What is the allowable ampacity for twenty 10 AWG THWN aluminum conductors in the same conduit at 30°C?

To determine the allowable ampacity for twenty 10 AWG THWN aluminum conductors in the same conduit at 30°C, we start with the ampacity values from the NEC (National Electrical Code) table. For 10 AWG THWN aluminum conductors, the standard ampacity in a typical installation is around 30 amps at 30°C. However, when multiple conductors are placed within the same conduit, we must consider the derating factors due to the increased heat buildup among the conductors.

According to NEC guidelines, when conducting a calculation for multiple conductors, the ampacity must be derated based on the number of conductors present:

• For three to five conductors, the ampacity is reduced to 80%.

• For six to ten conductors, it reduces to 70%.

• For eleven to twenty conductors, which is our case, the derating factor applied is typically 50%.

Given the standard rating of 30 amps for a single 10 AWG aluminum conductor, applying the 50% derating factor results in an allowable ampacity of:

30 A x 0.50 = 15 A

Thus, the allowable ampacity for twenty 10 AWG THWN aluminum conductors