Single-Phase AC Voltage Drop
Calculate voltage drop on a single-phase AC circuit.
Inputs
Results
This uses DC resistance only (no reactance). Fine for rough branch circuit checks.
You're at 6.6% drop. A lot of folks cap feeders at 5%. Consider bigger wire or a shorter run.
Voltage Drop
7.92 V
(6.60%)
| Voltage Drop | 7.92 V |
|---|---|
| Drop % | 6.60% % |
| Voltage at Load | 112.08 V |
· The 3% and 5% numbers are common rules of thumb, not code.
How It Works
Single-phase voltage drop uses: Voltage drop = 2 x I x R R is the one-way resistance: (ohms per 1000 ft / 1000) x length in feet. The 2 is for the round trip (hot and neutral). Resistance values here are approximate DC at 75°C.
Example
12 AWG copper, 1.98 ohms per 1000 ft, 100 ft, 20 A: voltage drop = 2 x 20 x (1.98/1000 x 100) = 7.92 V, or 6.6%.
Frequently Asked Questions
What is the acceptable voltage drop percentage?
A lot of people aim for 3% on branch circuits and 5% total for feeder and branch. That is not an NEC requirement; check your local codes and get a licensed electrician to confirm.
Why does this use DC resistance?
For branch circuit estimation, DC resistance gives a reasonable approximation. For long feeders or large conductors, AC impedance (including reactance) should be used.
These numbers are for reference only. We are not liable for any decisions you make or how you use these results in the real world. Check the current NEC and your local codes, and have a licensed electrician sign off before you install or buy. Full disclaimer