What Is the Voltage Drop for 8 AWG at 7A and 125 Feet?

8 AWG copper carrying 7 amps over 125 feet on a single-phase / DC circuit drops 1.36 volts (1.13% 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.

8 AWG, 7A, 125ft · single-phase / DC

1.36 V drop (1.13% on 120V)

On 120V circuit1.13%

On 240V circuit0.5673%

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

8 AWG

Amps

Feet

Drop @ 120V

1.36V (1.13%)

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 × 7 × 0.778) ÷ 1000 = 1.36 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: (1.36 ÷ 120) × 100 = 1.13%

On 240V: (1.36 ÷ 240) × 100 = 0.5673%

How This Estimate Changes with Run Length and Gauge

Gauge Check

8 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 8 AWG at 7A at different distances:

Distance	Drop (V)	% on 120V	% on 240V	NEC (120V)
25ft	0.2723V	0.2269%	0.1135%	OK
50ft	0.5446V	0.4538%	0.2269%	OK
75ft	0.8169V	0.6808%	0.3404%	OK
100ft	1.09V	0.9077%	0.4538%	OK
150ft	1.63V	1.36%	0.6808%	OK
200ft	2.18V	1.82%	0.9077%	OK
300ft	3.27V	2.72%	1.36%	OK

Same Run, Different Wire Gauges

How does wire gauge affect voltage drop for 7A at 125 feet on 120V single-phase / DC? Only gauges whose branch-circuit OCP cap is at or above the 7A 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)
8 AWG	1.36V	1.13%	0.5673%	OK
6 AWG	0.8593V	0.716%	0.358%	OK
4 AWG	0.539V	0.4492%	0.2246%	OK
3 AWG	0.4288V	0.3573%	0.1786%	OK
2 AWG	0.3395V	0.2829%	0.1415%	OK
1 AWG	0.2695V	0.2246%	0.1123%	OK

Related Calculations

cable Wire size: 7A, 125ft bolt Watts to amps calculator functions Voltage drop formula

Frequently Asked Questions

What is the voltage drop for 8 AWG at 7A and 125ft?expand_more

8 AWG carrying 7A over 125ft has a 1.36V drop (1.13% on 120V). Reference: 0.5673% on 240V.

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 8 AWG meet the 3% drop target at 7A and 125ft on 120V?expand_more

On 120V, this run sits at 1.13%, 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.

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 0.5673% on 240V versus 1.13% on 120V.

What wire gauge should I use instead of 8 AWG for this run?expand_more

8 AWG already sits within the 3% branch-circuit drop target at these inputs (1.13% 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.