30 Amp Wire Size — Quick Reference
Need to account for voltage drop on a longer run?
Calculate for Your Circuit Length →Why #10 AWG Copper for a 30-Amp Circuit?
Per NEC Table 310.15(B)(16), #10 AWG copper is rated for 30A at 60°C and 35A at 75°C. Most residential and commercial panels and devices use 75°C-rated terminals, so #10 AWG copper satisfies a 30A overcurrent device at standard installation conditions.
The NEC requires that conductors be protected at their ampacity. Since #10 AWG copper is rated 35A at 75°C, pairing it with a 30A breaker is code-compliant — the breaker will trip before the wire overheats.
For aluminum, #8 AWG is the minimum: #8 AWG aluminum is rated 40A at 75°C, which is the next standard size up and satisfies protection by a 30A breaker with ampacity to spare.
Common 30-Amp Circuit Applications
- Electric dryer: Standard residential dryer circuit — 240V, 30A double-pole breaker, NEMA 14-30 outlet, 4-wire required for new installs (NEC 250.140)
- Air conditioner / heat pump (smaller units): Many window or mini-split A/C units rated ≤ 30A MCA
- Welding outlet (small welder): 240V/30A NEMA 6-30 outlet for home shop welders
- RV pedestal (30A): 120V single-pole NEMA TT-30 for RV hookups
- Small subpanel feeder: 30A feeder to a small shed or workshop panel
- Electric water heater: Some smaller tankless or storage units use a 30A circuit
Voltage Drop on 30-Amp Circuits
For a 240V, 30A circuit with #10 AWG copper, the voltage drop stays within the NEC 3% recommendation for runs up to approximately 75–80 feet (one-way). Beyond that, upgrade to #8 AWG copper to keep drop under 3%.
For 120V applications at 30A (uncommon but used for RV pedestals), #10 AWG copper is limited to approximately 35–40 feet before exceeding 3% voltage drop. Use the Wire Size Calculator to verify for your specific run.
Important Note on Dryer Wiring
NEC 250.140 (amended in the 1996 NEC) requires 4-wire connections (two hots, neutral, and ground) for new dryer circuits. Older homes may have 3-wire dryer circuits (two hots and neutral, with neutral doubling as ground) — this is permitted as a grandfathered installation but not allowed for new work or when replacing a receptacle.
When roughing in a new dryer circuit, always install 4-wire cable (10/3 with ground) or 4 individual conductors in conduit and a NEMA 14-30 outlet.
Frequently Asked Questions
Per NEC Table 310.15(B)(16): #10 AWG copper (35A at 75°C) or #8 AWG aluminum (40A at 75°C) are the minimum sizes for a 30A circuit at standard installation conditions.
A 30-amp double-pole breaker for 240V circuits (dryers, A/C, welders). A 30A single-pole breaker for 120V circuits (RV outlets). Both are standard NEC 240.6(A) sizes.
No. #12 AWG copper is rated 20A at 75°C. Using it with a 30A breaker violates NEC 240.4 by allowing more current than the conductor is rated for. Minimum is #10 AWG copper for a 30A circuit.
#10 AWG copper (4-wire: two hots, neutral, ground) with a 30A double-pole breaker and NEMA 14-30 outlet. NEC 250.140 requires 4-wire for all new dryer circuits.
Approximately 75–80 feet one-way before exceeding the NEC 3% voltage drop recommendation. For longer runs, upsize to #8 AWG copper (approximately 124 feet) to stay within 3%.
For 240V circuits, yes — a double-pole breaker is required to interrupt both hot conductors. For 120V applications at 30A (such as an RV outlet), a single-pole 30A breaker is used.