What Is the Voltage Drop for 2/0 AWG at 135A and 150 Feet?
2/0 AWG copper carrying 135 amps over 150 feet on a single-phase / DC circuit drops 3.92 volts (3.26% on a 120V source). This sits past the 3% target NEC 210.19(A) Informational Note 4 cites for branch circuits, but within the 5% target for feeder+branch total. Which one applies depends on whether this run is a branch circuit, a feeder, or a feeder+branch combined: if it's a branch circuit, it's past target; if it's a feeder alone or part of a feeder+branch combined system, the 5% total is the figure to check against whatever the upstream drop adds. Both are planning targets, not code requirements.
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
The smallest gauge in our table that clears the 3% drop target at 135A over 150ft on 120V is 3/0 AWG. Shorter runs, higher source voltage, or a higher drop tolerance (feeder-only applications often accept up to 5%) can change the pick. Run the full wire-size calculator with your actual variables.
Impact of Distance
Voltage drop is proportional to distance. Here is 2/0 AWG at 135A at different distances:
| Distance | Drop (V) | % on 120V | % on 240V | NEC (120V) |
|---|---|---|---|---|
| 25ft | 0.6527V | 0.5439% | 0.272% | OK |
| 50ft | 1.31V | 1.09% | 0.5439% | OK |
| 75ft | 1.96V | 1.63% | 0.8159% | OK |
| 100ft | 2.61V | 2.18% | 1.09% | OK |
| 150ft | 3.92V | 3.26% | 1.63% | Caution |
| 200ft | 5.22V | 4.35% | 2.18% | Caution |
| 300ft | 7.83V | 6.53% | 3.26% | Past 5% |
Same Run, Different Wire Gauges
How does wire gauge affect voltage drop for 135A at 150 feet on 120V single-phase / DC? Only gauges whose branch-circuit OCP cap is at or above the 135A load are listed, since thinner gauges would fail the ampacity check before drop even matters.