Calculate voltage drop in electrical circuits based on wire size, distance, and load current. Supports NEC data, custom resistance values, and various wire materials.
Voltage drop is the decrease in electrical potential along the path of a current flowing in an electrical circuit. When electrical current flows through a wire, it encounters resistance, which causes a reduction in voltage from the source to the load.
Excessive voltage drop can cause significant problems in electrical systems, including poor performance of electrical equipment, reduced efficiency, and potential safety hazards. Understanding and calculating voltage drop is essential for proper electrical system design.
Where: I = Current (amps), R = Resistance (ohms)
Where: I = Current, R = Resistance per unit length, L = One-way length
Where: √3 ≈ 1.732 (for balanced three-phase loads)
The National Electrical Code (NEC) recommends that voltage drop should not exceed:
| AWG | Diameter (inch) |
Diameter (mm) |
Area (kcmil) |
Area (mm²) |
Copper Resistance (Ω/km) |
Copper Resistance (Ω/1000ft) |
|---|---|---|---|---|---|---|
| 4/0 | 0.4600 | 11.684 | 212 | 107 | 0.1608 | 0.04901 |
| 3/0 | 0.4096 | 10.404 | 168 | 85.0 | 0.2028 | 0.06180 |
| 2/0 | 0.3648 | 9.266 | 133 | 67.4 | 0.2557 | 0.07793 |
| 1/0 | 0.3249 | 8.252 | 106 | 53.5 | 0.3224 | 0.09827 |
| 1 | 0.2893 | 7.348 | 83.7 | 42.4 | 0.4066 | 0.1239 |
| 2 | 0.2576 | 6.544 | 66.4 | 33.6 | 0.5127 | 0.1563 |
| 3 | 0.2294 | 5.827 | 52.6 | 26.7 | 0.6465 | 0.1970 |
| 4 | 0.2043 | 5.189 | 41.7 | 21.2 | 0.8152 | 0.2485 |
| 6 | 0.1620 | 4.115 | 26.3 | 13.3 | 1.296 | 0.3951 |
| 8 | 0.1285 | 3.264 | 16.5 | 8.37 | 2.061 | 0.6282 |
| 10 | 0.1019 | 2.588 | 10.4 | 5.26 | 3.277 | 0.9989 |
| 12 | 0.0808 | 2.053 | 6.53 | 3.31 | 5.211 | 1.588 |
| 14 | 0.0641 | 1.628 | 4.11 | 2.08 | 8.286 | 2.525 |
Excessive voltage drop in electrical circuits can cause several problems:
Lighting Issues: Incandescent bulbs dim, fluorescent lights may flicker or fail to start, and LED lights may experience reduced lifespan or color shifting.
Motor Performance: Motors run hotter, have reduced starting torque, draw higher current, and may experience premature failure. Voltage drop can significantly affect motor efficiency and lifespan.
Heating Equipment: Electric heaters produce less heat output, and resistance-type loads operate at reduced capacity when voltage is below rated levels.
Electronic Equipment: Sensitive electronic devices may malfunction, have reduced performance, or suffer damage from insufficient or unstable voltage supply.
Increase Wire Size: Using larger conductors (smaller AWG numbers) reduces resistance and voltage drop. This is often the most practical solution for new installations.
Reduce Circuit Length: Shorter runs have less resistance. Consider relocating panels or using sub-panels closer to loads when possible.
Use Higher Voltage: Higher voltage systems have proportionally lower current for the same power, reducing voltage drop. Consider 240V instead of 120V for high-power loads.
Parallel Conductors: Running multiple conductors in parallel reduces the total resistance of the circuit, though this requires careful installation and consideration of current sharing.