Electrical
Standard Overcurrent Device Ratings
The standard ampere ratings for fuses and inverse-time circuit breakers, used when rounding a calculated value to an available device.
Source of these values
Values as commonly published for NFPA 70 240.6(A). Verify against your adopted edition.
| Standard ampere ratings |
|---|
| 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 |
In short
Standard ampere ratings for fuses and inverse-time circuit breakers begin at 15, 20, 25, 30, 35, 40, 45, 50, and 60 amperes, then continue in larger steps. A calculated value that falls between two ratings normally rounds down, with specific exceptions permitting the next size up.
Notes and limits
- Additional standard ratings for fuses include 1, 3, 6, 10, and 601 amperes.
- Where a calculated value does not correspond to a standard rating, the general rule rounds down. 240.4(B) and 430.52 contain the exceptions that permit rounding up in specific cases.
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