Wire sizing guide

What Size Wire for 50 Amp?

Short answer: 6 AWG copper or 4 AWG aluminum for most 50 amp circuits. Below, we break down when that baseline applies, when you need to go larger, and how to verify with a voltage drop check.

Run a voltage drop check View ampacity table
The baseline

Standard wire size for 50 amps

Per NEC Table 310.16, a 50 amp circuit requires a conductor rated for at least 50 amps of continuous current. For copper conductors with common THHN or THWN insulation rated at 75°C, that means 6 AWG. For aluminum conductors at the same temperature rating, you need 4 AWG.

These ratings assume no more than three current-carrying conductors in a raceway, an ambient temperature of 30°C (86°F), and standard installation conditions. If your installation deviates — more conductors bundled together, higher ambient temperatures, or continuous loading — derating factors apply and you may need to step up.

Common applications

Where 50 amp circuits show up

50 amp circuits are among the most frequently sized in residential and light commercial work:

  • Electric ranges and cooktops — most full-size ranges require a dedicated 50 amp, 240V circuit with 6/3 NM-B cable or individual THHN conductors in conduit.
  • Sub-panels — a 50 amp feeder to a detached garage or workshop is a common setup. These runs are often long enough to make voltage drop the controlling factor rather than ampacity alone.
  • EV chargers (Level 2) — many Level 2 EVSE units draw 40 amps continuous on a 50 amp breaker. The 80% continuous load rule means the breaker must be rated at 125% of the continuous draw, which maps to a 50 amp breaker for a 40 amp charger.
  • Welders and shop equipment — larger shop tools often specify a 50 amp supply circuit.
Copper vs. aluminum

Material comparison at 50 amps

Aluminum is lighter and cheaper per foot, but its lower conductivity means you need a larger gauge to carry the same current. For 50 amps:

  • Copper: 6 AWG — cross-section of 13.3 mm², resistance ~0.491 Ω per 1000 ft.
  • Aluminum: 4 AWG — cross-section of 21.2 mm², resistance ~0.508 Ω per 1000 ft. Despite being two gauge sizes larger, the per-foot resistance is comparable because aluminum's resistivity is about 1.6× that of copper.

For sub-panel feeders running 50+ feet, aluminum can be a cost-effective choice — but only when installed with AL-rated terminals and appropriate anti-oxidant compound. Short branch circuits (ranges, dryers) typically use copper.

Compare resistance by material
Voltage drop

When to upsize beyond 6 AWG

Ampacity tables tell you the minimum safe wire size. Voltage drop tells you whether that minimum is practical for your run length. The NEC recommends keeping voltage drop under 3% for branch circuits and 5% total for feeder + branch combined.

At 50 amps with 6 AWG copper:

  • 120V source: runs over ~55 ft one-way often exceed 3%.
  • 240V source: you get roughly double the allowable distance — around 110 ft — before hitting 3%, because the percentage is calculated against a higher base voltage.

If your run exceeds these ballpark distances, step up to 4 AWG copper or 2 AWG aluminum. Use the voltage drop calculator below to check your exact scenario.

Check voltage drop for your run
Quick reference

50 amp wire sizing at a glance

Scenario Copper Aluminum Notes
Short run (< 50 ft), 240V 6 AWG 4 AWG Standard case — ampacity is the only constraint
Medium run (50–100 ft), 240V 6 AWG 4 AWG Check voltage drop — borderline at the longer end
Long run (100+ ft), 240V 4 AWG 2 AWG Voltage drop likely controls — verify with calculator
Sub-panel feeder, 150+ ft 3 or 2 AWG 1 or 1/0 AWG Account for feeder + branch combined 5% target
Assumptions

Limitations of this guide

  • Wire sizes above are based on NEC Table 310.16, 75°C column, standard conditions.
  • Ambient temperature above 30°C, conduit fill beyond three conductors, or continuous loads may require derating — consult your local code authority.
  • This guide covers general branch circuit and feeder sizing. It does not address conduit fill calculations, grounding conductor sizing, or specific equipment manufacturer requirements.
  • Always confirm final sizing with local codes and inspection requirements.
FAQ

50 amp wire sizing questions

What size wire do I need for a 50 amp circuit?

6 AWG copper or 4 AWG aluminum for most installations, based on NEC Table 310.16 at 75°C. Longer runs may require upsizing to manage voltage drop.

Can I use 8 AWG wire for 50 amps?

No. While 8 AWG copper reaches 50A at 75°C in the table, terminal temperature limits and practical application conditions typically cap it at 40 amps. Use 6 AWG for a 50 amp circuit.

When should I upsize from 6 AWG on a 50 amp circuit?

When your one-way run length causes voltage drop to exceed 3%. At 120V, that is roughly 55 ft with copper. At 240V, you have more headroom — around 110 ft. Use the voltage drop calculator to check your specific values.

What wire size for a 50 amp 240V circuit?

The ampacity requirement is the same — 6 AWG copper or 4 AWG aluminum. The 240V source voltage gives you more distance before voltage drop becomes a concern compared to 120V circuits.