QuestionMay 21, 2025

What's the ampacity of one wire in a cable consisting of three type THW No. 8 copper wires in an ambient temperature of 70^circ C A) 15.0 A B) 18.5 A C) 21.6 A D) 16.5 A

What's the ampacity of one wire in a cable consisting of three type THW No. 8 copper wires in an ambient temperature of 70^circ C A) 15.0 A B) 18.5 A C) 21.6 A D) 16.5 A
What's the ampacity of one wire in a cable consisting of three type THW No. 8
copper wires in an ambient temperature of
70^circ C
A) 15.0 A
B) 18.5 A
C) 21.6 A
D) 16.5 A

Solution
3.9(333 votes)

Answer

23.2 A Explanation 1. Determine Base Ampacity Type THW No. 8 copper wire has a base ampacity of 40 A at 30^{\circ}C. 2. Apply Temperature Correction Factor For an ambient temperature of 70^{\circ}C, use the correction factor from NEC tables, which is 0.58 for THW insulation. 3. Calculate Corrected Ampacity Multiply base ampacity by correction factor: 40 \, \text{A} \times 0.58 = 23.2 \, \text{A}. 4. Apply Adjustment for More Than Three Conductors Since there are three conductors, no adjustment is needed beyond the temperature correction.

Explanation

1. Determine Base Ampacity<br /> Type THW No. 8 copper wire has a base ampacity of 40 A at $30^{\circ}C$.<br /><br />2. Apply Temperature Correction Factor<br /> For an ambient temperature of $70^{\circ}C$, use the correction factor from NEC tables, which is 0.58 for THW insulation.<br /><br />3. Calculate Corrected Ampacity<br /> Multiply base ampacity by correction factor: $40 \, \text{A} \times 0.58 = 23.2 \, \text{A}$.<br /><br />4. Apply Adjustment for More Than Three Conductors<br /> Since there are three conductors, no adjustment is needed beyond the temperature correction.
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