What Is the Voltage Drop for 3/0 AWG at 100A and 25 Feet?

3/0 AWG at 100A and 25 feet: 0.383V drop (0.3192% 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.

3/0 AWG, 100A, 25ft · single-phase / DC

0.383 V drop (0.3192% on 120V)

On 120V circuit0.3192%

On 240V circuit0.1596%

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

0.38V (0.32%)

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 × 25 × 100 × 0.0766) ÷ 1000 = 0.383 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: (0.383 ÷ 120) × 100 = 0.3192%

On 240V: (0.383 ÷ 240) × 100 = 0.1596%

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 100A at different distances:

Distance	Drop (V)	% on 120V	% on 240V	NEC (120V)
25ft	0.383V	0.3192%	0.1596%	OK
50ft	0.766V	0.6383%	0.3192%	OK
75ft	1.15V	0.9575%	0.4788%	OK
100ft	1.53V	1.28%	0.6383%	OK
150ft	2.3V	1.92%	0.9575%	OK
200ft	3.06V	2.55%	1.28%	OK
300ft	4.6V	3.83%	1.92%	Caution

Same Run, Different Wire Gauges

How does wire gauge affect voltage drop for 100A at 25 feet on 120V single-phase / DC? Only gauges whose branch-circuit OCP cap is at or above the 100A 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	0.383V	0.3192%	0.1596%	OK
4/0 AWG	0.304V	0.2533%	0.1267%	OK
250 kcmil	0.2575V	0.2146%	0.1073%	OK
300 kcmil	0.2145V	0.1788%	0.0894%	OK
350 kcmil	0.1835V	0.1529%	0.0765%	OK
500 kcmil	0.129V	0.1075%	0.0538%	OK

Related Calculations

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Frequently Asked Questions

What is the voltage drop for 3/0 AWG at 100A and 25ft?expand_more

3/0 AWG carrying 100A over 25ft has a 0.383V drop (0.3192% on 120V). Reference: 0.1596% 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 3/0 AWG meet the 3% drop target at 100A and 25ft on 120V?expand_more

On 120V, this run sits at 0.3192%, 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 (0.3192% 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.

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 0.1596% on 240V versus 0.3192% on 120V.

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.