Fundamentals of Code Calculations Practice Test 2025 – Your All-in-One Guide to Exam Success!

To determine the ampacity of a single 1/0 AWG THW aluminum conductor installed in free air at an ambient temperature of 104°F, it's important to refer to standard ampacity charts which take into account the size of the conductor, the type of insulation, and the installation conditions.

For a 1/0 AWG aluminum conductor, the base ampacity, when operating under typical conditions (usually at 30°C or about 86°F), is usually around 170 A to 180 A. However, since the installation is in free air and at a higher ambient temperature of 104°F, we must adjust this base value downwards due to the derating rules defined by the National Electrical Code (NEC) or applicable local codes.

At elevated ambient temperatures, the capacity of the conductor to effectively carry current without overheating diminishes. For a temperature rating increase, ampacity typically decreases. By consulting specific ampacity tables, one would find the suggested adjustments for both temperature and installation method.

In this case, for a 1/0 AWG aluminum conductor in free air at 104°F, the adjusted ampacity comes out to approximately 158 A, which aligns with the choice indicated. This value reflects the necessary