What wire size for a 300 amp circuit?
300A 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: 300A commercial feeders and large building services.
CopperParallel
AluminumParallel
Breaker300A
Voltage240V
Parallel conductors required
A 300 amp feeder is typical for commercial buildings. Wire sizing at 300A almost always uses parallel conductors or large kcmil aluminum. The minimum single conductor is 350 kcmil copper or 500 kcmil aluminum.
300A is a standard breaker size. Parallel conductors are standard practice: two sets of 1/0 AWG copper provide approximately 300A capacity. Each parallel set must be the same length, material, and insulation per 310.10(H).
300A 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.
NEC 2023 references verified May 2026