Wire Ampacity Chart

Ampacity is the current a wire can safely carry. This chart shows copper wire at the 60°C rating common in homes, with typical uses. Aluminum carries less and must be sized up.

FAQ

Does wire ampacity change based on installation conditions? Yes. Ampacity ratings assume specific conditions like ambient temperature and number of current-carrying conductors bundled together, so wires run in hot attics or bundled with several others often need to be derated below their base ampacity rating.

See the Breaker Size Chart and AWG Wire Gauge Chart.

Why 60°C, 75°C, and 90°C Ratings Differ for the Same Wire

The same copper conductor carries different ampacity ratings depending on its insulation’s temperature rating — 60°C, 75°C, and 90°C are the three common NEC columns. A higher-rated insulation lets the same wire run hotter before it’s considered at its limit, so the ampacity number jumps between columns even though the copper itself hasn’t changed; what’s changed is how much heat the insulation can tolerate before degrading.

The Terminal, Not Just the Wire, Can Be the Real Limit

Even a wire insulated for 90°C often gets de-rated back down to its 60°C ampacity in practice, because most circuit breakers and devices are only rated for connection at 60°C or 75°C terminals. The wire’s own temperature rating doesn’t help if the breaker or outlet it’s landing on can’t handle the heat — the lowest-rated component in the circuit sets the real limit.

Aluminum Needs More Than Just a Bigger Wire Size

Upsizing aluminum wire to match copper’s ampacity isn’t the only adjustment needed — aluminum also expands and contracts more with temperature changes, which can work connections loose over time unless anti-oxidant compound and connectors rated specifically for aluminum are used. That’s why aluminum branch circuits call for different hardware, not just a larger gauge, compared to an equivalent copper run.