What size wire do I need for a 80 amp breaker?

4 AWG copper is the smallest conductor our model estimates at or above 80 A using a 75 °C insulation rating; 2 AWG is required if the terminations are limited to 60 °C. In aluminium the equivalent is 2 AWG. Verify against the code edition adopted locally before installing.

Can I use aluminium wire on a 80 amp circuit?

Yes, where the terminations are rated for aluminium. Because aluminium carries roughly 78% of the current of the same copper size, a 80 A circuit steps up to 2 AWG and uses K = 21.2 in the voltage-drop formula instead of 12.9.

How far can a 80 amp circuit run?

On 4 AWG copper the 3% voltage-drop guideline is reached near 72 ft one-way at 120 V and 145 ft at 240 V. Longer runs need the next size or two up — length, not ampacity, decides most feeder sizes.

Is a 80 amp breaker sized at 100% of the load?

Only for non-continuous loads. A continuous load is designed at 125%, so 80 A of continuous current becomes 100 A of design current and lands on a 100 A device with conductors sized to match.

What is typically on a 80 amp circuit?

Commonly detached garage or shop feeders. The load type also drives the receptacle and disconnect ratings, not just the conductor size.

What Size Wire for a 80 Amp Breaker?

Conductor size, aluminium equivalent, derating and maximum run length for a 80 amp circuit — all derived from published conductor geometry and the voltage-drop formula.

Quick answer

A 80 amp circuit needs 4 AWG copper with 75 °C terminations, or 2 AWG aluminium. 2 AWG copper applies where equipment terminals are limited to 60 °C. Voltage drop reaches 3% at roughly 145 ft one-way on 240 V and 72 ft on 120 V.

Formula estimate

Copper @ 75 °C

4 AWG

Copper @ 60 °C

2 AWG

Aluminium @ 75 °C

2 AWG

3% drop @ 240 V

145ft

Conductor options for 80 A

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

Material / rating	Minimum size	Estimated ampacity	Margin over 80 A
Copper, 60 °C	2 AWG	92 A	+12 A
Copper, 75 °C	4 AWG	80 A	+0 A
Copper, 90 °C	4 AWG	90 A	+10 A
Aluminium, 75 °C	2 AWG	84 A	+4 A
Aluminium, 90 °C	3 AWG	82 A	+2 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 4 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	72 ft	121 ft	4.12%
240 V 1Ø	145 ft	242 ft	2.06%
208 V 3Ø	145 ft	242 ft	2.06%
480 V 3Ø	336 ft	560 ft	0.89%

Source & method: VD = 2 × K × I × L / cmil single phase, 1.732 × K × I × L / cmil three phase, with K = 12.9 for copper. 4 AWG is 41,741 circular mils and 0.2485 Ω per 1000 ft at 20 °C.

Wire size by run length for 80 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	4 AWG	4 AWG	4 AWG
75 ft	3 AWG	4 AWG	4 AWG
100 ft	2 AWG	4 AWG	4 AWG
150 ft	1/0 AWG	3 AWG	4 AWG
200 ft	2/0 AWG	2 AWG	4 AWG
250 ft	3/0 AWG	1 AWG	4 AWG
300 ft	4/0 AWG	1/0 AWG	4 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 80 A circuit actually needs once ambient temperature and conductor count are applied.

Ambient	3 conductors	4–6 conductors	7–9 conductors
30 °C	4 AWG	2 AWG	1 AWG
40 °C	3 AWG	1 AWG	1/0 AWG
50 °C	2 AWG	1/0 AWG	2/0 AWG
60 °C	1/0 AWG	3/0 AWG	3/0 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 80 A.

Where 80 A circuits are actually used

80 A covers larger dwelling subpanels, small commercial HVAC feeders, machine-tool feeds and 64 A continuous EV charging installations. It sits between two common service sizes, so it is nearly always a feeder to a distribution point rather than to a single load.

Continuous-load treatment is usually the deciding factor at this rating. An 80 A device serving a load that runs three hours or more is limited to 64 A of actual load, and commercial lighting or charging installations reach that limit routinely. The conductor must also carry the calculated load at its corrected ampacity, so ambient temperature in an attic or rooftop chase can quietly force the next size up.

Because 80 A sits between the 60 A and 100 A panel steps, the equipment tends to be lug-only distribution or a specific machine disconnect rather than a general load centre. Confirm the downstream enclosure is rated for the device size before sizing conductors, since a panel listed at 60 A cannot legally be fed by an 80 A device.

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. 80 A continuous becomes 100 A of design current, which lands on a 100 A overcurrent device and 2 AWG copper.

Frequently asked

What size wire do I need for a 80 amp breaker?: 4 AWG copper is the smallest conductor our model estimates at or above 80 A using a 75 °C insulation rating; 2 AWG is required if the terminations are limited to 60 °C. In aluminium the equivalent is 2 AWG. Verify against the code edition adopted locally before installing.
Can I use aluminium wire on a 80 amp circuit?: Yes, where the terminations are rated for aluminium. Because aluminium carries roughly 78% of the current of the same copper size, a 80 A circuit steps up to 2 AWG and uses K = 21.2 in the voltage-drop formula instead of 12.9.
How far can a 80 amp circuit run?: On 4 AWG copper the 3% voltage-drop guideline is reached near 72 ft one-way at 120 V and 145 ft at 240 V. Longer runs need the next size or two up — length, not ampacity, decides most feeder sizes.
Is a 80 amp breaker sized at 100% of the load?: Only for non-continuous loads. A continuous load is designed at 125%, so 80 A of continuous current becomes 100 A of design current and lands on a 100 A device with conductors sized to match.
What is typically on a 80 amp circuit?: Commonly detached garage or shop feeders. The load type also drives the receptacle and disconnect ratings, not just the conductor size.