4 AWG at 100A and 150 Feet: Ampacity-Invalid Reference Calculation
Reference voltage-drop calculation only. 4 AWG is NEC-capped at 85A branch-circuit OCP per NEC 240.4(D) (75°C ampacity 85A), so 100A on this gauge fails the ampacity check before voltage drop ever enters the conversation. Do not use the number below as an install spec. The 9.24-volt reference drop at 100A through 4 AWG for 150 feet is still a valid I×R calculation across the conductor, which is why this page renders it, but it is a reference-only figure and not a permission slip to run that current on that gauge.
Use this citation when referencing this page.
Circuit basis: This uses the single-phase / DC round-trip formula (factor of 2) for the voltage drop across the two circuit conductors. For a three-phase line-to-line run use the three-phase version of the page (append ?type=3ph). Switch to the three-phase version →
Assumes a 120V source on a single-phase / DC circuit. Use the circuit-basis link above to switch between single-phase/DC and three-phase.
Voltage Drop Formula (single-phase / DC)
Vdrop = (2 × L × I × R) ÷ 1000
DC and single-phase AC use the round-trip factor of 2. Current travels out to the load on one conductor and returns on another.
For a three-phase circuit at the same amps and distance, see the three-phase version (uses √3 instead of 2, so the drop is about 13.4% lower).
Percentage
%VD = (Vdrop ÷ Vsource) × 100
How This Estimate Changes with Run Length and Gauge
Gauge That Meets the 3% Target
4 AWG can't carry the 100A load in the first place, its branch-circuit OCP cap is 85A under typical conditions. The smallest gauge in our table that clears both the ampacity cap and the 3% drop target at these inputs is 2/0 AWG. Run the full wire-size calculator for run length, material, and drop-target variations.
Impact of Distance
Voltage drop is proportional to distance. Here is 4 AWG at 100A at different distances:
| Distance | Drop (V) | % on 120V | % on 240V | NEC (120V) |
|---|---|---|---|---|
| 25ft | 1.54V | 1.28% | 0.6417% | OK |
| 50ft | 3.08V | 2.57% | 1.28% | OK |
| 75ft | 4.62V | 3.85% | 1.93% | Caution |
| 100ft | 6.16V | 5.13% | 2.57% | Past 5% |
| 150ft | 9.24V | 7.7% | 3.85% | Past 5% |
| 200ft | 12.32V | 10.27% | 5.13% | Past 5% |
| 300ft | 18.48V | 15.4% | 7.7% | Past 5% |
Same Run, Different Wire Gauges
How does wire gauge affect voltage drop for 100A at 150 feet on 120V single-phase / DC? Only gauges whose branch-circuit OCP cap is at or above the 100A load are listed, since thinner gauges would fail the ampacity check before drop even matters.
| Gauge | Drop (V) | % on 120V | % on 240V | 3% Target (120V) |
|---|---|---|---|---|
| 3 AWG | 7.35V | 6.13% | 3.06% | Past 5% |
| 2 AWG | 5.82V | 4.85% | 2.43% | Caution |
| 1 AWG | 4.62V | 3.85% | 1.93% | Caution |
| 1/0 AWG | 3.66V | 3.05% | 1.53% | Caution |
| 2/0 AWG | 2.9V | 2.42% | 1.21% | OK |
| 3/0 AWG | 2.3V | 1.92% | 0.9575% | OK |
| 4/0 AWG | 1.82V | 1.52% | 0.76% | OK |
| 250 kcmil | 1.55V | 1.29% | 0.6437% | OK |
| 300 kcmil | 1.29V | 1.07% | 0.5363% | OK |
| 350 kcmil | 1.1V | 0.9175% | 0.4587% | OK |
| 500 kcmil | 0.774V | 0.645% | 0.3225% | OK |
| 750 kcmil | 0.513V | 0.4275% | 0.2138% | OK |