Voltage Drop Calculator
Calculate the electrical voltage drop and percentage loss for copper and aluminum conductors. Supports DC, single-phase AC, and three-phase AC systems with real-time interactive sliders, circuit diagrams, and wire size comparisons per NFPA 70-2026.
Calculator Inputs
NEC recommends a maximum of 3% drop for branch circuits and 5% total for feeder and branch combined.
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Set your inputs, then run the calculation.
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Conductor Resistance Reference Chart
DC resistance values in Ohms (Ω) per 1,000 feet at 75°C (167°F) from NEC Chapter 9, Table 8. These values form the foundation of standard voltage drop calculations.
| Conductor Size | Copper Resistance (Ω/1k ft) | Aluminum Resistance (Ω/1k ft) | Circular Mils (cmil) |
|---|---|---|---|
| 14 AWG | 3.14 | — | 4,110 |
| 12 AWG | 1.98 | 3.25 | 6,530 |
| 10 AWG | 1.24 | 2.04 | 10,380 |
| 8 AWG | 0.778 | 1.28 | 16,510 |
| 6 AWG | 0.491 | 0.808 | 26,240 |
| 4 AWG | 0.308 | 0.508 | 41,740 |
| 2 AWG | 0.194 | 0.319 | 66,360 |
| 1/0 AWG | 0.122 | 0.201 | 105,600 |
| 2/0 AWG | 0.0967 | 0.159 | 133,100 |
| 4/0 AWG | 0.0608 | 0.1 | 211,600 |
| 350 kcmil | 0.0367 | 0.0605 | 350,000 |
| 500 kcmil | 0.0276 | 0.0453 | 500,000 |
Source: NFPA 70-2026, Chapter 9, Table 8. Resistance values are for uncoated, stranded conductors at 75°C.
How to Reduce Voltage Drop in Your Circuits
If your voltage drop exceeds the recommended limits, there are several standard engineering methods to mitigate the loss and restore voltage stability at the load:
1. Increase Conductor Size
The most common and direct solution. Upsizing to a larger wire gauge (e.g., from #6 AWG to #4 AWG) reduces the resistance per foot, lowering the voltage drop. Use our comparison chart to find the exact size that satisfies your limit.
2. Run Parallel Conductors
For high-current industrial circuits, running multiple parallel wires per phase (e.g., two runs of 2/0 AWG instead of one run of 250 kcmil) splits the load current and halves the effective circuit resistance, substantially reducing drop.
3. Increase System Voltage
For a given power level, increasing the system voltage (e.g., from 120V to 240V, or 208V to 480V) proportionally reduces the current (Amps) needed to deliver that power. Lower current results in exponentially smaller voltage drop percentage.
Frequently Asked Questions
What is voltage drop and why does it occur?
Voltage drop is the decrease of electrical potential along the path of a current flowing in an electrical circuit. It occurs because all conductors (wires) have internal electrical resistance. As current flows through this resistance, some energy is lost as heat, resulting in a lower voltage at the load end of the circuit compared to the source.
What is the maximum allowable voltage drop recommended by the NEC?
The National Electrical Code (NEC) recommends a maximum voltage drop of 3% for branch circuits, and a maximum of 5% total for the combined feeder and branch circuits. While these guidelines are recommendations (not strict mandates in all jurisdictions), maintaining these limits is critical for equipment efficiency, longevity, and safety.
How does phase type affect voltage drop calculations?
Phase type determines the multiplier used in the voltage drop formula. For DC and single-phase AC circuits, current travels out and back, so the multiplier is 2. For balanced three-phase AC circuits, the phase currents offset each other, resulting in a smaller multiplier of 1.732 (the square root of 3). This means three-phase systems are inherently more efficient and experience less voltage drop for the same load and wire size.
Does power factor affect voltage drop?
Yes, in AC systems, the power factor (PF) affects the voltage drop. The power factor represents the phase difference between voltage and current. A lower power factor increases the current required to deliver the same real power, which in turn increases the voltage drop. Our calculator accounts for power factor in AC calculations using the standard formula.
How do parallel runs reduce voltage drop?
Running multiple conductors in parallel per phase divides the total current among the conductors and effectively reduces the overall circuit resistance. For example, using two parallel conductors per phase cuts the circuit resistance in half, which directly reduces the voltage drop by 50%. Parallel runs are common in high-current commercial and industrial applications.
Why is aluminum wire more susceptible to voltage drop than copper?
Aluminum has a higher electrical resistivity than copper (about 1.6 times higher). Therefore, for a given wire gauge and length, an aluminum conductor will have higher resistance and experience more voltage drop than a copper conductor. To achieve the same voltage drop, aluminum conductors must typically be sized 1 to 2 gauges larger than copper.
Disclaimer: This calculator is provided for educational and informational purposes, referencing standard formulas and NFPA 70-2026 (National Electrical Code) tables. Results should be verified by a licensed electrical engineer or certified electrician prior to any physical installation. Local electrical codes and AHJ regulations may vary.