What is the minimum size THWN-2 ungrounded feeder conductor required for a 150-ampere rated panel board in a 208Y/120-volt system?

To determine the minimum size of a THWN-2 ungrounded feeder conductor for a 150-ampere rated panel board in a 208Y/120-volt system, we rely on the National Electrical Code (NEC) and its guidelines for sizing conductors based on the ampacity required for different applications.

For a 150-ampere load, THWN-2 copper conductors are typically utilized. When checking the NEC ampacity tables, specifically Table 310.16, it shows that a 1 AWG copper conductor is rated to carry 130 amperes in a standard installation scenario under typical conditions. However, when factors for temperature or installation conditions are considered, the minimum rating and size can be affected.

In this case, a 1 AWG THWN-2 conductor provides a safe and compliant capacity to handle the continuous load associated with a 150-ampere panel board. Additionally, conductors are generally chosen considering the potential for derating based on the number of conductors in a raceway, ambient temperature, and other installation factors. Thus, a 1 AWG copper conductor is a prudent choice for safely supporting a 150-ampere load while adhering to NEC guidelines.

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