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What Size Wire for 350 Amps?

For 350 amps with the displayed 75 C termination defaults, start with 500 kcmil copper or 700 kcmil aluminum. This page is mainly a large-feeder practicality check before the 400 A service step.
Load
350 A
Distance
0 ft entered
Band
Large service / feeder
Defaults
Non-continuous, 75 C lugs, 86 F, 240 V single-phase
Conductor count
3 current-carrying

Computed Starting Point

The table uses common defaults. Change the calculator inputs for the actual installation.

MaterialComputed sizeOCPDUsable ampacityGoverning constraintDefault check
Copper500 kcmil350 A380 ATermination rated 75 CPasses defaults
Aluminum700 kcmil350 A375 ATermination rated 75 CPasses defaults
What Size Wire for 350 Amps? under common non-continuous defaults: THHN or XHHW-2 insulation, 75 C terminations, 86 F ambient, 240 V single-phase, no more than three current-carrying conductors, and 0 ft route length entered.

What 350 A ChangesAt 350 A, copper shows 380 A usable ampacity and aluminum shows 375 A under the displayed 75 C defaults. The margin is larger than 300 A, but 60 C equipment, derating, product listings, long runs, lug range, and raceway limits can still change the final design.

Run the wire size calculator

Adjacent Amp Ratings

See whether stepping one standard size up or down forces a conductor jump under the same defaults.

LoadCopper sizeCopper OCPDAluminum sizeAluminum OCPD
300 A350 kcmil300 A500 kcmil300 A
350 A (this page)500 kcmil350 A700 kcmil350 A
400 A600 kcmil400 A900 kcmil400 A
Copper and aluminum starting sizes for 350 A and the neighboring published amp pages, under the same defaults as the result above.

A plateau means neighboring amp ratings share a conductor size under these defaults. A jump means a standard breaker change often needs a larger wire; confirm with your real ambient, length and terminations.

350 A Is the Large-Feeder Practicality Check

Large service / feeder context for a 350 A circuit.

A 350 A wire-size search usually means the design is already in large service, building feeder, or light commercial territory. At this size, a single-conductor answer may be electrically valid while still pushing lug range, enclosure bending space, raceway fill, pulling tension, and material handling.

Under the displayed 75 C termination defaults, copper moves from 350 kcmil at 300 A to 500 kcmil here, and aluminum moves from 500 kcmil to 700 kcmil. The next 400 A page moves copper to 600 kcmil and aluminum to 900 kcmil, so 350 A is a real decision point before 400 A equipment.

What Changes This Answer

Checks that can change the starting conductor under the displayed defaults.

  • Do not reuse 300 A conductors

    Under these defaults, 300 A uses 350 kcmil copper and 500 kcmil aluminum. This 350 A page moves to 500 kcmil copper and 700 kcmil aluminum.

  • Compare 400 A before standardizing

    The adjacent 400 A page moves copper to 600 kcmil and aluminum to 900 kcmil under the same defaults. Do not drift to 400 A without load, equipment, and utility support.

  • Confirm lug and enclosure limits

    Equipment lug range, conductor bending space, gutter size, and raceway entry layout can decide whether the single-conductor result is buildable.

  • Treat parallel sets as a separate design

    Parallel conductors may be practical at this scale, but this page does not size parallel sets. Use matching conductors, equal lengths, listed terminations, and project-specific engineering.

  • Check 60 C and derating cases

    The displayed 500 kcmil copper and 700 kcmil aluminum results are 75 C defaults. Equipment limited to 60 C, hot ambient, bundling, or long feeders can force a different result.

350 Amp Wire Size FAQs

What size wire for 350 amps?
Under the 75 C non-continuous defaults on this page, start with 500 kcmil copper or 700 kcmil aluminum. Confirm lug range, conductor product, raceway fill, voltage drop, load calculation, and utility or AHJ requirements.
Is 350 A the same wire size as 300 A?
No under these defaults. The 300 A page shows 350 kcmil copper and 500 kcmil aluminum, while 350 A moves to 500 kcmil copper and 700 kcmil aluminum.
Should I use the 400 A page instead?
Only when the load calculation, service equipment, overcurrent device, and utility or AHJ requirements support 400 A. The adjacent 400 A page uses larger conductors.
Can I use this page as final approval for a 350 A feeder?
No. Treat it as a planning starting point only. Large feeders still need load calculation, conductor product verification, lug checks, raceway fill, grounding and bonding, voltage drop, and utility or AHJ review.