What Size Wire for 80 Amp Breaker: Copper and Aluminum
What size wire for 80 amp breaker? The short answer is 4 AWG copper, or 2 AWG aluminum, read off the 75C column of the standard ampacity table. That one line covers most of the 80 amp subpanel feeders I wire. Everything past this point is about the exceptions, because heat, long runs, and continuous loads all push you toward a thicker conductor.
Last updated: August 13, 2026. I rebuilt this around the NEC 80 percent rule, added a full copper and aluminum size chart, corrected the old gauge numbers, and wrote a proper FAQ.
What Size Wire for 80 Amp Breaker?
Wire is rated by how much current it can carry without cooking its own insulation. That rating is called ampacity. A breaker protects the wire, not the reverse. So the conductor has to be at least as tough as the breaker feeding it. The clean answer to what size wire for 80 amp breaker is 4 AWG copper at 75C. On aluminum, step up to 2 AWG, because aluminum moves less current for the same gauge.
Here is the chart I keep taped to the bench. Copper figures are the 75C column for THHN or THWN insulation, the wire you will actually find at the counter.
| Breaker Size | Copper (75C) | Aluminum (75C) |
|---|---|---|
| 20 amps | 12 AWG | 10 AWG |
| 30 amps | 10 AWG | 8 AWG |
| 40 amps | 8 AWG | 6 AWG |
| 50 amps | 6 AWG | 4 AWG |
| 60 amps | 6 AWG | 4 AWG |
| 70 amps | 4 AWG | 3 AWG |
| 80 amps | 4 AWG | 2 AWG |
| 90 amps | 3 AWG | 2 AWG |
| 100 amps | 3 AWG | 1 AWG |
Numbers matter here. Read the row, not your gut. If your project is smaller, I ran the same logic for the wire size for a 15 amp circuit, and the method is identical.
Copper vs Aluminum for an 80 Amp Breaker
Given a free choice, I run copper. It carries more current per gauge. It terminates clean. It does not creep out from under a lug the way aluminum can once the metal warms and cools a few thousand times. Copper wins on reliability.
Aluminum wins on price, and on a long feeder that gap is real money. If you go aluminum, do three things. Size up one full step. Brush anti-oxidant paste on every termination. Torque the lugs to the number stamped on the breaker. Do that and aluminum is safe for decades. Skip it and you have built yourself a slow, hot fire.
How I Size the Wire on the Bench
Here is exactly how I do it when I am handed a load and told to feed it. Five steps, no guessing.
- Add up the continuous load in amps, the stuff that runs flat out.
- Multiply by 125 percent for anything drawing for 3 hours or more. This is the NEC 80 percent rule, worked backward.
- Round up to the next standard breaker size.
- Read the wire gauge off the 75C column for your metal.
- Check the run length. Add a gauge if voltage drop crosses 3 percent.
Worked example. Say the real load is 64 amps, continuous. Multiply by 1.25 and you land on 80 amps. The next standard breaker is 80. Copper conductor: 4 AWG. If that run stretches 120 ft to a detached shop, I bump to 3 AWG to hold the drop down. Short run in the same room? 4 AWG is fine. The rule I live by is simple: “size the wire to the breaker, then bump up for heat and distance.”
What Changes the Gauge
A handful of factors push the wire size around, and every one of them can cost you a size:
- Conductor metal, copper or aluminum.
- Insulation temperature column, 60, 75, or 90C.
- Ambient heat, plus how many current-carrying wires share the conduit.
- Continuous load versus a load that cycles on and off.
- Run length and the voltage drop that distance creates.
Voltage Drop and Long Runs
Distance quietly eats your voltage. On a short feeder inside a garage, 4 AWG copper is plenty for an 80 amp breaker. Push that same wire 150 ft out to a detached shop and the drop can slide past the 3 percent most inspectors want. That is why what size wire for 80 amp breaker is really two questions: what gauge, and how far. The fix is boring and it works. Go up a size, sometimes two. I have pulled 2 AWG copper on an 80 amp run just to keep the far end healthy. If you are also fighting a voltage mismatch on the load side, I walk through wiring a 220V heater onto a 110V supply in a separate piece.
What Happens If You Use the Wrong Gauge
Too small is the dangerous mistake. Undersized wire runs hot. Hot wire bakes its insulation brittle. Brittle insulation cracks, arcs, and starts fires inside walls where nobody sees it until smoke does. The breaker will not save you, because it is sized for the load, not for your thin wire. Thicker wire has less resistance per foot, a property tied directly to its cross-sectional area. Bigger metal, cooler run, safer circuit. Going oversized wastes money and makes the wire a pain to bend, but it never starts a fire. When in doubt, go bigger.
Frequently Asked Questions
What size wire for 80 amp breaker feeding a subpanel?
Run 4 AWG copper or 2 AWG aluminum at the 75C column. For a long feeder, or a truly continuous load, size up one gauge before you pull it.
Can I use aluminum wire for an 80 amp breaker?
Yes. Use 2 AWG aluminum, one full size larger than the copper answer. Add anti-oxidant paste and torque the lugs to spec, or the connection heats up over time.
Is 6 gauge wire enough for 80 amps?
No. Do not use 6 AWG on an 80 amp breaker. In copper it tops out near 65 amps at 75C, so it runs hot and trips or melts long before 80.
Does wire length change the gauge I need?
It can. Past roughly 100 ft, voltage drop starts to bite. Add a gauge to keep the drop under 3 percent so the far end still sees full voltage.
What happens if the wire is too small for the breaker?
The wire overheats before the breaker trips. That is how walls catch fire. Match the conductor to the breaker every time, and round up when heat or distance is a factor.
Related Reading
Bottom Line
So, what size wire for 80 amp breaker? 4 AWG copper or 2 AWG aluminum at 75C, then bump up a gauge for a long run, high ambient heat, or a continuous load. Copper is my default for reliability. Aluminum is fine if you size it up and torque the lugs. Read the chart, check the distance, and when you are unsure, go one size bigger.
