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What Size Wire for 100 Amps at 300 Feet?

At 300 ft, the 100 A feeder defaults jump again to 2/0 AWG copper or 4/0 AWG aluminum, making this a long-route cost and constructability check rather than a simple ampacity answer.
Load
100 A
Distance
300 ft
Band
100 A feeder
Defaults
Non-continuous, 75 C lugs, 86 F, 240 V single-phase

Computed Starting Point

Ampacity and voltage drop under common defaults for this amp and distance.

MaterialComputed sizeOCPDUsable ampacityGoverning constraintDefault check
Copper2/0 AWG100 A175 AVoltage dropPasses defaults
Aluminum4/0 AWG100 A180 AVoltage dropPasses defaults
What Size Wire for 100 Amps at 300 Feet? under common non-continuous defaults: THHN or XHHW-2 insulation, 75 C terminations, 86 F ambient, 240 V single-phase and no more than three current-carrying conductors.

What 300 ft ChangesAt 300 ft, the default result is 2/0 copper or 4/0 aluminum, governed by voltage drop. The conductor is now much larger than the ampacity-only 100 A answer, so raceway size, bend space, pulling difficulty and the possibility of moving equipment become part of the sizing conversation.

Run the wire size calculatorCheck voltage drop alone

Zero-Length vs This Distance

If the distance-adjusted size is larger, voltage drop governed under these defaults.

CaseCopper sizeCopper constraintAluminum sizeAluminum constraint
Ampacity only (0 ft)3 AWGTermination rated 75 C1 AWGTermination rated 75 C
300 ft (this page)2/0 AWGVoltage drop4/0 AWGVoltage drop
Copper and aluminum sizes for 100 A with no distance entered versus 300 ft one-way.

Adjacent Distances at This Amp

Neighboring published lengths for 100 A under the same defaults.

DistanceCopper sizeAluminum sizeCopper constraint
250 ft1/0 AWG3/0 AWGVoltage drop
300 ft (this page)2/0 AWG4/0 AWGVoltage drop
400 ft3/0 AWG250 kcmilVoltage drop
100 A copper and aluminum starting sizes across neighboring distance pages.

300 ft Is a Long Route Decision

100 A feeder context for 100 A at 300 ft.

A 300 ft 100 A run is no longer a short outbuilding feeder with a little extra length. It is a long trench, driveway, detached shop, pump house or equipment-pad route where conductor size, raceway fill and equipment placement all compete with each other.

Under the defaults on this page, both materials have moved again from the 250 ft result. This is the distance where the page should help a user decide whether to keep carrying the full 100 A load or revisit where the feeder terminates.

What Changes This Long-Run Answer

Checks that matter for distance-governed sizing in this amp band.

  • Treat 300 ft as a layout checkpoint

    Before ordering 2/0 copper or 4/0 aluminum, confirm whether the panel, transformer, load center or equipment pad can move closer to reduce the full-load run.

  • Compare 250 ft and 400 ft

    The 250 ft page is one step smaller, while 400 ft moves to a different conductor class. Use the adjacent table to see which side your measured route actually falls on.

  • Verify 4/0 aluminum landing

    If aluminum is the cost path, confirm the equipment lugs, torque range, bend space and raceway fill accept 4/0 aluminum before treating the result as buyable.

  • Use actual load current when lower

    If the feeder rarely carries the full 100 A, run the calculator with the design current that will actually flow. Voltage drop follows current, not the panel label.

100 A at 300 ft FAQs

What size wire for 100 amps at 300 feet?
Under the defaults on this page, start with 2/0 AWG copper or 4/0 AWG aluminum. Voltage drop governs both results.
Is 300 ft too long for a 100 A feeder?
Not automatically, but it is long enough that conductor cost, raceway planning and equipment placement should be checked before buying material.
Is 4/0 aluminum practical for a 300 ft feeder?
Sometimes, but the conductor has to land in listed lugs and fit the raceway and bending space. Check those parts before choosing aluminum only because it is cheaper.
Can I use the 250 ft wire size for a 300 ft route?
Not under these defaults. The 250 ft page lands on 1/0 copper or 3/0 aluminum, while the 300 ft page moves to 2/0 copper or 4/0 aluminum.