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What Size Wire for 250 Amps?

For 250 amps with the displayed 75 C termination defaults, start with 250 kcmil copper or 350 kcmil aluminum. This is the upper edge of the service / large-feeder band before the 300 A large-feeder step.
Load
250 A
Distance
0 ft entered
Band
Service / large 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
Copper250 kcmil250 A255 ATermination rated 75 CPasses defaults
Aluminum350 kcmil250 A250 ATermination rated 75 CPasses defaults
What Size Wire for 250 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 250 A ChangesAt 250 A, the displayed aluminum row lands exactly on 250 A usable ampacity under 75 C defaults, while copper shows only 255 A. Equipment limited to 60 C will force larger conductors, and product listings, bend space, raceway fill, and utility standards can change the accepted assembly.

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
225 A4/0 AWG225 A300 kcmil225 A
250 A (this page)250 kcmil250 A350 kcmil250 A
300 A350 kcmil300 A500 kcmil300 A
Copper and aluminum starting sizes for 250 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.

250 A Is the Upper Service / Feeder Step

Service / large feeder context for a 250 A circuit.

A 250 A wire-size search usually means a large dwelling feeder, shop feeder, service-equipment upgrade, or a panelboard rating above the common 200 A and 225 A choices. This is no longer a simple residential service shortcut; conductor product, lugs, raceway, and utility or AHJ requirements drive the final answer.

Under the displayed 75 C termination defaults, copper moves from 4/0 AWG at 225 A to 250 kcmil here, and aluminum moves from 300 kcmil to 350 kcmil. The next 300 A page moves copper to 350 kcmil and aluminum to 500 kcmil, so 250 A is a distinct upper-service step rather than a small tweak.

What Changes This Answer

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

  • Do not reuse 225 A conductors

    Under these defaults, 225 A uses 4/0 AWG copper and 300 kcmil aluminum. This 250 A page moves to 250 kcmil copper and 350 kcmil aluminum.

  • Watch the tight aluminum margin

    The aluminum row shows 250 A usable ampacity under the displayed 75 C defaults. Any 60 C limit, derating, product constraint, or long run can move the final size.

  • Check 60 C equipment limits

    The displayed 250 kcmil copper and 350 kcmil aluminum results are 75 C defaults. Equipment limited to 60 C will force larger conductors for a full 250 A feeder or service.

  • Plan lugs and raceway early

    At 250 A, conductor size can decide the disconnect, panel lugs, raceway trade size, bending space, and pulling plan. Confirm the equipment accepts the chosen material and size.

  • Compare 300 A before upsizing

    The adjacent 300 A page moves copper to 350 kcmil and aluminum to 500 kcmil under the same defaults. Do not change the planned rating without load and equipment support.

250 Amp Wire Size FAQs

What size wire for 250 amps?
Under the 75 C non-continuous defaults on this page, start with 250 kcmil copper or 350 kcmil aluminum. Confirm terminal ratings, conductor product, load calculation, raceway fill, voltage drop, and utility or AHJ requirements.
Is 250 A the same wire size as 225 A?
No under these defaults. The 225 A page shows 4/0 AWG copper and 300 kcmil aluminum, while 250 A moves to 250 kcmil copper and 350 kcmil aluminum.
Why does 250 A still need a service product check?
Service-entrance cable, raceway conductors, meter lugs, disconnect lugs, utility standards, and AHJ rules can use different accepted assemblies than a generic 75 C conductor-in-raceway starting point.
Can I use this page as final approval for a 250 A feeder?
No. Treat it as a planning starting point only. Large feeders still need conductor product verification, equipment lug checks, raceway fill, grounding and bonding, utility or AHJ review, and a load calculation.