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Wire Size GuideNEC 2023 · 2026 · Updated May 2026
What wire size for a 400 amp circuit?
400A circuits typically require parallel conductors or large kcmil wire sets. WireRef does not size parallel conductor assemblies on this page. Consult a licensed electrician or electrical engineer for conductor sizing, raceway fill, and termination details. Common applications: 400A service for large homes, dual-panel setups, and commercial buildings.
CopperParallel
AluminumParallel
Breaker400A
Voltage240V
Parallel conductors required
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.
400A exceeds WireRef's single-conductor sizing range. Circuits at this rating typically use parallel conductors, large kcmil conductors, or installation-specific equipment that cannot be reduced to a single wire-size answer.
Use a licensed electrician or electrical engineer to size the conductor sets, raceways, lugs, and overcurrent protection for your installation. At this amperage, the service type, conductor material, termination rating, and installation method all materially affect the answer.
WireRef's single-conductor wire-size guidance currently tops out at 225A. For higher ratings, refer to engineered drawings, manufacturer data, and your local code requirements instead of a simplified breaker-to-wire chart.
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.