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Fuse & Breaker Amp Chart
Standard fuse and breaker ratings with the minimum copper conductor size and its diameter for each rating.
| Rating (A) | Min. copper wire | Diameter (mm) |
|---|
Standard: NEC Table 310.16 / 240.4(D) · Data checked: 2026-10-14
Frequently asked questions
What does the 80% rule mean here?
For a continuous load — one expected to run three hours or more — the circuit is sized at 125% of the load, so a 20 A circuit should carry no more than 16 A continuously. That is where the familiar '80% of the breaker rating' figure comes from.
Should I match the fuse to the wire or the wire to the fuse?
The wire must be at least large enough for the fuse. The fuse protects the conductor, so you size the fuse for the load and then confirm the conductor can carry it. Sizing the wire to whatever was already in the panel is how undersized circuits get built.
Why do 15 A and 20 A circuits use 14 and 12 AWG?
Because 14 AWG copper has a 60 degree C ampacity of 15 A and 12 AWG has 20 A, which matches the standard breaker sizes per NEC 240.4(D). That section sets the small-conductor limits independently of the general ampacity table.
Can I put a bigger fuse in to stop it blowing?
No. The fuse blowing is the circuit telling you the load exceeds what the wiring can safely carry. A larger fuse lets the wire overheat inside the wall where nobody sees it. Find the fault or the overload instead.