What Size Wire for 30 Amps?

Quick answer: wire size for a 30 amp breaker

Minimum conductor allowed on a 30 A breaker, with not more than three current-carrying conductors at 30 °C (86 °F) ambient.

Unlike larger circuits, the terminal temperature does not change the answer here: 10 AWG copper is 30 A even in the 60 °C column, so it suits NM cable, UF cable and THHN in conduit alike. Its 75 °C and 90 °C ratings (35 A and 40 A) are only useful as a starting point for derating, because the breaker is still capped at 30 A.

The small-conductor rule: why 12 AWG and 10 AWG aluminum fail

NEC 240.4(D) sets maximum breaker sizes for small wire that override Table 310.16:

So 10 AWG copper is the smallest wire allowed on 30 A, and it is also the largest breaker 10 AWG copper can have (outside the motor, A/C and welder exceptions in 240.4(G), where the equipment nameplate sets the maximum breaker).

Wire size for a 30 amp dryer (NEMA 14-30)

NEC 220.54 counts a household electric dryer at 5,000 W or its nameplate rating, whichever is larger. A 5,000 W dryer at 240 V draws 20.8 A, and most dryers list a 30 A circuit on the nameplate. The usual wiring is:

• 10/3 NM-B with ground (two hots, neutral, ground) to a 4-wire NEMA 14-30R receptacle, on a 30 A double-pole breaker.
• The neutral is needed because the dryer's timer, motor and light run on 120 V.
• New dryer circuits must be 4-wire. A 3-wire 10-30 receptacle using the neutral as the ground may only stay on existing branch circuits (NEC 250.140 exception).

Wire size for a 30 amp water heater

NEC 422.13 treats a fixed storage water heater of 120 gallons or less as a continuous load, so the branch circuit must be at least 125% of the nameplate current. For common 240 V elements:

A water heater has no 120 V parts, so 10/2 NM-B with ground is enough. If the nameplate gives a 208 V rating or a different wattage, recalculate from the nameplate. Tankless electric heaters draw far more and often need several 40 A to 60 A circuits.

Wire size for a 24 A EV charger or a 30 amp RV hookup

EV charger: EV supply equipment is a continuous load, so NEC 625.41 sizes the breaker at 125% of the charger's setting. A charger set to 24 A needs a 30 A breaker and 10 AWG copper. A Level 2 charger on a 30 A circuit adds roughly 5.8 kW at 240 V.

RV pedestal: a 30 A RV hookup is 120 V, not 240 V. It uses a NEMA TT-30R receptacle with one hot, a neutral and a ground, wired with 10 AWG copper. Because the voltage is half, voltage drop limits the run sooner: see the 120 V column below.

Air conditioners and heat pumps: use the nameplate minimum circuit ampacity (MCA) for the wire and the maximum overcurrent protection (MOCP) for the breaker, per NEC Article 440. A unit with an MCA of 22 A and an MOCP of 30 A can use 10 AWG copper on a 30 A breaker, and some units allow 12 AWG wire with a larger breaker under 240.4(G).

Wire size for 30 amps by distance

Smallest size that keeps the run at or under a 3% voltage drop. The 24 A columns are for a continuous load on a 30 A breaker, such as an EV charger. Ampacity sets the floor, so the table never goes below 10 AWG copper or 8 AWG aluminum.

Example: a 24 A EV charger 125 ft from the panel. 10 AWG copper reaches 123 ft at 24 A, so the run needs 8 AWG copper, which reaches 196 ft. Check that the charger and breaker terminals accept the larger wire, and upsize the ground too (see ground).

Maximum length at 30 amps by wire size

The longest one-way run, in feet, before each size reaches the drop shown. Three-phase columns use the √3 formula. These are DC resistance figures.

Copper

Aluminum

Formulas: single phase L = %·V·1000 / (2·I·R), three phase L = %·V·1000 / (√3·I·R), with R in ohms per 1000 ft. The NEC informational notes in 210.19 and 215.2 recommend 3% on a branch circuit or feeder and 5% total. Use the voltage drop calculator for your exact load.

Ground wire for 30 amps

• Equipment grounding conductor: 10 AWG copper or 8 AWG aluminum, from the 30 A row of NEC Table 250.122. In 10/2 and 10/3 NM-B the bare ground is already 10 AWG.
• Upsized hots: going from 10 AWG (10,380 cmil) to 8 AWG (16,510 cmil) is a ratio of 1.59, so under 250.122(B) the 10 AWG ground must be at least 16,510 cmil, which is 8 AWG copper. In practice the ground ends up the same size as the hots.

Conduit size for 30 amp wire

Smallest conduit at 40% fill (NEC Chapter 9 Table 1) using THHN/THWN-2 areas from Chapter 9 Table 5.

XHHW-2 aluminum areas differ slightly from THHN, so check the conduit fill calculator for your insulation.

How much load can a 30 amp circuit carry?

Balanced load, unity power factor. The amps to watts calculator handles power factor.

When more than three wires share a conduit

With four to six current-carrying conductors in one raceway, NEC 310.15(C)(1) cuts ampacity to 80%. Starting from the 90 °C column, 10 AWG copper gives 32 A, still enough for 30 A. At seven to nine conductors (70%) it drops to 28 A, so upsize to 8 AWG (38 A). See wire derating.

In Canada

CEC Table 2 also rates 10 AWG copper at 30 A in the 60 °C column, and CEC Rule 14-104 limits the overcurrent protection on small conductors in the same way as NEC 240.4(D), so a 30 A circuit is 10 AWG copper in Canada too. Rule 8-102 makes the 3% and 5% voltage drop limits mandatory, and distances are in metres. See CEC Table 2 for run lengths in metres by breaker, or use the Canadian wire size calculator.

For larger circuits, see wire size for 50 amps, 60 amps, 100 amps and 200 amps.

This page is a quick reference. Confirm against the code edition your jurisdiction has adopted, the equipment markings and your inspector.