Voltage Drop Calculator
Evaluate branch circuit voltage loss and conductor resistance per National Electrical Code (NEC) Chapter 9 standards. Proper electrical distribution requires strict adherence to safety and efficiency metrics to prevent overheating, insulation breakdown, and equipment failure.
Use our professional-grade Voltage Drop Calculator below to instantly compute line loss, percentage drop, and terminal voltage based on conductor material, wire size, run distance, and load current.
Calculated Output & Compliance
Principles of Electrical Voltage Loss
Whenever electrical current passes through a metallic pathway, the conductor’s inherent physical resistance converts a fraction of electrical potential into dissipated thermal energy. Over short distances this reduction is negligible, but extended feeder runs and high-amperage equipment can experience dramatic reductions in available operating voltage.
Calculation Mechanics
The mathematical evaluation of line loss relies upon the conductor length, load demand, and DC ohmic resistance extracted from standardized reference tables:
Two-Wire / Single-Phase Installations:
Voltage Drop = 2 × Current (A) × [Resistance (Ω/kft) / 1000] × Distance (ft)
Three-Phase Installations:
Voltage Drop = 1.732 × Current (A) × [Resistance (Ω/kft) / 1000] × Distance (ft)
NEC Chapter 9 Table 8 Reference Data (at 75°C)
The following metrics represent standard values for uncoated copper and aluminum conductors commonly used in building wiring:
| Conductor Gauge | Cross-Section (cmil) | Copper Resistance (Ω/kft) | Aluminum Resistance (Ω/kft) |
|---|---|---|---|
| 14 AWG | 4,110 | 3.07 | 5.06 |
| 12 AWG | 6,530 | 1.93 | 3.18 |
| 10 AWG | 10,380 | 1.21 | 2.00 |
| 8 AWG | 16,510 | 0.764 | 1.26 |
| 6 AWG | 26,240 | 0.491 | 0.808 |
| 4 AWG | 41,740 | 0.308 | 0.508 |
Frequently Asked Questions
Why should branch circuits aim for a maximum 3% drop?
Keeping branch losses under 3% ensures connected hardware operates within design tolerances, preventing overheating and premature failure.
How should I correct excessive voltage drop?
The simplest remediation is stepping up to a larger wire gauge, which lowers total line resistance and restores terminal voltage.
Organize Long Electrical Runs
Running heavier gauge cables to curb voltage drop? Secure subpanel feeders and heavy conduits cleanly with our parametric, 3D-printable cable cleats.
