Breaker Sizes Chart

Standard Ampere Ratings (NEC 240.6)

Breakers are manufactured only in the ratings listed — the series is fixed by NEC 240.6, not by what would be convenient. There is no 55 A, 65 A, 75 A or 90 A breaker in the standard series, so a calculated load must be rounded up to the next standard size.

The continuous-load column is 80% of the rating, because a breaker carrying a continuous load (three hours or more) may be loaded only to 80% of its rating unless the assembly is listed for 100%. Equivalently, the breaker must be at least 125% of the continuous load — which is the inverse-time column.

Standard ratings above 1,200 A are normally only available as adjustable-trip moulded case or insulated case breakers, where the rating is set within a range rather than fixed.

Why the Rating Must Be Rounded Up

A branch circuit's overcurrent device must protect the conductor. The conductor's ampacity comes from the ampacity table, adjusted for ambient temperature and the number of conductors in the raceway — and the breaker must not exceed that adjusted ampacity.

The practical sequence is: calculate the load, apply the 125% factor for continuous loads, then select the next standard size up. That last step matters because the calculated figure almost never lands on a standard rating. A 42 A continuous load needs 52.5 A, which rounds to a 60 A breaker — and the conductor must then be sized to carry 60 A, not 52.5 A.

One exception is worth knowing: the next-size-up rule may be applied to the next standard rating only, not the one after. A load that needs 130 A cannot be served by a 150 A breaker on a 125 A conductor — the conductor must be increased instead.

Frequently Asked Questions

What are the standard circuit breaker sizes?

15, 20, 25, 30, 35, 40, 45, 50, 60, 70, 80, 90, 100, 110, 125, 150, 175, 200, 225, 250, 300, 350, 400, 450, 500, 600, 700, 800, 1000, 1200, 1600, 2000, 2500, 3000, 4000, 5000 and 6000 amperes, per NEC 240.6.

Why is there no 55 amp breaker?

Because the standard series is fixed and does not include it. The gaps widen as the ratings rise: 225 to 250, then 250 to 300, then 300 to 350. A load between two standard sizes must be served by the next size up, with the conductor sized accordingly.

What is the 80% rule for breakers?

A breaker may carry a continuous load — one lasting three hours or more — at no more than 80% of its rating. So a 20 A breaker carries 16 A continuously. Equivalently, the breaker must be sized at 125% of the continuous load. Non-continuous loads may use the full rating.

Can I use a larger breaker than the conductor rating?

Generally no — the breaker protects the conductor. The exception is motors, where the short-circuit protection may be sized well above the conductor ampacity because the motor's overload relay provides the overload protection. That exception is specific to motor circuits.

What is an adjustable-trip breaker?

A breaker whose trip rating can be set within a range, rather than being fixed at manufacture. Above 1,200 A they are the norm, which is why the standard series becomes less meaningful at high ratings — the breaker is set to the calculated value rather than selected from a list.

Related

• Wire Ampacity Chart
• Copper Properties
• Conduit Fill Chart
• Voltage Drop Calculator
• Cable Sizes

Value Sources

References and calculation methods used for this page are listed below. Numbered markers connect table columns where present. A reference listing does not itself establish that every value has been independently checked.

Data Sources

Verification scope

No page-specific independent source review is recorded here. The listed references and formulas explain the basis of the compilation; automated consistency checks do not verify the original sources or establish product conformity.

Derived values — the following values on this page are calculated, not taken directly from the standard:

Ratings are the standard series only. Selecting a breaker requires the calculated load, the conductor ampacity after adjustment, and the applicable code article. Above 1,200 A most breakers are adjustable-trip and the rating is set rather than selected.

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