What Is the Voltage Drop for 3 AWG at 1A and 300 Feet?

Running 1A through 3 AWG copper for 300 feet on a single-phase / DC circuit produces a 0.147-volt drop. On a 120V source that is 0.1225%; on 240V it is 0.0613%. NEC 210.19(A) Informational Note 4 recommends keeping branch-circuit drop at or below 3% and total feeder+branch drop at or below 5%, these are performance recommendations, not code requirements.

3 AWG, 1A, 300ft · single-phase / DC

0.147 V drop (0.1225% on 120V)

On 120V circuit0.1225%

On 240V circuit0.0613%

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 AWG

Amps

Feet

Drop @ 120V

0.15V (0.12%)

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 × 300 × 1 × 0.245) ÷ 1000 = 0.147 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: (0.147 ÷ 120) × 100 = 0.1225%

On 240V: (0.147 ÷ 240) × 100 = 0.0613%

How This Estimate Changes with Run Length and Gauge

Gauge Check

3 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 AWG at 1A at different distances:

Distance	Drop (V)	% on 120V	% on 240V	NEC (120V)
25ft	0.0123V	0.0102%	0.005104%	OK
50ft	0.0245V	0.0204%	0.0102%	OK
75ft	0.0368V	0.0306%	0.0153%	OK
100ft	0.049V	0.0408%	0.0204%	OK
150ft	0.0735V	0.0613%	0.0306%	OK
200ft	0.098V	0.0817%	0.0408%	OK
300ft	0.147V	0.1225%	0.0613%	OK

Same Run, Different Wire Gauges

How does wire gauge affect voltage drop for 1A at 300 feet on 120V single-phase / DC? Only gauges whose branch-circuit OCP cap is at or above the 1A 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	0.147V	0.1225%	0.0613%	OK
2 AWG	0.1164V	0.097%	0.0485%	OK
1 AWG	0.0924V	0.077%	0.0385%	OK
1/0 AWG	0.0732V	0.061%	0.0305%	OK
2/0 AWG	0.058V	0.0483%	0.0242%	OK
3/0 AWG	0.046V	0.0383%	0.0192%	OK

Related Calculations

cable Wire size: 1A, 300ft bolt Watts to amps calculator functions Voltage drop formula

Frequently Asked Questions

What is the voltage drop for 3 AWG at 1A and 300ft?expand_more

3 AWG carrying 1A over 300ft has a 0.147V drop (0.1225% on 120V). Reference: 0.0613% 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 0.0613% on 240V versus 0.1225% 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 AWG meet the 3% drop target at 1A and 300ft on 120V?expand_more

On 120V, this run sits at 0.1225%, 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 AWG for this run?expand_more

3 AWG already sits within the 3% branch-circuit drop target at these inputs (0.1225% 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.