What is the ampacity of three 8 AWG THWN copper conductors installed in EMT at an ambient temperature of 30°C if they are all current-carrying conductors?

To determine the ampacity of three 8 AWG THWN copper conductors installed in Electrical Metallic Tubing (EMT) at an ambient temperature of 30°C, it is essential to refer to the National Electrical Code (NEC) guidelines which provide the necessary ampacity values for various conductors and installation conditions.

For 8 AWG THWN conductors, the base ampacity at 30°C is typically around 55 A, based on NEC Table 310.16. However, since the question specifies that all three conductors are current-carrying, we must apply the appropriate adjustment factors due to the presence of multiple conductors.

According to NEC Article 310.15, when more than three conductors are installed together in a conduit, an adjustment factor is required for the ampacity. For three current-carrying conductors, the adjustment factor is typically 70%. Thus, the calculation is as follows:

1. Start with the base ampacity for a single 8 AWG THWN copper conductor, which is 55 A at 30°C.

2. Apply the adjustment factor: 55 A x 0.7 = 38.5 A.

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