Wire Size GuideNEC 2023 · 2026 · Updated Apr 2026

What wire size for a 125 amp circuit?

Q: What is the minimum wire size for a 125 amp circuit?

The minimum wire size is 1 AWG copper or 2/0 AWG aluminum per NEC 2023 Table 310.16 with 110.14(C) termination limits applied. For long runs, you may need to upsize to account for voltage drop. See the max distance table above.

Q: Can I use aluminum wire for a 125 amp circuit?

Yes. 2/0 AWG aluminum handles 125A. Aluminum requires anti-oxidant compound and AL-rated terminals (marked AL/CU on the device). It costs roughly 40-60% less than copper but requires a larger gauge for equivalent ampacity. See the 1 AWG copper vs aluminum comparison.

Q: How far can I run 1 AWG wire on a 125 amp circuit?

At 240V, 1 AWG copper can run approximately 187 feet before exceeding the 3% voltage drop recommendation. For longer distances, upsize to the next gauge. Use the voltage drop calculator for your exact scenario.

Q: What breaker size for a 125 amp circuit?

Use a 125A breaker. The breaker must match the circuit rating, not the wire ampacity. For continuous loads (like EV chargers), the breaker must be rated at 125% of the load per NEC 210.19(A)(1).

For a 125A circuit on a 125A breaker: Use 1 AWG copper (130A capacity) or 2/0 AWG aluminum (135A capacity). Common applications: 125A subpanels for large additions, ADUs, and commercial tenant spaces.

Copper1 AWG

Aluminum2/0 AWG

Breaker125A

Voltage240V

You\'re building an ADU with a full kitchen and electric water heater, finishing a large addition that needs its own panel, or a load calculation showed your detached building needs more than 100A. The jump from 100A to 125A costs surprisingly little in wire - but the breaker and panel cost more.

All valid wire sizes for a 125 amp circuit

A 125 amp circuit is common for subpanels serving large additions, ADUs with full kitchens, or commercial tenant spaces. The minimum wire is 1 AWG copper or 2/0 AWG aluminum.

125A is a standard breaker size per NEC 240.6(A). A full load calculation per NEC 220.82 (optional method) is recommended to verify the ADU or addition load fits within 125A. Some utilities require a separate meter for loads above 100A.

Common mistake: The most common 125A mistake is assuming a 100A panel will handle the load and then running out of capacity mid-project. Do the load calculation before buying wire. An ADU with an electric range (50A), water heater (30A), HVAC (30A), and general circuits (30A) already exceeds 100A on paper. The other trap: some main panels don\'t accept a 125A breaker - check your panel\'s bus rating and available breaker sizes before committing.

Any gauge with ampacity equal to or greater than 125A per NEC 2023 Table 310.16, after 110.14(C) termination limits are applied. Smaller gauge number means thicker wire, higher cost, but lower voltage drop.

Gauge	Material	Capacity	Max distance (3% drop)	Conduit
1 AWG (minimum)	Copper	130A	187 ft	1-1/4" EMT
1/0 AWG	Copper	150A	236 ft	1-1/4" EMT
2/0 AWG	Copper	175A	297 ft	1-1/2" EMT
3/0 AWG	Copper	200A	375 ft	2" EMT
4/0 AWG	Copper	230A	476 ft	2" EMT
2/0 AWG (minimum)	Aluminum	135A	180 ft	1-1/4" EMT
3/0 AWG	Aluminum	155A	229 ft	1-1/2" EMT
4/0 AWG	Aluminum	180A	288 ft	2" EMT
2 AWG (310.15(B)(7))	Copper	125A	148 ft	1-1/4" EMT
1/0 AWG (310.15(B)(7))	Aluminum	125A	143 ft	1-1/4" EMT

Maximum wire run distance

One-way distance in feet before voltage drop exceeds 3%, per NEC Chapter 9 Table 8 resistance values. If your run is longer than these distances, upsize one gauge.

Gauge	Material	120V	208V	240V	480V
1 AWG	Copper	93 ft	162 ft	187 ft	375 ft
1/0 AWG	Copper	118 ft	204 ft	236 ft	468 ft
2/0 AWG	Copper	149 ft	258 ft	297 ft	600 ft
3/0 AWG	Copper	187 ft	326 ft	375 ft	750 ft
4/0 AWG	Copper	236 ft	410 ft	476 ft	937 ft
2/0 AWG	Aluminum	90 ft	157 ft	180 ft	361 ft
3/0 AWG	Aluminum	114 ft	198 ft	229 ft	454 ft
4/0 AWG	Aluminum	144 ft	250 ft	288 ft	576 ft
2 AWG	Copper	74 ft	128 ft	148 ft	297 ft
1/0 AWG	Aluminum	71 ft	123 ft	143 ft	285 ft

Common 125A circuit projects

125A subpanel

A 125A subpanel serves large additions or buildings that exceed 100A but don\'t need a full 200A service. Run 2/0 AWG aluminum (cheapest option) or 1 AWG copper in conduit. For underground runs, use PVC Schedule 40 conduit with THWN-2 conductors. The subpanel needs its own grounding electrode if it\'s in a separate structure per NEC 250.32.

large ADU feeder

An ADU with electric cooking, electric water heater, and a mini-split needs 125A. Run the load calculation per NEC 220.82 to confirm. Use 2/0 aluminum in 1-1/4 inch PVC conduit for underground runs. If the main panel can\'t support the additional 125A load, you may need a 200A service upgrade first - check the main panel\'s available capacity.

commercial tenant panel

A commercial tenant space (salon, small restaurant, retail) often needs 125A for lighting, HVAC, and specialized equipment. The feeder runs from the building\'s main distribution panel to the tenant panel. Use aluminum conductors to save cost on long commercial runs. The tenant panel must have a main breaker for disconnect per NEC 408.36.

Frequently asked questions

What is the minimum wire size for a 125 amp circuit?

The minimum wire size is 1 AWG copper or 2/0 AWG aluminum per NEC 2023 Table 310.16 with 110.14(C) termination limits applied. For long runs, you may need to upsize to account for voltage drop. See the max distance table above.

Can I use aluminum wire for a 125 amp circuit?

Yes. 2/0 AWG aluminum handles 125A. Aluminum requires anti-oxidant compound and AL-rated terminals (marked AL/CU on the device). It costs roughly 40-60% less than copper but requires a larger gauge for equivalent ampacity. See the 1 AWG copper vs aluminum comparison.

How far can I run 1 AWG wire on a 125 amp circuit?

At 240V, 1 AWG copper can run approximately 187 feet before exceeding the 3% voltage drop recommendation. For longer distances, upsize to the next gauge. Use the voltage drop calculator for your exact scenario.

What breaker size for a 125 amp circuit?

Use a 125A breaker. The breaker must match the circuit rating, not the wire ampacity. For continuous loads (like EV chargers), the breaker must be rated at 125% of the load per NEC 210.19(A)(1).

Do I need GFCI on a 125 amp circuit?

GFCI requirements depend on location, not amperage. NEC 2023 requires GFCI in kitchens, bathrooms, garages, outdoors, basements, laundry areas, and near sinks. Check the GFCI requirements by room for your specific installation.

Common products for 1 AWG Copper circuits

🧵Wire1 AWG stranded copperCheck prices on Amazon (paid link) 📏Conduit1-1/4" EMT for 1 AWG runsCheck prices on Amazon (paid link) ⚡150A SubpanelFor 1 AWG feeder circuitsCheck prices on Amazon (paid link)

As an Amazon Associate we earn from qualifying purchases.

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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 April 2026