Question 1

Using NEC Table 310.16, what is the ampacity of a 6 AWG THWN-2 copper conductor in a raceway with no more than 3 current-carrying conductors at an ambient temperature of 30°C?

Accepted Answer

65 amperes (NEC NEC Table 310.16). NEC Table 310.16 specifies 65A for 6 AWG THWN-2 copper at 30°C with 3 or fewer conductors.

Question 2

A 3 AWG THHN copper conductor has an ampacity of 115A per Table 310.16 at 30°C. If the ambient temperature is 40°C, what is the corrected ampacity? (Correction factor for 36-40°C for 90°C rated conductor = 0.91)

Accepted Answer

104.7 amperes (NEC NEC Table 310.16, Table 310.15(B)(1)(1)). Per Table 310.16, 3 AWG THHN (90°C) = 115A. Per Table 310.15(B)(1)(1), correction factor for 36-40°C ambient at 90°C = 0.91. Corrected ampacity = 115A × 0.91 = 104.65A ≈ 104.7A.

Question 3

Six current-carrying conductors are installed in the same raceway. Per NEC Table 310.15(C)(1), what is the adjustment factor that must be applied to the conductor ampacity?

Accepted Answer

80% (NEC NEC Table 310.15(C)(1)). NEC Table 310.15(C)(1) requires 80% adjustment for 4-6 current-carrying conductors in the same raceway.

Question 4

A raceway contains 9 current-carrying THHN copper conductors in an ambient temperature of 35°C. Per NEC Table 310.15(C)(1), what adjustment factor applies for 9 conductors?

Accepted Answer

70% (NEC NEC Table 310.15(C)(1)). NEC Table 310.15(C)(1) requires a 70% adjustment factor for 7-9 current-carrying conductors in the same raceway.

Question 5

A 4 AWG THHN copper conductor (rated 90°C) has an ampacity of 95A per Table 310.16 at 30°C. If 6 current-carrying conductors are in the same raceway AND the ambient temperature is 40°C (correction factor = 0.91 for 90°C column), what is the final adjusted ampacity?

Accepted Answer

69.2A (NEC NEC Table 310.16, 310.15(C)(1)). Apply both factors: 95A × 0.80 (6 conductors) × 0.91 (40°C ambient) = 69.2A. Both temperature correction and conduit fill adjustment must be applied.

Practice Questions: Wire Ampacity