What wire size for a 40 amp circuit?
You\'re installing a cooktop separate from a wall oven, wiring a 32A EV charger like a Tesla Wall Connector, or running a circuit for a small electric range. The 40A circuit is the point where wire cost starts to matter - 8 AWG copper is noticeably more expensive than 10 AWG.
All valid wire sizes for a 40 amp circuit
A 40 amp circuit serves cooktops, small electric ranges, and 32A Level 2 EV chargers. The minimum wire is 8 AWG copper. EV chargers are continuous loads: a 32A charger requires 40A circuit (32 x 1.25).
Any gauge with ampacity equal to or greater than 40A 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 |
|---|---|---|---|---|
| 8 AWG (minimum) | Copper | 50A | 115 ft | 3/4" EMT |
| 6 AWG | Copper | 65A | 182 ft | 3/4" EMT |
| 4 AWG | Copper | 85A | 291 ft | 1" EMT |
| 3 AWG | Copper | 100A | 365 ft | 1" EMT |
| 2 AWG | Copper | 115A | 461 ft | 1" EMT |
| 1 AWG | Copper | 130A | 588 ft | 1-1/4" EMT |
| 1/0 AWG | Copper | 150A | 731 ft | 1-1/4" EMT |
| 2/0 AWG | Copper | 175A | 937 ft | 1-1/2" EMT |
| 3/0 AWG | Copper | 200A | 1153 ft | 2" EMT |
| 4/0 AWG | Copper | 230A | 1500 ft | 2" EMT |
| 8 AWG (minimum) | Aluminum | 40A | 70 ft | 3/4" EMT |
| 6 AWG | Aluminum | 50A | 111 ft | 3/4" EMT |
| 4 AWG | Aluminum | 65A | 177 ft | 3/4" EMT |
| 3 AWG | Aluminum | 75A | 223 ft | 1" EMT |
| 2 AWG | Aluminum | 90A | 283 ft | 1" EMT |
| 1 AWG | Aluminum | 100A | 357 ft | 1" EMT |
| 1/0 AWG | Aluminum | 120A | 447 ft | 1-1/4" EMT |
| 2/0 AWG | Aluminum | 135A | 566 ft | 1-1/4" EMT |
| 3/0 AWG | Aluminum | 155A | 714 ft | 1-1/2" EMT |
| 4/0 AWG | Aluminum | 180A | 909 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 |
|---|---|---|---|---|---|
| 8 AWG | Copper | 57 ft | 100 ft | 115 ft | 230 ft |
| 6 AWG | Copper | 91 ft | 158 ft | 182 ft | 365 ft |
| 4 AWG | Copper | 146 ft | 254 ft | 291 ft | 588 ft |
| 3 AWG | Copper | 184 ft | 319 ft | 365 ft | 731 ft |
| 2 AWG | Copper | 232 ft | 400 ft | 461 ft | 937 ft |
| 1 AWG | Copper | 291 ft | 508 ft | 588 ft | 1153 ft |
| 1/0 AWG | Copper | 370 ft | 638 ft | 731 ft | 1500 ft |
| 2/0 AWG | Copper | 468 ft | 810 ft | 937 ft | 1875 ft |
| 3/0 AWG | Copper | 588 ft | 1034 ft | 1153 ft | 2307 ft |
| 4/0 AWG | Copper | 731 ft | 1304 ft | 1500 ft | 3000 ft |
| 8 AWG | Aluminum | 35 ft | 60 ft | 70 ft | 140 ft |
| 6 AWG | Aluminum | 55 ft | 96 ft | 111 ft | 222 ft |
| 4 AWG | Aluminum | 88 ft | 153 ft | 177 ft | 352 ft |
| 3 AWG | Aluminum | 111 ft | 193 ft | 223 ft | 447 ft |
| 2 AWG | Aluminum | 140 ft | 243 ft | 283 ft | 566 ft |
| 1 AWG | Aluminum | 177 ft | 309 ft | 357 ft | 714 ft |
| 1/0 AWG | Aluminum | 223 ft | 389 ft | 447 ft | 882 ft |
| 2/0 AWG | Aluminum | 283 ft | 491 ft | 566 ft | 1111 ft |
| 3/0 AWG | Aluminum | 357 ft | 625 ft | 714 ft | 1428 ft |
| 4/0 AWG | Aluminum | 447 ft | 789 ft | 909 ft | 1764 ft |
Common 40A circuit projects
electric cooktop
A separate cooktop (no oven below) typically draws 30-36A and needs a 40A circuit. Run 8/3 NM-B for a hardwired connection or to a junction box behind the cooktop. Some cooktops are hardwired; others use a pigtail cord. Check the manufacturer\'s installation instructions for the exact circuit requirement - larger induction cooktops may need 50A.
Level 2 EV charger (32A)
A 32A charger like the standard Tesla Wall Connector adds about 30 miles of range per hour. Run 8/2 NM-B (or 8 AWG THHN in conduit for garage installations) to a NEMA 14-50R or hardwired connection. NEC 625.54 requires GFCI protection. Mount the charger within cord reach of the parking spot and plan the cable route to avoid vehicle traffic.
small range
Smaller electric ranges (compact or apartment-size) often specify a 40A circuit. Use 8/3 NM-B to a NEMA 14-50R receptacle - yes, a 50A receptacle on a 40A breaker is standard practice here because NEC Table 220.55 allows range demand calculations. Check the range nameplate: if it\'s over 8.75 kW, you likely need a 50A circuit instead.
Frequently asked questions
What is the minimum wire size for a 40 amp circuit?
The minimum wire size is 8 AWG copper or 8 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 40 amp circuit?
Yes. 8 AWG aluminum handles 40A. 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 8 AWG copper vs aluminum comparison.
How far can I run 8 AWG wire on a 40 amp circuit?
At 240V, 8 AWG copper can run approximately 115 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 40 amp circuit?
Use a 40A 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 40 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 8 AWG Copper circuits
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NEC 2023 references verified April 2026