Services & DistributionQuestion 48 of 521
A transformer has a primary full-load current of 40 A and uses primary-only overcurrent protection. What is the maximum standard primary OCPD (125% rule)?
a.40 A
b.60 A
c.45 A
d.50 A
Explanation
40 A x 125% = 50 A, which is a standard size, so 50 A is the maximum per Table 450.3(B). 40 A ignores the 125% factor, while 45 A undersizes and 60 A exceeds the calculated maximum.
Law Reference: 2023 NEC §450.3(B)Practice all 521 questions free — no signup required.
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