6 AWG at 80A and 100 Feet: Ampacity-Invalid Reference Calculation

Reference voltage-drop calculation only. 6 AWG is NEC-capped at 65A branch-circuit OCP per NEC 240.4(D) (75°C ampacity 65A), so 80A on this gauge fails the ampacity check before voltage drop ever enters the conversation. Do not use the number below as an install spec. As a load-side reference, 6 AWG copper at 80 amps over 100 feet on a single-phase / DC circuit would drop 7.86 volts (6.55% on 120V, 3.27% on 240V).

6 AWG, 80A, 100ft · single-phase / DC · reference only, ampacity-invalid

7.86 V drop (6.55% on 120V)

On 120V circuit6.55%

On 240V circuit3.27%

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

6 AWG

Amps

Feet

Drop @ 120V

7.86V (6.55%)

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 × 100 × 80 × 0.491) ÷ 1000 = 7.86 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: (7.86 ÷ 120) × 100 = 6.55%

On 240V: (7.86 ÷ 240) × 100 = 3.27%

How This Estimate Changes with Run Length and Gauge

Gauge That Meets the 3% Target

6 AWG can't carry the 80A load in the first place, its branch-circuit OCP cap is 65A under typical conditions. The smallest gauge in our table that clears both the ampacity cap and the 3% drop target at these inputs is 2 AWG. Run the full wire-size calculator for run length, material, and drop-target variations.

Impact of Distance

Voltage drop is proportional to distance. Here is 6 AWG at 80A at different distances:

Distance	Drop (V)	% on 120V	% on 240V	NEC (120V)
25ft	1.96V	1.64%	0.8183%	OK
50ft	3.93V	3.27%	1.64%	Caution
75ft	5.89V	4.91%	2.46%	Caution
100ft	7.86V	6.55%	3.27%	Past 5%
150ft	11.78V	9.82%	4.91%	Past 5%
200ft	15.71V	13.09%	6.55%	Past 5%
300ft	23.57V	19.64%	9.82%	Past 5%

Same Run, Different Wire Gauges

How does wire gauge affect voltage drop for 80A at 100 feet on 120V single-phase / DC? Only gauges whose branch-circuit OCP cap is at or above the 80A 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)
4 AWG	4.93V	4.11%	2.05%	Caution
3 AWG	3.92V	3.27%	1.63%	Caution
2 AWG	3.1V	2.59%	1.29%	OK
1 AWG	2.46V	2.05%	1.03%	OK
1/0 AWG	1.95V	1.63%	0.8133%	OK
2/0 AWG	1.55V	1.29%	0.6447%	OK
3/0 AWG	1.23V	1.02%	0.5107%	OK
4/0 AWG	0.9728V	0.8107%	0.4053%	OK
250 kcmil	0.824V	0.6867%	0.3433%	OK
300 kcmil	0.6864V	0.572%	0.286%	OK
350 kcmil	0.5872V	0.4893%	0.2447%	OK
500 kcmil	0.4128V	0.344%	0.172%	OK
750 kcmil	0.2736V	0.228%	0.114%	OK

Related Calculations

cable Wire size: 80A, 100ft bolt Watts to amps calculator functions Voltage drop formula

Frequently Asked Questions

What is the voltage drop for 6 AWG at 80A and 100ft?expand_more

6 AWG carrying 80A over 100ft has a 7.86V drop (6.55% on 120V), but 6 AWG is NEC-capped at 65A branch-circuit OCP per NEC 240.4(D), so 80A on 6 AWG is ampacity-invalid and the drop figure above is a reference calculation only, not an install spec. Reference: 3.27% 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 3.27% on 240V versus 6.55% on 120V.

Does 6 AWG meet the 3% drop target at 80A and 100ft on 120V?expand_more

On 120V, this run sits at 6.55%, which is past both 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. However, 6 AWG is ampacity-invalid for 80A (NEC 240.4(D) caps 6 AWG at 65A branch-circuit OCP), so this is a reference drop calculation only and the 3% check does not make this a valid install.

What wire gauge should I use instead of 6 AWG for this run?expand_more

This run is at 6.55% on 120V, past the 3% branch-circuit drop target. If you want to land under 3% at 80A over 100ft on 120V, the smallest gauge in our table that clears it is 2 AWG at 2.59%. Going up one size from 6 AWG is not always enough, each AWG step only drops the resistance by roughly 20-25%, so on long runs or high currents you often have to skip one or two sizes to meet the target. NEC 210.19(A) Informational Note 4 frames 3% as a recommendation, not a code requirement, so the right answer for you also depends on the load (motor startup, sensitive electronics) and how much drop is tolerable.

How do I reduce voltage drop?expand_more

Use a larger wire gauge (lower AWG number), shorten the run, or increase the source voltage. Each option reduces the percentage drop, and higher source voltage is usually the most effective change for long runs because the drop is a smaller fraction of a larger reference.

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.