How Many Amps Can 12 Gauge Wire Handle?

The standard answer: 20A for 12 AWG copper

Standard ampacity tables rate 12 AWG copper conductors for 20A at 60C, 25A at 75C, and 30A at 90C insulation ratings. In practice, most residential circuit breakers and equipment terminals are only rated for 60C or 75C, which is why 12 AWG circuits are almost universally protected by a 20A breaker, not higher, regardless of the wire's 90C column rating.

Why you can't just use the 90C column

Even if your wire is rated 90C (common THHN insulation), the breaker, panel bus and receptacle terminals it connects to are typically only listed for 60C or 75C. Code requires using the lower of the two temperature ratings, which is almost always the terminal's rating, not the wire's own insulation rating.

How ambient heat and bundling change the real number

12 AWG wire run through a hot attic (41-45C ambient) bundled with 5 other current-carrying conductors sees its ampacity drop from 25A (75C base) to roughly 25 × 0.82 × 0.8, about 16.4A - below what a standard 20A breaker on that circuit assumes. This is exactly what the Wire Ampacity Calculator is built to check.

Copper vs aluminum: not the same number

12 AWG aluminum wire has a lower ampacity than copper at the same gauge - aluminum's higher resistance means it needs a larger cross-section to carry the same current safely. Aluminum branch circuit wiring is uncommon at 12 AWG (more typical at larger feeder sizes) precisely because the gauge-for-gauge capacity difference makes it impractical for small branch circuits.

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