Equipment & SystemsQuestion 299 of 521
For the 15 kVA, 480 V single-phase transformer (primary current 31.25 A), what is the maximum primary-only overcurrent device using the 125% factor of Table 450.3(B)?
a.31.25 A
b.46.9 A
c.39.1 A
d.62.5 A
Explanation
Primary current >=9 A limits primary-only protection to 125%: 31.25 x 1.25 = 39.1 A (next standard size up permitted where needed). 31.25 A omits the factor, 46.9 A is 150%, and 62.5 A is 200%.
Law Reference: 2023 NEC §450.3Practice all 521 questions free — no signup required.
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