Wire Size GuideNEC 2023 · 2026 · Updated Apr 2026

What wire size for a 70 amp circuit?

Q: What is the minimum wire size for a 70 amp circuit?

The minimum wire size is 4 AWG copper or 3 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 70 amp circuit?

Yes. 3 AWG aluminum handles 70A. 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 4 AWG copper vs aluminum comparison.

Q: How far can I run 4 AWG wire on a 70 amp circuit?

At 240V, 4 AWG copper can run approximately 166 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 70 amp circuit?

Use a 70A 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 70A circuit on a 70A breaker: Use 4 AWG copper (85A capacity) or 3 AWG aluminum (75A capacity). Common applications: large subpanels, whole-house tankless water heaters, and heavy workshop equipment.

Copper4 AWG

Aluminum3 AWG

Breaker70A

Voltage240V

All valid wire sizes for a 70 amp circuit

A 70 amp circuit is typically used for subpanels serving workshops or additions. The minimum wire is 4 AWG copper or 3 AWG aluminum.

Large tankless electric water heaters (24-29kW) may require two or three separate 40A circuits rather than a single 70A circuit. Always check the manufacturer specifications. The 70A breaker is a standard size per NEC 240.6(A).

Any gauge with ampacity equal to or greater than 70A 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
4 AWG (minimum)	Copper	85A	166 ft	1" EMT
3 AWG	Copper	100A	209 ft	1" EMT
2 AWG	Copper	115A	265 ft	1" EMT
1 AWG	Copper	130A	333 ft	1-1/4" EMT
1/0 AWG	Copper	150A	422 ft	1-1/4" EMT
2/0 AWG	Copper	175A	535 ft	1-1/2" EMT
3/0 AWG	Copper	200A	666 ft	2" EMT
4/0 AWG	Copper	230A	857 ft	2" EMT
3 AWG (minimum)	Aluminum	75A	127 ft	1" EMT
2 AWG	Aluminum	90A	161 ft	1" EMT
1 AWG	Aluminum	100A	202 ft	1" EMT
1/0 AWG	Aluminum	120A	256 ft	1-1/4" EMT
2/0 AWG	Aluminum	135A	322 ft	1-1/4" EMT
3/0 AWG	Aluminum	155A	410 ft	1-1/2" EMT
4/0 AWG	Aluminum	180A	517 ft	2" 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
4 AWG	Copper	83 ft	144 ft	166 ft	333 ft
3 AWG	Copper	104 ft	181 ft	209 ft	422 ft
2 AWG	Copper	132 ft	229 ft	265 ft	526 ft
1 AWG	Copper	166 ft	288 ft	333 ft	666 ft
1/0 AWG	Copper	211 ft	365 ft	422 ft	833 ft
2/0 AWG	Copper	265 ft	461 ft	535 ft	1071 ft
3/0 AWG	Copper	337 ft	576 ft	666 ft	1363 ft
4/0 AWG	Copper	422 ft	731 ft	857 ft	1666 ft
3 AWG	Aluminum	63 ft	110 ft	127 ft	254 ft
2 AWG	Aluminum	80 ft	139 ft	161 ft	322 ft
1 AWG	Aluminum	101 ft	176 ft	202 ft	405 ft
1/0 AWG	Aluminum	127 ft	222 ft	256 ft	508 ft
2/0 AWG	Aluminum	162 ft	280 ft	322 ft	652 ft
3/0 AWG	Aluminum	204 ft	352 ft	410 ft	810 ft
4/0 AWG	Aluminum	256 ft	447 ft	517 ft	1034 ft

Common 70A circuit projects

70A subpanel
large tankless water heater (29kW)
heavy workshop feeder

Frequently asked questions

What is the minimum wire size for a 70 amp circuit?

The minimum wire size is 4 AWG copper or 3 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 70 amp circuit?

Yes. 3 AWG aluminum handles 70A. 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 4 AWG copper vs aluminum comparison.

How far can I run 4 AWG wire on a 70 amp circuit?

At 240V, 4 AWG copper can run approximately 166 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 70 amp circuit?

Use a 70A 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 70 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 4 AWG Copper circuits

🧵Wire Roll4 AWG copper, 100ftCheck prices on Amazon (paid link) ⚡100A SubpanelCommon load center for 4 AWG feedsCheck prices on Amazon (paid link) 📏Aluminum SER4 AWG aluminum feeder cableCheck prices on Amazon (paid link)

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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