Three-Phase AC Voltage Drop
Calculate voltage drop on a three-phase AC circuit.
Inputs
Results
This uses DC resistance only (no reactance). Fine for rough branch circuit checks.
You're at 4.6% drop. Many people keep branch circuits under 3%. Consider upsizing the wire.
Voltage Drop
9.66 V
(4.65%)
| Voltage Drop | 9.66 V |
|---|---|
| Drop % | 4.65% % |
| Voltage at Load | 198.34 V |
· The 3% and 5% numbers are common rules of thumb, not code.
How It Works
Three-phase voltage drop uses: Voltage drop = 1.732 x I x R (1.732 is the square root of 3.) R is one-way resistance: (ohms per 1000 ft / 1000) x length in feet. Same resistance table as single-phase; the 1.732 factor is for three-phase balanced loads.
Example
10 AWG copper, 1.24 ohms per 1000 ft, 150 ft, 30 A: voltage drop = 1.732 x 30 x (1.24/1000 x 150) = about 9.67 V, or 4.6%.
Frequently Asked Questions
Should I enter line-to-line or line-to-neutral voltage?
Enter the line-to-line voltage (e.g., 208 V, 480 V). The formula uses L-L voltage with the √3 multiplier.
Does this account for reactance?
No. This v1 uses DC resistance only. For precise large-conductor calculations, add the AC reactance component from NEC Chapter 9, Table 9.
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