Wire Size GuideNEC 2023 · 2026 · Updated Apr 2026

What wire size for a 100 amp circuit?

Q: What is the minimum wire size for a 100 amp circuit?

The minimum wire size is 3 AWG copper or 1 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 100 amp circuit?

Yes. 1 AWG aluminum handles 100A. 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 3 AWG copper vs aluminum comparison.

Q: How far can I run 3 AWG wire on a 100 amp circuit?

At 240V, 3 AWG copper can run approximately 147 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 100 amp circuit?

Use a 100A 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 100A circuit on a 100A breaker: Use 3 AWG copper (100A capacity) or 1 AWG aluminum (100A capacity). Common applications: 100A subpanels for detached garages, workshops, and accessory dwelling units.

Copper3 AWG

Aluminum1 AWG

Breaker100A

Voltage240V

You\'re running power to a detached garage, building out an ADU that needs its own panel, or upgrading an older home from 60A to 100A service. At 100A, you\'re past branch-circuit territory and into feeder and service-entrance wiring - the rules change and the wire gets expensive fast.

All valid wire sizes for a 100 amp circuit

A 100 amp sub panel feeder is the standard for detached garages, workshops, and ADUs. The minimum wire is 3 AWG copper or 1 AWG aluminum. Aluminum is extremely common at this size, costing roughly half the price.

Feeders to detached buildings need a separate grounding electrode per NEC 250.32(A). The neutral must be isolated at the subpanel. Use a 4-wire feeder.

Common mistake: The most common 100A mistake is bonding the neutral to ground in the subpanel. In a subpanel, the neutral bar and ground bar must be separate - only the main panel bonds them together. The second mistake: running a 3-wire feeder to a detached building. NEC 250.32 requires a 4-wire feeder (two hots, neutral, ground) plus a separate grounding electrode at the detached structure.

Any gauge with ampacity equal to or greater than 100A 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
3 AWG (minimum)	Copper	100A	147 ft	1" EMT
2 AWG	Copper	115A	185 ft	1" EMT
1 AWG	Copper	130A	234 ft	1-1/4" EMT
1/0 AWG	Copper	150A	294 ft	1-1/4" EMT
2/0 AWG	Copper	175A	370 ft	1-1/2" EMT
3/0 AWG	Copper	200A	468 ft	2" EMT
4/0 AWG	Copper	230A	588 ft	2" EMT
1 AWG (minimum)	Aluminum	100A	142 ft	1" EMT
1/0 AWG	Aluminum	120A	178 ft	1-1/4" EMT
2/0 AWG	Aluminum	135A	225 ft	1-1/4" EMT
3/0 AWG	Aluminum	155A	285 ft	1-1/2" EMT
4/0 AWG	Aluminum	180A	361 ft	2" EMT
4 AWG (310.15(B)(7))	Copper	100A	116 ft	1" EMT
2 AWG (310.15(B)(7))	Aluminum	100A	112 ft	1" 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
3 AWG	Copper	73 ft	127 ft	147 ft	294 ft
2 AWG	Copper	92 ft	160 ft	185 ft	370 ft
1 AWG	Copper	116 ft	202 ft	234 ft	468 ft
1/0 AWG	Copper	147 ft	256 ft	294 ft	588 ft
2/0 AWG	Copper	186 ft	322 ft	370 ft	750 ft
3/0 AWG	Copper	234 ft	405 ft	468 ft	937 ft
4/0 AWG	Copper	297 ft	517 ft	588 ft	1200 ft
1 AWG	Aluminum	71 ft	123 ft	142 ft	285 ft
1/0 AWG	Aluminum	89 ft	155 ft	178 ft	357 ft
2/0 AWG	Aluminum	113 ft	196 ft	225 ft	454 ft
3/0 AWG	Aluminum	142 ft	247 ft	285 ft	566 ft
4/0 AWG	Aluminum	179 ft	312 ft	361 ft	714 ft
4 AWG	Copper	58 ft	101 ft	116 ft	234 ft
2 AWG	Aluminum	56 ft	97 ft	112 ft	225 ft

Common 100A circuit projects

100A subpanel (detached garage)

Run a 4-wire feeder from the main panel to a 100A subpanel in the garage. Use 1 AWG aluminum SER cable (cheaper) or 3 AWG copper in conduit. You need two hots, a neutral, and an equipment ground. Install a grounding electrode (two ground rods 6+ feet apart) at the garage per NEC 250.32. Isolate the neutral bar from the panel enclosure - do not bond neutral to ground in the subpanel.

100A subpanel (ADU/workshop)

An ADU with a full kitchen, HVAC, and water heater typically needs 100A. Run the feeder underground in PVC conduit with individual THWN-2 conductors. Do a load calculation per NEC 220.82 to verify 100A is sufficient - an ADU with electric heat and an EV charger may need 125A. Some jurisdictions require a separate meter for ADUs.

100A service upgrade

Upgrading from 60A to 100A service means replacing the meter base, service entrance cable, main breaker panel, and grounding electrode system. The utility must disconnect and reconnect the service drop. Use 4 AWG copper or 2 AWG aluminum service entrance cable per NEC Table 310.15(B)(7). This is not a DIY project - it requires a permit, inspection, and utility coordination.

100A sub panel wire size for workshop

A workshop with a welder, table saw, and dust collector needs careful load planning. Size the feeder for peak simultaneous load, not total connected load. A 100A panel gives headroom: a 240V welder (50A), table saw (15A), and dust collector (15A) rarely all run at once. Run 1 AWG aluminum in conduit for cost savings on long runs.

Frequently asked questions

What is the minimum wire size for a 100 amp circuit?

The minimum wire size is 3 AWG copper or 1 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 100 amp circuit?

Yes. 1 AWG aluminum handles 100A. 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 3 AWG copper vs aluminum comparison.

How far can I run 3 AWG wire on a 100 amp circuit?

At 240V, 3 AWG copper can run approximately 147 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 100 amp circuit?

Use a 100A 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 100 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 3 AWG Copper circuits

🧵Wire Roll3 AWG copper, 50ftCheck prices on Amazon (paid link) ⚡100A BreakerStandard pairing for 3 AWGCheck prices on Amazon (paid link) 📏Conduit1" EMT for 3 AWG runsCheck prices on Amazon (paid link)

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Requirements vary by state. NEC edition, licensing, permits, and GFCI rules differ by jurisdiction. Check your state or pick it below for personalized info across WireRef.

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