Wire Voltage Drop Calculator
NIST Material Constants · NEC Compliance Checks
Calculated Electrical Output
Metric Description
Calculated Output
Target Baseline
NEC Rating
Calculated Voltage Drop
6.32 V
Voltage Drop Percentage
5.27 %
Load Terminal Voltage
113.68 V
Circular Mil Rating
6,530 CM
NEC Code Compliance: Over 3% branch limit!
⚠ CODE EXCEEDED
Mathematical Voltage Drop Equations
This calculator implements standard branch-circuit calculations using Ohm's Law and conductor resistivity metrics ($K$ factors):
Single-Phase Formulas:
Voltage Drop (V_drop) = (2 × K × I × L) ÷ CM
Three-Phase Formulas:
Voltage Drop (V_drop) = (1.732 × K × I × L) ÷ CM
Voltage Drop (V_drop) = (2 × K × I × L) ÷ CM
Three-Phase Formulas:
Voltage Drop (V_drop) = (1.732 × K × I × L) ÷ CM
Where:
- K (Resistivity Factor): Constant representing resistance of one circular-mil foot of conductor. Copper is valued at exactly 12.9 ohms, while aluminum is valued at 21.2 ohms at 75°C standard temperature.
- I: Current load in amperes passing through the wire.
- L: One-way distance of the wire run from power source to load (in feet).
- CM: Circular mil area of the chosen wire size.
AWG Circular Mil Size Reference Chart
| Wire Gauge (AWG) | Area (Circular Mils) | Resistance per 1k Ft (Cu) | Max Ampacity (75°C) |
|---|---|---|---|
| 14 AWG | 4,110 | 3.07 ohms | 15A |
| 12 AWG | 6,530 | 1.93 ohms | 20A |
| 10 AWG | 10,380 | 1.24 ohms | 30A |
| 8 AWG | 16,510 | 0.778 ohms | 50A |
| 6 AWG | 26,240 | 0.491 ohms | 65A |
| 4 AWG | 41,740 | 0.308 ohms | 85A |
| 2 AWG | 66,360 | 0.194 ohms | 115A |