When twenty 12 AWG copper THNN conductors are installed in a 2" EMT, what percent is the ampacity rating of each conductor de-rated?

To determine the correct de-rating percentage for twenty 12 AWG copper THHN conductors installed in a 2" EMT (Electrical Metallic Tubing), it is important to refer to the National Electrical Code (NEC) guidelines, specifically the ampacity tables and the rules governing conductor installations.

When multiple conductors are bundled together or installed in conduit, their ability to dissipate heat decreases due to reduced air circulation and increased thermal accumulation. This necessitates a de-rating of their ampacity to prevent overheating and potential hazards. The NEC provides specific factors for de-rating based on the number of conductors present in a conduit.

For installation where there are more than three conductors, the NEC stipulates that the maximum allowable ampacity of each conductor must be adjusted. According to NEC Table 2 in Chapter 9, specifically for 12 AWG conductors, when you have more than three conductors (in this case, twenty), the ampacity is typically required to be reduced to 50% of the standard capacity.

This means that when twenty 12 AWG conductors are installed, each conductor's ampacity is reduced significantly, leading to a 50% de-rating. This reduction ensures that the conductors can safely operate without