature | Copper Factor | Aluminum Factor |
|---|---|---|
| 20°C (68°F) | 0.88 | 0.87 |
| 30°C (86°F) | 0.92 | 0.91 |
| 40°C (104°F) | 0.96 | 0.95 |
| 60°C (140°F) | 1.04 | 1.03 |
| 75°C (167°F) | 1.00 | 1.00 |
| 90°C (194°F) | 1.06 | 1.06 |
One of the most commonly misunderstood aspects of voltage drop is the difference between single-phase and three-phase calculations. Here's a detailed breakdown that explains exactly why the formulas differ and when to use each one.
The factor of 2 accounts for the round-trip path — current flows out on one conductor and returns on the other. This applies to all DC circuits and single-phase AC circuits (120V, 240V residential).
The factor of √3 (1.732) replaces the 2 because in a balanced 3-phase system, the return current is distributed among three conductors. This results in approximately 13.4% less voltage drop compared to a single-phase circuit with the same wire and load.
This quick-reference table shows the maximum one-way distance you can run copper wire before exceeding a 3% voltage drop. Essential for field electricians who need instant answers without a calculator.
| AWG | 10A @120V | 15A @120V | 20A @120V | 20A @240V | 30A @240V | 40A @240V |
|---|---|---|---|---|---|---|
| 14 AWG | 57 ft | 38 ft | — | — | — | — |
| 12 AWG | 91 ft | 60 ft | 45 ft | 91 ft | — | — |
| 10 AWG | 145 ft | 96 ft | 72 ft | 145 ft | 96 ft | — |
| 8 AWG | 231 ft | 154 ft | 115 ft | 231 ft | 154 ft | 115 ft |
| 6 AWG | 367 ft | 244 ft | 183 ft | 367 ft | 244 ft | 183 ft |
| 4 AWG | 584 ft | 389 ft | 292 ft | 584 ft | 389 ft | 292 ft |
Dashes (—) indicate the wire gauge does not have sufficient ampacity for that load per NEC 310.16.