Wire Derating Chart [extra Quality] Link

1. The Setup: A Perfectly Rated Circuit An electrician named Alex finishes wiring a new commercial kitchen. He runs a 12 AWG copper wire — rated for 20 amps at room temperature — from the breaker panel to a dedicated outlet for a large mixer. By the book, 12 AWG + 20A breaker = safe, legal, functional.

That’s the new maximum before insulation damage. But the breaker is 20A, so the circuit is limited to 20A anyway. wire derating chart

At 55°C ambient, the factor is .

However, if the mixer draws 16A continuously (more than 3 hours), the wire must be derated again by 125% — but here, 16A is fine. But Alex realizes: — because the breaker is thermal and also affected by ambient heat. 4. The Multiplier Trap Alex also has four current-carrying conductors in the same conduit (not just two). Table 310.15(C)(1) says: 4–6 conductors → derate by 0.80. By the book, 12 AWG + 20A breaker = safe, legal, functional