125 amp wire size

125 Amp Wire Size

A common 125 amp planning lookup is 1 AWG copper or 1/0 AWG aluminum, with final sizing controlled by installation conditions.

Inputs

Results

Immediate estimate

Common 125 amp conductor1 AWG copperLimited feeder planning lookup; verify 75C/60C terminal path and installation conditions.

Circuit or service rating125 A

MaterialCopper

Run length75 ft

Voltage dropNot estimated

Acknowledge the limitations before relying on this as a planning lookup.

Electrical sizing depends on the adopted NEC edition, terminal temperature ratings, insulation type, conductor material, conduit fill, derating, grounding, equipment labels, and local inspection requirements.

Diagram

125 amp wire lookup

A 125 amp rating and conductor material select a limited planning row.

125 A rating
Material
Run length

How this calculator works

Select conductor material and run length for a cautious 125 amp feeder planning lookup.

Lookup scope

The engine maps 125 amps to common copper and aluminum feeder planning rows.

No full design

The page does not calculate neutral load, grounding conductors, conduit fill, temperature correction, or voltage drop.

Electrical safety

Confirm equipment terminal ratings, conductor insulation, and adopted code before installing.

Lookupmatch amp rating and conductor material to a common residential planning row

Length flagflag one-way runs over 100 ft for voltage-drop review

Assumptions

Lookup scope: Limited feeder planning lookup; verify 75C/60C terminal path and installation conditions.
Not checked: Voltage drop, grounding conductor size, neutral load, service load calculation, conduit fill, ambient temperature correction, bundling, and equipment-specific requirements.

Worked examples

125 amp copper feeder

Common copper planning lookup.

1 AWG copperCommon 125 amp conductor

Long aluminum run

Shows voltage-drop caution.

1/0 AWG aluminumCommon 125 amp conductor

FAQ

Can I use this for a subpanel?

Only as early planning. Subpanel feeders also need grounding, neutral, conduit, and load checks.

Does aluminum need antioxidant?

Follow the conductor, connector, and equipment instructions for aluminum terminations.

Does this include voltage drop?

No. It only flags longer runs.

Sources and review

National Electrical Code, NFPA. Accessed 2026-07-16.
Calculators, Southwire. Accessed 2026-07-20.

Reviewed 2026-07-20. Planning estimates only; confirm project-specific requirements.