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240.6

Standard Ampere Ratings

Overcurrent ProtectionNEC 2023CEC Equivalent: CEC Rule 14-104

Breakers and fuses are not manufactured in every possible ampere size. The NEC establishes a fixed set of standard ratings so that everyone in the industry is working from the same menu. The main list goes: 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. There are also additional standard fuse ratings below 15 amps — 1, 3, 6, and 10 — that are used for things like fractional-horsepower motor protection or control circuit protection. This list is critical because other sections of the code (like 240.4(B) for the next-size-up rule and 430.52 for motor OCPD) refer to it constantly when telling you to round to a standard size.

When You Need This

  • Rounding up a calculated OCPD value to the next standard size under 240.4(B)
  • Selecting the correct standard breaker size for a motor circuit per 430.52
  • Specifying breaker or fuse sizes on electrical plans and panel schedules
  • Taking any electrical exam — this list appears directly or indirectly in many calculation questions
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Key Points

1The standard sizes are: 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, 6000
2Additional fuse-only sizes below 15 A: 1, 3, 6, 10 amps
3Nonstandard ampere ratings are permitted but uncommon in practice
4This list is referenced by 240.4(B) for the next-size-up rule and 430.52 for motor OCPD rounding
5Memorizing the common residential and commercial sizes (15 through 200) will speed up exam questions significantly

Common Mistakes

Assuming that a 90-amp breaker does not exist — 90 A is on the standard list and is commonly used

Rounding to a non-standard size that is not on the list — for example, picking a 225-amp breaker when the calculation calls for the next size up from 200 and the answer is 225

Forgetting the small fuse ratings (1, 3, 6, 10 A) exist — they matter for control circuits and small motors

Confusing standard fuse and breaker ratings with standard wire sizes — they are completely different lists

Exam Tip

You do not need to memorize all 38 sizes. Focus on the residential range (15 through 200) and know that the jumps get larger above 800 (the next one is 1000, then 1200, then 1600). Many exam questions test whether you can identify the correct next-size-up from a calculation.

Frequently Asked Questions

The NEC lists 175 A as a standard size, but not all manufacturers produce breakers at every standard rating. In practice, 150 A and 200 A are far more common. However, the 175-A size does exist and shows up particularly in motor circuit calculations.

Under 240.4(B), for devices rated 800 A or less, you can round up to the next standard size. The next standard size above 62 A is 70 A, so you would select a 70-amp breaker (assuming the conductor ampacity is at least 62 A).

Inline Tools

Circuit Breaker Calculator

Find the correct OCPD size for your circuit

Related Code Sections

240.4Protection of Conductors240.4(D)Small Conductor Protection430.52Motor Branch-Circuit Short-Circuit and Ground-Fault Protection

This is an educational summary, not the official code text. The NEC® is a registered trademark and copyright © National Fire Protection Association (NFPA). The CEC is copyright © CSA Group. For official code text, visit nfpa.org or csagroup.org. SparkShift is not affiliated with NFPA or CSA Group.