What wire size do I need for 40 amps?

For a 40-amp circuit, use 8 AWG copper wire or 6 AWG aluminum wire. This is per NEC Table 310.16 at 75°C insulation temperature. Common uses: electric ranges, large air conditioners, and EV chargers.

What breaker do I need for 40 amps?

A 40-amp circuit uses a 40A double-pole circuit breaker. The breaker protects the 8 AWG copper (or 6 AWG aluminum) wire from overload. Double-pole breakers are used for 240V circuits and occupy two slots in the panel.

What wire size for an electric stove on a 40-amp circuit?

A 40-amp electric range circuit uses 8 AWG copper or 6 AWG aluminum wire on a 40A double-pole breaker. Note: most modern full-size electric ranges are now rated for 50A circuits instead.

Can a 40-amp breaker use 10 AWG wire?

No — 10 AWG copper wire is rated for 30A maximum. For a 40-amp circuit you must use at least 8 AWG copper or 6 AWG aluminum wire. Using undersized wire on an oversized breaker is a serious fire hazard.

What Wire Size for 40 Amps?

Copper Wire

8 AWG

3.2636 mm · 8.3656 mm²

Aluminum Wire

6 AWG

4.1154 mm · 13.3018 mm²

Breaker: 40A · Based on NEC Table 310.16 (75°C insulation)

Common Uses for 40A Circuits

Electric ranges, large AC units

8 AWG Copper — Key Specs

Diameter	3.2636 mm (0.12849")
Area	8.3656 mm²
Resistance at 20°C	2.0608 Ω/km
Weight	74.955 kg/km
Ampacity (75°C)	50 A

Important: For long wire runs, you may need to upsize the wire to compensate for voltage drop. NEC recommends keeping voltage drop under 3% for branch circuits. Use our voltage drop calculator to check.

Voltage Drop by Distance — 8 AWG Copper at 40A

One-way run	Drop	% of 240V	Verdict
25 ft	1.26 V	0.5%	Within the 3% branch-circuit target
50 ft	2.51 V	1.0%	Within the 3% branch-circuit target
75 ft	3.77 V	1.6%	Within the 3% branch-circuit target
100 ft	5.02 V	2.1%	Within the 3% branch-circuit target
150 ft	7.54 V	3.1%	Over 3% — upsize one gauge
200 ft	10.05 V	4.2%	Over 3% — upsize one gauge

Single-phase, 240V, full 40A load, 0.6281 Ω/1000 ft DC resistance (NEC Chapter 9, Table 8) at 75°C terminations. NEC 210.19(A) Informational Note recommends keeping branch-circuit drop at or below 3%, and 5% total across feeder plus branch circuit. Voltage drop is a performance recommendation, not a code requirement — but exceeding it causes dim lights, slow motor starts, and wasted energy.

Related Appliance Guides

Electric Range / Stove

50A double-pole · 6 AWG

Hot Tub / Spa

50A double-pole GFCI · 6 AWG

EV Charger (Level 2)

50A double-pole · 6 AWG

Welder

50A double-pole · 6 AWG

Wire types and insulation ratings → 40 amp breaker — wire, ground and load → NEC Table 250.122 — ground wire size → 8 AWG full specifications → Full AWG chart → Wire size calculator → Ampacity tables →