What is the ampacity of each of the nine 8 AWG THHN copper conductors supplying three 3-phase motors in RMC at 30°C?

What is the ampacity of each of the nine 8 AWG THHN copper conductors supplying three 3-phase motors in RMC at 30°C?

• A. 38.5 A
• B. 50 A
• C. 44 A
• D. 60 A

Answer: (A)

To determine the ampacity of 8 AWG THHN copper conductors at a temperature of 30°C, it's essential to refer to the National Electrical Code (NEC) or similar wiring standards, which provide ampacity tables. For 8 AWG copper wire, typically used in residential and commercial electrical installations, the ampacity at 30°C is approximately 50 amps. However, when calculating ampacity for three-phase motors, the requirements might slightly differ based on factors such as continuous versus non-continuous loads, and any derating that may apply due to grouping of conductors or ambient temperature adjustments. In this context, the reference to 38.5 A suggests that the value could be a result of additional adjustments or considerations, such as a continuous load factor or specific installation conditions (e.g., conduit fill, ambient temperature considerations). While 50 A is the base ampacity for the wire under standard conditions, when conducting load calculations for multiple motors, the total derating factors can lower this number. Therefore, the calculated value of 38.5 A likely reflects these considerations, aligning with the practices followed for allowing a safety margin and ensuring the conductors do not overheat. Thus, the correct answer indicates

To determine the ampacity of 8 AWG THHN copper conductors at a temperature of 30°C, it's essential to refer to the National Electrical Code (NEC) or similar wiring standards, which provide ampacity tables.

For 8 AWG copper wire, typically used in residential and commercial electrical installations, the ampacity at 30°C is approximately 50 amps. However, when calculating ampacity for three-phase motors, the requirements might slightly differ based on factors such as continuous versus non-continuous loads, and any derating that may apply due to grouping of conductors or ambient temperature adjustments.

In this context, the reference to 38.5 A suggests that the value could be a result of additional adjustments or considerations, such as a continuous load factor or specific installation conditions (e.g., conduit fill, ambient temperature considerations).

While 50 A is the base ampacity for the wire under standard conditions, when conducting load calculations for multiple motors, the total derating factors can lower this number. Therefore, the calculated value of 38.5 A likely reflects these considerations, aligning with the practices followed for allowing a safety margin and ensuring the conductors do not overheat.

Thus, the correct answer indicates