What Is the Voltage Drop for 2 AWG at 78A and 75 Feet?

2 AWG copper carrying 78 amps over 75 feet on a single-phase / DC circuit drops 2.27 volts (1.89% 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.

2 AWG, 78A, 75ft · single-phase / DC

2.27 V drop (1.89% on 120V)

On 120V circuit1.89%

On 240V circuit0.9458%

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

2 AWG

Amps

Feet

Drop @ 120V

2.27V (1.89%)

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 × 78 × 0.194) ÷ 1000 = 2.27 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: (2.27 ÷ 120) × 100 = 1.89%

On 240V: (2.27 ÷ 240) × 100 = 0.9458%

How This Estimate Changes with Run Length and Gauge

Gauge Check

2 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 2 AWG at 78A at different distances:

Distance	Drop (V)	% on 120V	% on 240V	NEC (120V)
25ft	0.7566V	0.6305%	0.3153%	OK
50ft	1.51V	1.26%	0.6305%	OK
75ft	2.27V	1.89%	0.9458%	OK
100ft	3.03V	2.52%	1.26%	OK
150ft	4.54V	3.78%	1.89%	Caution
200ft	6.05V	5.04%	2.52%	Past 5%
300ft	9.08V	7.57%	3.78%	Past 5%

Same Run, Different Wire Gauges

How does wire gauge affect voltage drop for 78A at 75 feet on 120V single-phase / DC? Only gauges whose branch-circuit OCP cap is at or above the 78A 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)
2 AWG	2.27V	1.89%	0.9458%	OK
1 AWG	1.8V	1.5%	0.7507%	OK
1/0 AWG	1.43V	1.19%	0.5947%	OK
2/0 AWG	1.13V	0.9428%	0.4714%	OK
3/0 AWG	0.8962V	0.7469%	0.3734%	OK
4/0 AWG	0.7114V	0.5928%	0.2964%	OK

Related Calculations

cable Wire size: 78A, 75ft bolt Watts to amps calculator functions Voltage drop formula

Frequently Asked Questions

What is the voltage drop for 2 AWG at 78A and 75ft?expand_more

2 AWG carrying 78A over 75ft has a 2.27V drop (1.89% on 120V). Reference: 0.9458% 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 0.9458% on 240V versus 1.89% on 120V.

What wire gauge should I use instead of 2 AWG for this run?expand_more

2 AWG already sits within the 3% branch-circuit drop target at these inputs (1.89% 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 2 AWG meet the 3% drop target at 78A and 75ft on 120V?expand_more

On 120V, this run sits at 1.89%, 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.