Which of the following is not a standard size fuse or time inverse circuit breaker according to the NEC?

• A. 55 amp (240.6A)
• B. 60 amp
• C. 50 amp
• D. 70 amp

Answer: (A)

The concept being tested is understanding that the NEC designates a fixed set of standard ampere ratings for fuses and inverse-time circuit breakers. This standard set is defined so protective devices are interchangeable and easy to replace across installations. In the NEC’s standard list, common sizes include 50 A, 60 A, 70 A, and other specific ratings, but fifty-five amps is not one of them. That’s why fifty-five amps is not considered a standard size. In practice, if a calculation lands near 55 A, you would choose the next higher standard rating (typically 60 A) to maintain proper protection. The other options align with the NEC’s standard sizes, which is why they are considered standard.