According to 110.14(C), conductors are to be sized to the lowest temperature rating of any terminal, device, or conductor of the circuit, in accordance with the equipment terminal temperature rating. However, conductors with insulation temperature ratings higher than the termination's temperature rating can be used for conductor ampacity adjustment, correction, or both.
The ampacity of each 12 THHW conductor in a dry location is 30A, based on the values listed in the 90°C column of Table 310.16. If we bundle nine current-carrying 12 THHN conductors, the ampacity for each conductor needs to be adjusted by a 70% adjustment factor.
Adjusted conductor ampacity = 30A × 0.70 = 21A
But under one hundred amps we have to use the 60° column which puts #12 at 20 amps
So the correct answer is twenty amps???
The ampacity of each 12 THHW conductor in a dry location is 30A, based on the values listed in the 90°C column of Table 310.16. If we bundle nine current-carrying 12 THHN conductors, the ampacity for each conductor needs to be adjusted by a 70% adjustment factor.
Adjusted conductor ampacity = 30A × 0.70 = 21A
But under one hundred amps we have to use the 60° column which puts #12 at 20 amps
So the correct answer is twenty amps???