What size wire do I need for a 35 amp breaker?

8 AWG copper is the smallest conductor our model estimates at or above 35 A using a 75 °C insulation rating; 8 AWG is required if the terminations are limited to 60 °C. In aluminium the equivalent is 6 AWG. Verify against the code edition adopted locally before installing.

Can I use aluminium wire on a 35 amp circuit?

Yes, where the terminations are rated for aluminium. Because aluminium carries roughly 78% of the current of the same copper size, a 35 A circuit steps up to 6 AWG and uses K = 21.2 in the voltage-drop formula instead of 12.9.

How far can a 35 amp circuit run?

On 8 AWG copper the 3% voltage-drop guideline is reached near 65 ft one-way at 120 V and 131 ft at 240 V. Longer runs need the next size or two up — length, not ampacity, decides most feeder sizes.

Is a 35 amp breaker sized at 100% of the load?

Only for non-continuous loads. A continuous load is designed at 125%, so 35 A of continuous current becomes 43.8 A of design current and lands on a 45 A device with conductors sized to match.

What is typically on a 35 amp circuit?

Commonly compressor and pump circuits, small subpanels. The load type also drives the receptacle and disconnect ratings, not just the conductor size.

What Size Wire for a 35 Amp Breaker?

Conductor size, aluminium equivalent, derating and maximum run length for a 35 amp circuit — all derived from published conductor geometry and the voltage-drop formula.

Quick answer

A 35 amp circuit needs 8 AWG copper with 75 °C terminations, or 6 AWG aluminium. 8 AWG copper applies where equipment terminals are limited to 60 °C. Voltage drop reaches 3% at roughly 131 ft one-way on 240 V and 65 ft on 120 V.

Formula estimate

Copper @ 75 °C

8 AWG

Copper @ 60 °C

8 AWG

Aluminium @ 75 °C

6 AWG

3% drop @ 240 V

131ft

Conductor options for 35 A

Estimated ampacity of each candidate size, so you can see the margin you are buying.

Material / rating	Minimum size	Estimated ampacity	Margin over 35 A
Copper, 60 °C	8 AWG	37 A	+2 A
Copper, 75 °C	8 AWG	44 A	+9 A
Copper, 90 °C	10 AWG	37 A	+2 A
Aluminium, 75 °C	6 AWG	46 A	+11 A
Aluminium, 90 °C	8 AWG	39 A	+4 A

Ampacity estimated as I = 0.0670 × cmil^0.6505, scaled for insulation rating and material.

Source & method: Conductor areas come from the ASTM B258 relationship d = 5 × 92^((36 − n) / 39). Ampacity is a fitted physical model, not a reproduction of any code table, and runs within roughly ±8% of published values.

Maximum run length on 8 AWG copper

One-way distance before voltage drop passes the 3% and 5% guidelines.

System	3% limit	5% limit	Drop @ 100 ft
120 V 1Ø	65 ft	109 ft	4.56%
240 V 1Ø	131 ft	219 ft	2.28%
208 V 3Ø	131 ft	219 ft	2.28%
480 V 3Ø	304 ft	506 ft	0.99%

Source & method: VD = 2 × K × I × L / cmil single phase, 1.732 × K × I × L / cmil three phase, with K = 12.9 for copper. 8 AWG is 16,510 circular mils and 0.6282 Ω per 1000 ft at 20 °C.

Wire size by run length for 35 A

Ampacity sets the floor; distance is what actually forces the upsize on long runs. Smallest copper conductor that carries the load and still holds 3% drop.

One-way run	120 V 1Ø	240 V 1Ø	480 V 3Ø
50 ft	8 AWG	8 AWG	8 AWG
75 ft	6 AWG	8 AWG	8 AWG
100 ft	6 AWG	8 AWG	8 AWG
150 ft	4 AWG	6 AWG	8 AWG
200 ft	3 AWG	6 AWG	8 AWG
250 ft	2 AWG	4 AWG	8 AWG
300 ft	1 AWG	4 AWG	8 AWG

Sized on both criteria at once: estimated 75 C ampacity and 3% voltage drop at the stated one-way distance.

Source & method: A dash means no listed size holds 3% at that distance and voltage — split the load, raise the system voltage, or move the panel closer.

Hot attics, conduit runs and bundling

What a 35 A circuit actually needs once ambient temperature and conductor count are applied.

Ambient	3 conductors	4–6 conductors	7–9 conductors
30 °C	8 AWG	8 AWG	6 AWG
40 °C	8 AWG	6 AWG	6 AWG
50 °C	6 AWG	6 AWG	4 AWG
60 °C	4 AWG	4 AWG	3 AWG

Source & method: Ambient correction F = √((Tc − Ta) / (Tc − 30)) with Tc = 75 °C; bundling adjustment uses the standard stepped schedule (1.00 / 0.80 / 0.70). The conductor shown is the smallest copper size whose corrected ampacity still carries 35 A.

Where 35 A circuits are actually used

35 A is almost entirely an equipment-driven rating: heat pumps, compressor-driven condensers, small commercial rooftop units and motor loads whose nameplate MOCP lands between the 30 A and 40 A standard devices. It is not a size anyone chooses for a general branch circuit.

Because the load is nearly always a motor, the conductor is sized on minimum circuit ampacity while the breaker is chosen to survive locked-rotor inrush. Motor and A/C equipment circuits are one of the recognised cases where the overcurrent device may exceed the conductor's ampacity, and it is why substituting an ordinary 40 A breaker for a nameplate-specified 35 A maximum is a code violation rather than a safe upgrade.

Ambient temperature is the quiet factor at 35 A, because the load is usually a condenser sitting in full sun or a rooftop unit whose conductors run through a hot chase. Correcting ampacity for an attic or rooftop ambient routinely moves the conductor a size up, even though the breaker stays at the nameplate maximum.

Continuous loads

A continuous load — one expected to run three hours or more, like commercial lighting or an EV charger — is designed at 125% of the load current. 35 A continuous becomes 43.8 A of design current, which lands on a 45 A overcurrent device and 8 AWG copper.

Frequently asked

What size wire do I need for a 35 amp breaker?: 8 AWG copper is the smallest conductor our model estimates at or above 35 A using a 75 °C insulation rating; 8 AWG is required if the terminations are limited to 60 °C. In aluminium the equivalent is 6 AWG. Verify against the code edition adopted locally before installing.
Can I use aluminium wire on a 35 amp circuit?: Yes, where the terminations are rated for aluminium. Because aluminium carries roughly 78% of the current of the same copper size, a 35 A circuit steps up to 6 AWG and uses K = 21.2 in the voltage-drop formula instead of 12.9.
How far can a 35 amp circuit run?: On 8 AWG copper the 3% voltage-drop guideline is reached near 65 ft one-way at 120 V and 131 ft at 240 V. Longer runs need the next size or two up — length, not ampacity, decides most feeder sizes.
Is a 35 amp breaker sized at 100% of the load?: Only for non-continuous loads. A continuous load is designed at 125%, so 35 A of continuous current becomes 43.8 A of design current and lands on a 45 A device with conductors sized to match.
What is typically on a 35 amp circuit?: Commonly compressor and pump circuits, small subpanels. The load type also drives the receptacle and disconnect ratings, not just the conductor size.