What Is the Voltage Drop for 3/0 AWG at 56A and 250 Feet?

3/0 AWG copper carrying 56 amps over 250 feet on a single-phase / DC circuit drops 2.14 volts (1.79% 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.

3/0 AWG, 56A, 250ft · single-phase / DC

2.14 V drop (1.79% on 120V)

On 120V circuit1.79%

On 240V circuit0.8937%

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

3/0 AWG

Amps

Feet

Drop @ 120V

2.14V (1.79%)

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 × 250 × 56 × 0.0766) ÷ 1000 = 2.14 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: (2.14 ÷ 120) × 100 = 1.79%

On 240V: (2.14 ÷ 240) × 100 = 0.8937%

How This Estimate Changes with Run Length and Gauge

Gauge Check

3/0 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 3/0 AWG at 56A at different distances:

Distance	Drop (V)	% on 120V	% on 240V	NEC (120V)
25ft	0.2145V	0.1787%	0.0894%	OK
50ft	0.429V	0.3575%	0.1787%	OK
75ft	0.6434V	0.5362%	0.2681%	OK
100ft	0.8579V	0.7149%	0.3575%	OK
150ft	1.29V	1.07%	0.5362%	OK
200ft	1.72V	1.43%	0.7149%	OK
300ft	2.57V	2.14%	1.07%	OK

Same Run, Different Wire Gauges

How does wire gauge affect voltage drop for 56A at 250 feet on 120V single-phase / DC? Only gauges whose branch-circuit OCP cap is at or above the 56A 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)
3/0 AWG	2.14V	1.79%	0.8937%	OK
4/0 AWG	1.7V	1.42%	0.7093%	OK
250 kcmil	1.44V	1.2%	0.6008%	OK
300 kcmil	1.2V	1%	0.5005%	OK
350 kcmil	1.03V	0.8563%	0.4282%	OK
500 kcmil	0.7224V	0.602%	0.301%	OK

Related Calculations

cable Wire size: 56A, 250ft bolt Watts to amps calculator functions Voltage drop formula

Frequently Asked Questions

What is the voltage drop for 3/0 AWG at 56A and 250ft?expand_more

3/0 AWG carrying 56A over 250ft has a 2.14V drop (1.79% on 120V). Reference: 0.8937% 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 0.8937% on 240V versus 1.79% on 120V.

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.

Does 3/0 AWG meet the 3% drop target at 56A and 250ft on 120V?expand_more

On 120V, this run sits at 1.79%, 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.

What wire gauge should I use instead of 3/0 AWG for this run?expand_more

3/0 AWG already sits within the 3% branch-circuit drop target at these inputs (1.79% 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.

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.