What Size Wire for a 30-Amp Breaker? 2026 NEC Guide

A 30-amp breaker requires 10 AWG copper wire or 8 AWG aluminum wire as the minimum size under the NEC. The 10 AWG limit is not just an ampacity figure, it is a hard cap set by NEC 240.4(D), which restricts 10 AWG copper to 30 amps regardless of its insulation rating. This guide walks through every common 30-amp circuit, the cable types, how far you can run the wire, and the outlets each application uses.

30-Amp Wire Size Quick Reference

Why 10 AWG Is the Minimum for 30 Amps

NEC Table 310.16 lists 10 AWG copper at 30 amps in the 60-degree column used for standard NM-B cable, and 35 amps in the 75-degree column used when equipment terminals are rated for 75 degrees. Either way, NEC 240.4(D) overrides the table and caps 10 AWG copper at 30 amps for overcurrent protection. That means you cannot put 10 AWG on a 40-amp breaker even though the 75-degree column suggests headroom. For aluminum the math is different. 10 AWG aluminum is capped at 25 amps by the same rule, so a 30-amp aluminum circuit needs 8 AWG. The takeaway is simple: 10 AWG copper or 8 AWG aluminum is the floor for any 30-amp circuit, and going smaller is both a code violation and a fire risk because the wire reaches its temperature limit before the breaker ever trips.

Common 30-Amp Circuits and Their Cable

The electric clothes dryer is the most common 30-amp circuit in a home. It uses a 30-amp double-pole breaker, 10/3 NM-B cable, and a NEMA 14-30R four-prong outlet that supplies two hot legs for 240 volts plus a neutral for the 120-volt drum motor and controls. Homes wired before 1996 often have the older three-prong NEMA 10-30R, which is grandfathered but cannot be used for new work. Electric water heaters are typically hardwired on a 30-amp circuit using 10/2 NM-B, since a water heater needs only 240 volts with no neutral. A 30-amp RV pedestal uses the NEMA TT-30R, which is a 120-volt 30-amp receptacle wired with 10/3. Other 30-amp loads include central air-conditioning condensers, some electric ranges in smaller apartments, and 30-amp sub-panels feeding a garage or shed.

Voltage Drop and How Far You Can Run 10 AWG

Ampacity sets the minimum wire size, but distance can force you larger. The NEC recommends keeping voltage drop under 3 percent on a branch circuit. For 10 AWG copper carrying 30 amps on a 240-volt circuit, the 3 percent limit is reached at roughly 75 feet. On a 120-volt circuit, such as a 30-amp RV pedestal, the same wire hits 3 percent at only about 38 feet because the lower voltage doubles the percentage drop for a given loss. If your run is longer than these figures, step up to 8 AWG copper, which extends a 240-volt 30-amp circuit to roughly 120 feet before voltage drop becomes a problem. A dryer running at reduced voltage takes longer to dry a load and wastes energy, and a well pump or compressor on an undersized long run can overheat and fail early, so the small cost of upsizing on a long pull pays for itself.

Outlets and Plugs for 30-Amp Circuits

Matching the receptacle to the load matters as much as the wire. For an electric dryer, use the NEMA 14-30R four-prong outlet on new installations. For a 240-volt-only load such as a small water heater or a 240-volt tool, the NEMA 6-30R three-prong outlet provides two hots and a ground with no neutral. For a recreational vehicle, the NEMA TT-30R is the standard 30-amp 120-volt pedestal receptacle, and it is easy to confuse with a 240-volt plug, so always confirm it is wired for 120 volts only. Never adapt a 30-amp plug onto a 50-amp circuit or vice versa without the correct dogbone adapter, because doing so either starves the appliance or exposes 30-amp wire to 50 amps of current.

Aluminum Wire on 30-Amp Circuits

Aluminum is legal for 30-amp circuits at 8 AWG, and it costs noticeably less than copper, but small-gauge aluminum branch wiring earned a bad reputation from the 1960s and 1970s when it was used at 12 and 10 AWG with incompatible devices and caused connection fires. Modern practice is to use aluminum mainly at larger feeder sizes and to keep copper for small branch circuits, though 8 AWG aluminum is acceptable when installed correctly. If you do use aluminum, apply an antioxidant compound to every termination, use only connectors and devices marked AL or CO/ALR, and torque each connection to the manufacturer specification. Loose aluminum connections expand and contract more than copper and loosen over time, which is the root cause of the historical failures.

Installation Tips and Common Mistakes

The single most common 30-amp mistake is reusing an old three-prong dryer outlet and cable on a new install instead of upgrading to the four-prong grounded configuration. Another is confusing 10/2 and 10/3 cable, a dryer needs the neutral that 10/3 provides, while a water heater does not. Always size the breaker to the wire, not the other way around, a 30-amp breaker belongs on 10 AWG, never on 12 AWG. When a 30-amp circuit feeds an outdoor location, the receptacle needs a weatherproof in-use cover and GFCI protection per NEC 210.8. Finally, remember that a 30-amp circuit serving a continuous load, one running three hours or more, should be loaded to no more than 24 amps, since the NEC requires continuous loads to be sized at 125 percent.

Electrical work carries safety and legal risk. Verify any calculation with a licensed electrician familiar with your local code amendments before performing work. This article references NEC 2023; many jurisdictions still operate under NEC 2017 or 2020 or have local amendments, so always confirm with your local AHJ.

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Data sources: NEC 2023 (NFPA 70) Table 310.16, 240.4(D), 310.12, and Article 250; NFPA 70 Handbook 2023; manufacturer termination ratings; r/electricians field reports. Written by Munir Afridi, VoltFlow editorial team.