What size wire for a 30 amp 240 volt circuit?
30 A at 240 V is a common dryer, shop, or equipment circuit. Check feet before you buy 10 AWG by habit.
How to run this check
- Enter 240 V, 30 A, copper, and the one-way length.
- Keep 3% unless the equipment spec is tighter.
- If the tool sizes up, open Voltage Drop and see the percent on 10 AWG.
Why 10 AWG shows up first
10 AWG copper has a 75 °C effective planning ampacity of 30 A on this site. That clears 30 A on ampacity before you look at length.
Aluminum, 60 °C NM, or a continuous-load adder can change that first size. This page does not apply the 125% continuous-load multiplier automatically.
The long-run catch
At 180 ft one-way, 30 A, 240 V, the recommended size is 6 AWG and the governing check is voltage drop.
If you already pulled 10 AWG, do not guess. Use the voltage-drop tool on the known size and decide whether the percent is acceptable for that equipment.
Planning walk-through for 30 A, 240 V, copper, 3% target
| One-way length | Recommended size | What limited it | Voltage drop |
|---|---|---|---|
| 40 ft | 10 AWG | Ampacity | 3.0 V / 1.2% |
| 180 ft | 6 AWG | Voltage drop | 5.3 V / 2.2% |
Related
FAQ
Is 10 AWG copper the 30 A answer?
It is the common short-run starting size. Long runs, aluminum, and 60 °C terminations can force a larger size.
Is 3% required by the NEC for this circuit?
No. 3% and 5% are planning targets. The job, the equipment, and the AHJ set the real limit.
Planning reference only. Verify against the current NEC, manufacturer data, and the authority having jurisdiction. This is not engineering advice or a license substitute.