What Is the Voltage Drop for 2/0 AWG at 31A and 125 Feet?

2/0 AWG copper carrying 31 amps over 125 feet on a single-phase / DC circuit drops 0.7494 volts (0.6245% on a 120V source). This sits within the 3% branch target and the 5% feeder+branch total target that NEC 210.19(A) Informational Note 4 cites. Both are planning targets, not code requirements.

2/0 AWG, 31A, 125ft · single-phase / DC

0.7494 V drop (0.6245% on 120V)

On 120V circuit0.6245%

On 240V circuit0.3123%

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 →

Gauge

2/0 AWG

Amps

Feet

Drop @ 120V

0.75V (0.62%)

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)

V_drop = (2 × L × I × R) ÷ 1000

(2 × 125 × 31 × 0.0967) ÷ 1000 = 0.7494 V

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 = (V_drop ÷ V_source) × 100

On 120V: (0.7494 ÷ 120) × 100 = 0.6245%

On 240V: (0.7494 ÷ 240) × 100 = 0.3123%

How This Estimate Changes with Run Length and Gauge

Gauge Check

2/0 AWG clears the 3% drop target at these inputs. A smaller conductor may also meet it with less margin. See the minimum gauge for this load and distance.

Impact of Distance

Voltage drop is proportional to distance. Here is 2/0 AWG at 31A at different distances:

Distance	Drop (V)	% on 120V	% on 240V	NEC (120V)
25ft	0.1499V	0.1249%	0.0625%	OK
50ft	0.2998V	0.2498%	0.1249%	OK
75ft	0.4497V	0.3747%	0.1874%	OK
100ft	0.5995V	0.4996%	0.2498%	OK
150ft	0.8993V	0.7494%	0.3747%	OK
200ft	1.2V	0.9992%	0.4996%	OK
300ft	1.8V	1.5%	0.7494%	OK

Same Run, Different Wire Gauges

How does wire gauge affect voltage drop for 31A at 125 feet on 120V single-phase / DC? Only gauges whose branch-circuit OCP cap is at or above the 31A 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)
2/0 AWG	0.7494V	0.6245%	0.3123%	OK
3/0 AWG	0.5937V	0.4947%	0.2474%	OK
4/0 AWG	0.4712V	0.3927%	0.1963%	OK
250 kcmil	0.3991V	0.3326%	0.1663%	OK
300 kcmil	0.3325V	0.2771%	0.1385%	OK
350 kcmil	0.2844V	0.237%	0.1185%	OK

Related Calculations

cable Wire size: 31A, 125ft bolt Watts to amps calculator functions Voltage drop formula

Frequently Asked Questions

What is the voltage drop for 2/0 AWG at 31A and 125ft?expand_more

2/0 AWG carrying 31A over 125ft has a 0.7494V drop (0.6245% on 120V). Reference: 0.3123% on 240V.

Is voltage drop worse on 120V or 240V?expand_more

Same wire, same amps, same distance: the volts dropped are identical. But the percentage is worse on 120V because the drop is a larger fraction of the source voltage. This run would be 0.3123% on 240V versus 0.6245% on 120V.

What wire gauge should I use instead of 2/0 AWG for this run?expand_more

2/0 AWG already sits within the 3% branch-circuit drop target at these inputs (0.6245% on 120V). Going to a larger gauge is only useful if you want more headroom for future load growth, longer runs, or tighter drop targets like the 5% feeder+branch total recommendation used in sensitive or motor-heavy installations.

Does 2/0 AWG meet the 3% drop target at 31A and 125ft on 120V?expand_more

On 120V, this run sits at 0.6245%, which is within the 3% branch and 5% feeder+branch total drop targets. NEC 210.19(A) Informational Note 4 cites 3% for branch circuits and 5% for total feeder+branch drop as performance recommendations, not hard code requirements.

Why does distance affect voltage drop?expand_more

Voltage drop is proportional to distance. The formula multiplies by 2 × the distance (out and back). Doubling the run doubles the drop.

This calculator provides estimates for reference purposes only. Always consult a licensed electrician and verify compliance with the National Electrical Code (NEC) and local electrical codes before performing any electrical work.