Question 8066 of 731 · Texas Journeyman Electrician Exam
A 45 kVA, 480 volt three-phase transformer has primary-only protection. What is the maximum standard primary breaker size?
Exactly one answer is correct.
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Correct answer to question 8066
- C: 70 A
Explanation
Primary current is 45,000 VA divided by (480 V times 1.732), which is about 54.1 A. Table 450.3(B) allows 125 percent, or 67.7 A, and its note permits the next higher standard size of 70 A.
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