Fundamental Code Calculations Practice Test 2026 - Free Code Calculations Practice Questions and Study Guide

To determine the ampacity of a 12 AWG THWN-2 copper conductor, one must refer to the National Electrical Code (NEC) tables, which provide ampacity ratings based on various factors, including conductor size, insulation type, and installation conditions.

For a standard 12 AWG THWN-2 copper conductor, under typical conditions, the ampacity is 20 A. However, it's important to consider the specific termination temperature. When connected to a circuit breaker with a termination temperature rating of 60°C/75°C, the ampacity can be adjusted according to the NEC guidelines based on the ambient temperature and the insulation type.

The adjustment factors for THWN-2 insulation allow for slightly higher ratings at the 75°C termination than at 60°C. As such, the ampacity for a 12 AWG THWN-2 conductor permits continuous loads at a rating of 25 A when accounting for these conditions. This makes the option indicating 25 A the correct choice, as it reflects the conductor's ability to handle that level of current safely under the specified termination temperature.

In summary, the ampacity of a 12 AWG THWN-2 copper conductor is influenced by both the conductor's size and type