What Size Wire for a 30 Amp Breaker?

Use 10 AWG copper for a 30 amp breaker. If you use aluminum, step up to 8 AWG, because 10 AWG aluminum is limited to a 25 amp breaker.

The answer

10 AWG copper

8 AWG aluminum (75 °C terminals)

Wire size for a 30 amp breaker
Case	Wire size	Table ampacity	Area
Copper · 75 °C THHN in conduit, most modern equipment	10 AWG	35 A	5.3 mm²
Copper · 60 °C NM / Romex cable, older terminals	10 AWG	30 A	5.3 mm²
Aluminum · 75 °C Needs connectors and terminals listed for aluminum	8 AWG	40 A	8.4 mm²

Calculate for your exact distance

On this page

The answer
How the answer is worked out
Why 10 AWG copper works
Common 30 amp uses
Aluminum
How far can you run it
Before you buy wire

How the answer is worked out

The breaker is 30 A. The smallest copper wire with a 75 °C table ampacity at or above 30 A is 10 AWG, rated 35 A, with a cross-section of 5.3 mm².

For 60 °C terminals or NM cable the smallest copper size is 10 AWG, rated 30 A in the 60 °C column.

Aluminum uses its own column. The smallest aluminum size at 75 °C for this rating is 8 AWG, rated 40 A. Aluminum conductors need connectors and terminals listed for aluminum.

NEC 240.4(D) also limits the breaker for small conductors: 14 AWG copper is capped at 15 A, 12 AWG copper at 20 A, 10 AWG copper at 30 A, 12 AWG aluminum at 15 A and 10 AWG aluminum at 25 A. The sizes in the table respect those caps, so a wire is never paired with a breaker larger than its limit.

Why 10 AWG copper works

10 AWG copper is rated 30 A at the 60 °C column and 35 A at 75 °C, and NEC 240.4(D) allows it to be protected at 30 A. 12 AWG is limited to 20 A and is too small.

Common 30 amp uses

Thirty-amp circuits typically feed electric dryers, tank water heaters and 30 amp RV or trailer outlets. Check the nameplate on your appliance: the manufacturer's required circuit size always overrides a general chart.

Aluminum

10 AWG aluminum is limited to a 25 amp breaker under NEC 240.4(D), so a 30 amp breaker needs 8 AWG aluminum. Use connectors and lugs rated for aluminum.

How far can you run it? (3% voltage drop)

The distance table uses the same resistance-only model as the calculator, with a 3% limit and the wire at 75 °C. Aluminum has about 1.6 times the resistance of copper for the same size, so an aluminum run of the same length drops more voltage.

Assumes the full 30 A load on a single-phase 240 V circuit, a 75 °C conductor, copper or aluminum, a 3% voltage drop limit and the one-way length in the table. Aluminum shows a dash where that size cannot carry the full current.

Maximum one-way length for 3% drop at 30 A, 240 V, 75 °C conductor
Wire size	Copper	Aluminum
10 AWG	96.8 ft [29.5 m]	58.8 ft [17.9 m]
8 AWG	154.0 ft [46.9 m]	93.5 ft [28.5 m]
6 AWG	244.9 ft [74.6 m]	148.7 ft [45.3 m]
4 AWG	389.3 ft [118.7 m]	236.5 ft [72.1 m]

Need a specific distance? See: What Size Wire for 30 Amps at 100 Feet? , 12V Wire Size Chart: Amps vs Length

Before you buy wire

The table is a starting point. Work through this list before you order conductors, and keep the answer that matches your real installation.

Read the equipment nameplate and the breaker. A manufacturer's required circuit size overrides any general table.
Check the terminal rating on the breaker, the panel lugs and the equipment. Use the 60 °C or 75 °C column that matches the lowest rated part.
Identify the cable type. NM (Romex) cable is limited to the 60 °C column by NEC 334.80, while conductors in conduit are usually rated 75 °C or higher.
Measure the one-way distance from the panel to the load, then check voltage drop with the table or the calculator. If the run is long, go up one size.
Confirm the design with your local code, the authority having jurisdiction and a licensed electrician before you cut wire or install a breaker.

This is general information based on NEC tables, not a permit or an installation plan. Local amendments, the equipment nameplate and an inspector decide what is acceptable. Read the disclaimer.