30 Amp Wire Size: What Gauge Wire Do You Need?
NEC-based wire gauge for a 30 ampbreaker — copper and aluminum sizes, ground wire, conduit, and when to upsize for voltage drop.
For a 30 amp circuit, use #10 AWG copper or #8 AWG aluminum wire (THWN/THHN rated at 75°C).
Based on NEC Table 310.16 (75°C column) and, where noted, Table 310.12 for dwelling services. Confirm termination ratings and local amendments before installing.
30 Amp Wire Size at a Glance
| Copper wire size | #10 AWG |
|---|---|
| Aluminum wire size | #8 AWG |
| Breaker size | 30 amp |
| Ground wire | #10 AWG copper |
| Typical conduit | 1/2" EMT (three #10 THHN conductors) |
Verify conduit fill for your exact conductor count and insulation type with the conduit fill calculator.
Common Uses for a 30 amp Circuit
- Electric clothes dryers (30A, 240V, 4-wire circuit)
- RV outlets (TT-30, 30A 120V)
- Small electric water heaters (up to 4,500W at 240V)
- Window or small ductless air conditioners
- Welder outlets for light-duty welders
When to Upsize for Voltage Drop
For 240V runs longer than about 100 feet, upsize from #10 to #8 copper to keep voltage drop under the NEC-recommended 3%. For a 30A load at 120V (such as an RV pedestal), the threshold is closer to 50-60 feet because voltage drop is twice as significant at half the voltage.
The NEC recommends (in informational notes to 210.19 and 215.2) keeping voltage drop under 3% on a branch circuit or feeder and 5% total. Ampacity tables ignore distance entirely, so on any run much past 100 feet, check the numbers with the voltage drop calculator before buying wire.
NEC References and Code Notes
- NEC 240.4(D)(7) caps #10 AWG copper at a 30 amp overcurrent device, even though Table 310.16 lists 35A at 75°C. This is the "small conductor rule."
- #8 AWG aluminum is rated 40A at 75°C in Table 310.16, which safely covers a 30 amp breaker.
- Dryer circuits require a 4-wire feed (two hots, neutral, ground) per NEC 250.140 — 3-wire dryer circuits are only permitted in existing installations.
- The equipment grounding conductor for a 30 amp circuit is #10 AWG copper per Table 250.122.
See the NEC code reference for related articles. Always confirm requirements with your local authority having jurisdiction.
Frequently Asked Questions
Can I use 12 gauge wire on a 30 amp breaker?
No. #12 AWG copper is limited to 20 amps by NEC 240.4(D)(5). Putting it on a 30 amp breaker removes the overload protection the wire needs and creates a fire hazard. A 30 amp breaker requires at least #10 AWG copper or #8 AWG aluminum.
What size wire do I need for a 30 amp dryer circuit?
A 30 amp, 240V dryer circuit needs #10 AWG copper (typically 10/3 NM-B cable with ground) run as a 4-wire circuit: two hots, a neutral, and an equipment ground. The receptacle is a NEMA 14-30R. Older 3-wire (NEMA 10-30) setups are grandfathered but not allowed in new work per NEC 250.140.
How far can I run 10 gauge wire on a 30 amp circuit?
At 240V with a full 30A load, #10 copper stays under 3% voltage drop out to roughly 100-110 feet. At 120V, the practical limit is about 50-55 feet. Beyond those distances, upsize to #8 AWG copper. Run the numbers for your exact load with a voltage drop calculator.
Can I use 10/2 wire for a 30 amp RV outlet?
Yes, for a TT-30 (30A, 120V) RV receptacle, 10/2 NM-B with ground is correct: one hot, one neutral, one ground on a single-pole 30 amp breaker. Do not confuse it with a 14-30 dryer receptacle — wiring a TT-30 at 240V will destroy RV electronics.
Related Tools and Wire Size Guides
Wire Sizing Calculator
Calculate the exact wire gauge for any load, voltage, and distance per NEC tables.
Calculate Wire Size →Voltage Drop Calculator
Check whether your run length forces a larger conductor than ampacity alone requires.
Calculate Voltage Drop →Wire Ampacity Chart
Full NEC Table 310.16 ampacities at 60°C, 75°C, and 90°C for copper and aluminum.
View Ampacity Chart →Breaker Size Calculator
Find the right breaker for a given load, including the 125% continuous-load rule.
Size a Breaker →40 Amp Wire Size: What Gauge Wire Do You Need?
For a 40 amp circuit, use #8 AWG copper or #6 AWG aluminum wire (THWN/THHN rated at 75°C).
Read the Guide →50 Amp Wire Size: What Gauge Wire Do You Need?
For a 50 amp circuit, use #6 AWG copper or #4 AWG aluminum wire (THWN/THHN rated at 75°C).
Read the Guide →60 Amp Wire Size: What Gauge Wire Do You Need?
For a 60 amp circuit, use #6 AWG copper (rated 65A at 75°C) or #4 AWG aluminum wire.
Read the Guide →