Residential Wire Size Chart (Ampacity Quick Reference)
A field-reference rundown of the common residential conductor sizes, their typical breaker ratings, and the everyday circuits they serve — plus the derating and terminal-rating gotchas that trip people up. Always verify against the NEC and local amendments.
Written by Steven Rotan
Licensed Journeyman Electrician — Oregon #883LR
⚠️ Before you start
- This is a quick reference for common residential 60°C/75°C copper applications — not a substitute for the NEC ampacity tables, correction/adjustment factors, and local amendments. Always verify for your actual conditions.
- Ampacity depends on conductor material, insulation temperature rating, terminal rating, ambient temperature, and the number of current-carrying conductors bundled together. Derating can move the answer.
- Aluminum has different ampacity than copper for the same size — never assume a copper chart applies to aluminum.
Every electrician keeps a version of this in their head, but it's worth having the reasoning behind the numbers — and the caveats that turn a "simple" chart into a code violation if you ignore them. This is a field quick reference, not a replacement for the NEC tables and your local amendments.
Common residential copper sizes
For typical residential branch circuits (copper conductors):
| Breaker | Copper AWG | Typical use |
|---|---|---|
| 15 A | 14 AWG | Lighting, general receptacles |
| 20 A | 12 AWG | Kitchen/bath/laundry receptacles, small appliance circuits |
| 30 A | 10 AWG | Electric dryer, water heater, some AC |
| 40 A | 8 AWG | Ranges, larger AC, some EV chargers |
| 50 A | 6 AWG | Ranges, ovens, EV chargers, subpanel feeders |
That's the well-worn shorthand behind "14-2 for lights, 12-2 for outlets." Larger services and feeders (100 A, 200 A) step up from there.
Why the wire size alone isn't the whole answer
The chart is a starting point. Real ampacity depends on:
- Insulation temperature rating — the 60°C / 75°C / 90°C column you're allowed to use.
- Terminal rating — your breakers and devices are often rated 60°C or 75°C, which limits you to that column's value even if the wire's insulation is rated higher.
- Ambient temperature — hot attics and equipment rooms force corrections.
- Number of current-carrying conductors bundled or in conduit — more than three triggers adjustment (derating).
- Copper vs. aluminum — aluminum carries less for the same size; never apply a copper chart to aluminum.
Any of these can push you to a larger conductor than the base chart suggests.
Don't forget voltage drop
Ampacity keeps the wire from overheating. It says nothing about voltage drop, which on long runs can be a problem even when ampacity is fine. The NEC recommends keeping branch-circuit drop to about 3% (≈5% total with the feeder). For long home runs — a detached garage, a well pump, a run across a big house — you often upsize for voltage drop, not ampacity. See our voltage drop explained guide and calculator.
Bottom line
Memorize the base chart — 14/15, 12/20, 10/30, 8/40, 6/50 (copper) — but treat it as the beginning of the sizing conversation, not the end. Check your terminal rating and column, apply derating for ambient and conductor count, account for aluminum, and upsize for voltage drop on long runs. And always confirm against the current NEC and local amendments for the actual installation.
📞 When to call a professional
This reference is for electricians and knowledgeable DIYers. Any doubt about sizing for a specific load, long run (voltage drop), or derating condition should be confirmed by a licensed electrician against the current code.
Frequently asked questions
What size wire for a 15, 20, 30, 40, and 50 amp circuit?
The common residential copper rule-of-thumb: 15A = 14 AWG, 20A = 12 AWG, 30A = 10 AWG, 40A = 8 AWG, 50A = 6 AWG. These reflect the 60°C column typically applied to residential branch circuits, and the well-known '14-2 for lights, 12-2 for outlets' shorthand. Larger loads (100A, 200A services and feeders) step up further. Always confirm against the NEC table and any derating.
Why can't I just go by the wire size alone?
Because ampacity depends on more than gauge: the insulation's temperature rating (60/75/90°C column), the terminal rating of your devices and breakers (often limiting you to the 60°C or 75°C value), ambient temperature, and how many current-carrying conductors are bundled or in conduit (which forces derating). Copper vs. aluminum matters too. The chart is a starting point; conditions can require a bigger conductor.
What about voltage drop on long runs?
Ampacity keeps the wire from overheating, but on long runs voltage drop can still be a problem even when the ampacity is fine — the NEC recommends keeping branch-circuit voltage drop to about 3% (5% total with the feeder). For long home runs (detached garage, well pump, a run across a big house) you often upsize the conductor for voltage drop, not ampacity. See our voltage drop guide and calculator.
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