Wire Size GuideNEC 2023 · 2026 · Updated Apr 2026

What wire size for a 400 amp circuit?

Q: Can I use aluminum wire for a 400 amp circuit?

Not at common residential gauges. Aluminum handles 400A. Aluminum requires anti-oxidant compound and AL-rated terminals (marked AL/CU on the device). It costs roughly 40-60% less than copper but requires a larger gauge for equivalent ampacity. See the 12 AWG copper vs aluminum comparison.

Q: How far can I run the minimum AWG wire on a 400 amp circuit?

At 240V, the minimum AWG copper can run approximately N/A feet before exceeding the 3% voltage drop recommendation. For longer distances, upsize to the next gauge. Use the voltage drop calculator for your exact scenario.

Q: What breaker size for a 400 amp circuit?

Use a 400A breaker. The breaker must match the circuit rating, not the wire ampacity. For continuous loads (like EV chargers), the breaker must be rated at 125% of the load per NEC 210.19(A)(1).

For a 400A circuit on a 400A breaker: Use N/A or N/A. Common applications: 400A service for large homes, dual-panel setups, and commercial buildings.

Copper - AWG

Aluminum - AWG

Breaker400A

Voltage240V

All valid wire sizes for a 400 amp circuit

A 400 amp service is used for large homes (especially all-electric with EV charging), dual-panel installations, and commercial buildings. This is typically provided as two 200A panels fed from a 400A meter base. Wire sizing at this amperage almost always uses parallel conductors or large kcmil aluminum.

400A is a standard breaker size per NEC 240.6(A). Service entrance conductors at 400A typically use parallel sets: two sets of 3/0 AWG copper or two sets of 250 kcmil aluminum. Utility coordination is essential for 400A service - the meter base, service entrance, and transformer capacity all need to match.

Any gauge with ampacity equal to or greater than 400A per NEC 2023 Table 310.16, after 110.14(C) termination limits are applied. Smaller gauge number means thicker wire, higher cost, but lower voltage drop.

Gauge	Material	Capacity	Max distance (3% drop)	Conduit

Maximum wire run distance

One-way distance in feet before voltage drop exceeds 3%, per NEC Chapter 9 Table 8 resistance values. If your run is longer than these distances, upsize one gauge.

Gauge	Material	120V	208V	240V	480V

Common 400A circuit projects

400A residential service
400A commercial service
dual 200A panel setup

Frequently asked questions

What is the minimum wire size for a 400 amp circuit?

Consult a licensed electrician for circuits at this amperage.

Can I use aluminum wire for a 400 amp circuit?

Not at common residential gauges. Aluminum handles 400A. Aluminum requires anti-oxidant compound and AL-rated terminals (marked AL/CU on the device). It costs roughly 40-60% less than copper but requires a larger gauge for equivalent ampacity. See the 12 AWG copper vs aluminum comparison.

How far can I run the minimum AWG wire on a 400 amp circuit?

At 240V, the minimum AWG copper can run approximately N/A feet before exceeding the 3% voltage drop recommendation. For longer distances, upsize to the next gauge. Use the voltage drop calculator for your exact scenario.

What breaker size for a 400 amp circuit?

Use a 400A breaker. The breaker must match the circuit rating, not the wire ampacity. For continuous loads (like EV chargers), the breaker must be rated at 125% of the load per NEC 210.19(A)(1).

Do I need GFCI on a 400 amp circuit?

GFCI requirements depend on location, not amperage. NEC 2023 requires GFCI in kitchens, bathrooms, garages, outdoors, basements, laundry areas, and near sinks. Check the GFCI requirements by room for your specific installation.

Common products for 12 AWG Copper circuits

🧵Wire Roll12 AWG solid copper, 500ftCheck prices on Amazon (paid link) ⚡20A BreakerStandard pairing for 12 AWGCheck prices on Amazon (paid link) 🔌GFCI OutletRequired in kitchens, baths, garagesCheck prices on Amazon (paid link) 🔧Wire Strippers12 AWG compatibleCheck prices on Amazon (paid link)

As an Amazon Associate we earn from qualifying purchases.

Requirements vary by state. NEC edition, licensing, permits, and GFCI rules differ by jurisdiction. Check your state or pick it below for personalized info across WireRef.

Important: For reference only. Not a substitute for a licensed electrician. Electrical work can cause serious injury, death, fire, or property damage if performed incorrectly. Always hire a licensed electrician for electrical work, especially for service upgrades, panel work, and 240V circuits. Values are derived from NFPA 70 (NEC) for educational purposes. Always verify against your locally adopted NEC edition and amendments - local jurisdictions may enforce stricter requirements. WireRef provides reference information only and is not responsible for work performed based on this content. NEC® is a registered trademark of the National Fire Protection Association. Free NEC access via NFPA · OSHA Electrical Safety · Terms of use.

NEC 2023 references verified April 2026