What Is the Voltage Drop for 3 AWG at 77A and 75 Feet?

3 AWG at 77A and 75 feet: 2.83V drop (2.36% on 120V), computed on the single-phase / DC basis. Every conductor has resistance, and longer runs at higher currents drop more voltage. Use this calculation to check whether your run clears the 3% branch-circuit drop target before pulling wire.

3 AWG, 77A, 75ft · single-phase / DC

2.83 V drop (2.36% on 120V)

On 120V circuit2.36%

On 240V circuit1.18%

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

2.83V (2.36%)

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 × 75 × 77 × 0.245) ÷ 1000 = 2.83 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: (2.83 ÷ 120) × 100 = 2.36%

On 240V: (2.83 ÷ 240) × 100 = 1.18%

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 77A at different distances:

Distance	Drop (V)	% on 120V	% on 240V	NEC (120V)
25ft	0.9433V	0.786%	0.393%	OK
50ft	1.89V	1.57%	0.786%	OK
75ft	2.83V	2.36%	1.18%	OK
100ft	3.77V	3.14%	1.57%	Caution
150ft	5.66V	4.72%	2.36%	Caution
200ft	7.55V	6.29%	3.14%	Past 5%
300ft	11.32V	9.43%	4.72%	Past 5%

Same Run, Different Wire Gauges

How does wire gauge affect voltage drop for 77A at 75 feet on 120V single-phase / DC? Only gauges whose branch-circuit OCP cap is at or above the 77A 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	2.83V	2.36%	1.18%	OK
2 AWG	2.24V	1.87%	0.9336%	OK
1 AWG	1.78V	1.48%	0.7411%	OK
1/0 AWG	1.41V	1.17%	0.5871%	OK
2/0 AWG	1.12V	0.9307%	0.4654%	OK
3/0 AWG	0.8847V	0.7373%	0.3686%	OK

Related Calculations

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Frequently Asked Questions

What is the voltage drop for 3 AWG at 77A and 75ft?expand_more

3 AWG carrying 77A over 75ft has a 2.83V drop (2.36% on 120V). Reference: 1.18% 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 1.18% on 240V versus 2.36% on 120V.

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 (2.36% 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 3 AWG meet the 3% drop target at 77A and 75ft on 120V?expand_more

On 120V, this run sits at 2.36%, 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.