Determine the ampacity for six 8 AWG THW copper conductors in EMT at an ambient temperature of 30°C.

To determine the ampacity for six 8 AWG THW copper conductors in EMT at an ambient temperature of 30°C, it is essential to first refer to the National Electrical Code (NEC) tables that provide the standard ampacity for conductors based on their size, insulation type, and installation conditions.

For 8 AWG copper conductors, the base ampacity listed in Table 310.16 at 30°C is typically around 40 amps. This value is relevant for conductors that are installed under standard conditions without any derating factors considered, such as the number of conductors in a raceway or the ambient temperature being higher than 30°C.

However, when multiple conductors are installed together, like six 8 AWG conductors in an EMT conduit, you must apply a derating factor to account for the increased heat buildup among the conductors. According to NEC guidelines, six conductors would require a 10% derating. Thus, you would calculate the derated ampacity as follows:

1. Start with the base ampacity for one conductor, which is 40 A.

2. Apply the 10% derating: 40 A - (10% of 40 A) =