Question 13050 of 749 · Maryland Journeyperson Electrician Exam
What is the ampacity of 4 AWG THWN copper (75 °C insulation) with three current-carrying conductors at an ambient of 45 °C?
Exactly one answer is correct.
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Correct answer to question 13050
- B: 69.7 A
Explanation
THWN is a 75 °C insulation, so the base ampacity is 85 A and the 75 °C correction factor for 41 to 45 °C is 0.82: 85 x 0.82 = 69.7 A. Using the 90 °C factor 0.87 gives 74.0 A, which does not apply to THWN.
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