What Is the Voltage Drop for 3 AWG at 37A and 100 Feet?

3 AWG at 37A and 100 feet: 1.81V drop (1.51% 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, 37A, 100ft · single-phase / DC

1.81 V drop (1.51% on 120V)

On 120V circuit1.51%

On 240V circuit0.7554%

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

1.81V (1.51%)

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 × 37 × 0.245) ÷ 1000 = 1.81 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: (1.81 ÷ 120) × 100 = 1.51%

On 240V: (1.81 ÷ 240) × 100 = 0.7554%

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 37A at different distances:

Distance	Drop (V)	% on 120V	% on 240V	NEC (120V)
25ft	0.4533V	0.3777%	0.1889%	OK
50ft	0.9065V	0.7554%	0.3777%	OK
75ft	1.36V	1.13%	0.5666%	OK
100ft	1.81V	1.51%	0.7554%	OK
150ft	2.72V	2.27%	1.13%	OK
200ft	3.63V	3.02%	1.51%	Caution
300ft	5.44V	4.53%	2.27%	Caution

Same Run, Different Wire Gauges

How does wire gauge affect voltage drop for 37A at 100 feet on 120V single-phase / DC? Only gauges whose branch-circuit OCP cap is at or above the 37A 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	1.81V	1.51%	0.7554%	OK
2 AWG	1.44V	1.2%	0.5982%	OK
1 AWG	1.14V	0.9497%	0.4748%	OK
1/0 AWG	0.9028V	0.7523%	0.3762%	OK
2/0 AWG	0.7156V	0.5963%	0.2982%	OK
3/0 AWG	0.5668V	0.4724%	0.2362%	OK

Related Calculations

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Frequently Asked Questions

What is the voltage drop for 3 AWG at 37A and 100ft?expand_more

3 AWG carrying 37A over 100ft has a 1.81V drop (1.51% on 120V). Reference: 0.7554% 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 AWG meet the 3% drop target at 37A and 100ft on 120V?expand_more

On 120V, this run sits at 1.51%, 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 0.7554% on 240V versus 1.51% 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 (1.51% 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.