Circuit Breaker Size Chart — NEC 240.6(A) Standard Ratings & Wire Pairings
Standard circuit breaker ampere ratings per NEC 240.6(A), small-conductor limits, and minimum copper wire sizes computed from NEC 310.16.
Updated August 22, 2026
Breakers and fuses come in standardized ampere ratings so that conductor protection rules have fixed steps to land on. NEC Table 240.6(A) lists 37 standard ratings from 15 A to 6000 A — the familiar residential ladder (15, 20, 30, 40, 50…) plus the feeder and service sizes — and adds five fuse-only ratings (1, 3, 6, 10, and 601 A). Nonstandard ratings are permitted, but the standard list is what the round-up allowance in 240.4(B) keys on: when a conductor’s ampacity does not match a standard rating, the next higher standard device is allowed, provided the circuit is not a multi-receptacle branch circuit for portable loads and the selected rating does not exceed 800 A.
The pairing table below is computed, not copied: for each breaker rating it walks NEC Table 310.16 (as encoded in our conductor ampacity calculator), applies the 240.4(B) round-up where it legally fits, and enforces the 240.4(D) small-conductor caps that hold 14, 12, and 10 AWG copper to 15, 20, and 30 A no matter what the ampacity table says. It assumes copper, not more than three current-carrying conductors, 30 °C ambient, and no derating — real installations with long runs, hot attics, bundled cables, or continuous loads need the corrections the calculator applies. Where the 240.4(B) conditions are not met, step up one conductor size.
NEC Table 240.6(A) — Standard Ampere Ratings
| Band | Standard ratings (A) |
|---|---|
| 15–50 A | 15, 20, 25, 30, 35, 40, 45, 50 |
| 60–110 A | 60, 70, 80, 90, 100, 110 |
| 125–250 A | 125, 150, 175, 200, 225, 250 |
| 300–600 A | 300, 350, 400, 450, 500, 600 |
| 700–1200 A | 700, 800, 1000, 1200 |
| 1600–6000 A | 1600, 2000, 2500, 3000, 4000, 5000, 6000 |
Fuses and inverse-time circuit breakers. Additional standard ratings for FUSES only: 1, 3, 6, 10, and 601 A. Nonstandard ratings are permitted (240.6(A)).
NEC 240.4(D) — Small-Conductor Overcurrent Limits
| Conductor | Max OCPD (A) |
|---|---|
| 14 AWG copper | 15 |
| 12 AWG aluminum / Cu-clad Al | 15 |
| 12 AWG copper | 20 |
| 10 AWG aluminum / Cu-clad Al | 25 |
| 10 AWG copper | 30 |
18 AWG copper (7 A) and 16 AWG copper (10 A) carry additional conditions in 240.4(D)(1)–(2): continuous-load limits of 5.6 A / 8 A and listed OCPD marked for the wire, or Class CC/J/T fuses. These caps apply after any ambient or bundling correction.
Minimum Copper Conductor per Breaker Rating (Computed from NEC 310.16)
| Breaker | Min Cu, 60 °C terminations | Min Cu, 75 °C terminations |
|---|---|---|
| 15 A | 14 AWG | 14 AWG |
| 20 A | 12 AWG | 12 AWG |
| 25 A | 10 AWG | 10 AWG |
| 30 A | 10 AWG | 10 AWG |
| 35 A | 8 AWG | 8 AWG |
| 40 A | 8 AWG | 8 AWG |
| 45 A | 6 AWG | 8 AWG |
| 50 A | 6 AWG | 8 AWG |
| 60 A | 6 AWG | 6 AWG |
| 70 A | 4 AWG | 6 AWG |
| 80 A | 3 AWG | 4 AWG |
| 90 A | 3 AWG | 4 AWG |
| 100 A | 2 AWG | 3 AWG |
| 110 A | 1 AWG | 2 AWG |
| 125 A | 1/0 AWG | 2 AWG |
| 150 A | 2/0 AWG | 1 AWG |
| 175 A | 3/0 AWG | 2/0 AWG |
| 200 A | 4/0 AWG | 3/0 AWG |
| 225 A | 250 kcmil | 4/0 AWG |
| 250 A | 300 kcmil | 4/0 AWG |
| 300 A | 350 kcmil | 250 kcmil |
| 350 A | 500 kcmil | 350 kcmil |
| 400 A | — | 500 kcmil |
Computed from NEC Table 310.16 with the 240.4(B) next-higher-standard-rating allowance and the 240.4(D) caps applied in code. Assumes ≤3 current-carrying conductors, 30 °C ambient, no derating, load within conductor ampacity. “—” = no conductor in the 14 AWG–500 kcmil range qualifies at that termination rating.
Sources & Further Reading
- NEC (NFPA 70), Table 240.6(A) — Standard Ampere Ratings, 240.4(B), and 240.4(D), digit-verified against the licensed 2017 Article 240 text and 2023-edition reproductions (electricallicenserenewal.com; up.codes) — the ratings list and caps are unchanged between editions
- NEC (NFPA 70) 2023, Table 310.16 — as encoded and verified in the conductor ampacity calculator (the generated pairing table derives from its AMPACITY_TABLE export)
- Published pairing cross-checks: PES Supply breaker/wire-size chart (75 °C THHN/THWN-2 column) and Mike Holt’s published 240.4(B) examples (6 AWG at 70 A; 1 AWG at 150 A)
Frequently Asked Questions
Why can 8 AWG copper sit on a 50 A breaker in one house and need 6 AWG in another?
Termination temperature. With 75 °C terminations and THHN/THWN-2 wire, 8 AWG copper is good for 50 A. But NM-B cable (Romex) must be used at the 60 °C column per NEC 334.80, where 8 AWG is only 40 A — so a 50 A circuit wired in NM-B needs 6 AWG. That is exactly why the pairing table carries both columns.
What does the 240.4(B) “next size up” rule actually allow?
When a conductor’s ampacity is not a standard rating — say 6 AWG copper at 65 A — you may protect it with the next higher standard device, a 70 A breaker, provided the circuit is not a multi-receptacle branch circuit for cord-and-plug loads and the device does not exceed 800 A. It never works the other way: a 70 A load still needs a conductor rated at least 70 A after corrections.
Why is 12 AWG copper limited to a 20 A breaker when Table 310.16 shows 25 or 30 A?
NEC 240.4(D) overrides the ampacity table for small conductors: 14, 12, and 10 AWG copper are capped at 15, 20, and 30 A regardless of the insulation column. The higher table values still matter as the starting point for derating — a bundled or hot-attic 12 AWG THHN starts derating from 30 A — but the breaker cap stands after every correction.
Are 25, 35, and 45 A breakers real? I never see them in panels.
They are standard ratings in Table 240.6(A) and manufacturers list them, but distributors stock the even ladder (20/30/40/50) so the odd sizes are special-order. They show up where the arithmetic demands them — motor and air-conditioner circuits sized per nameplate frequently land on 25, 35, or 45 A maximum-OCPD values.
Try the Calculators
Circuit Breaker Size Chart — NEC 240.6(A) Standard Ratings & Wire Pairings — reuven.tools/reference/breaker-sizes — verified against: NEC (NFPA 70), Table 240.6(A) — Standard Ampere Ratings, 240.4(B), and 240.4(D), digit-verified against the licensed 2017 Article 240 text and 2023-edition reproductions (electricallicenserenewal.com; up.codes) — the ratings list and caps are unchanged between editions; NEC (NFPA 70) 2023, Table 310.16 — as encoded and verified in the conductor ampacity calculator (the generated pairing table derives from its AMPACITY_TABLE export); Published pairing cross-checks: PES Supply breaker/wire-size chart (75 °C THHN/THWN-2 column) and Mike Holt’s published 240.4(B) examples (6 AWG at 70 A; 1 AWG at 150 A)