Master Electrician Practice Exam

For a size 750 kcmil XHHW aluminum conductor with six current-carrying conductors, what is the maximum allowable ampacity in a dry location at 22 degrees C?

1. 350.5 amperes

2. 361.92 amperes

3. 375.2 amperes

4. 400 amperes

The correct answer is: 361.92 amperes

To determine the maximum allowable ampacity for a 750 kcmil XHHW aluminum conductor with six current-carrying conductors in a dry location at 22 degrees Celsius, it's essential to first refer to the National Electrical Code (NEC) tables that specify ampacity based on conductor size, insulation type, and the number of conductors present. The basic ampacity for a 750 kcmil aluminum conductor can be found in NEC Table 310.16 (or the equivalent source relevant to the exam context). However, the specified value needs to be adjusted based on the number of conductors being installed together. The NEC has correction factors for ampacity when more than three conductors are installed in the same raceway or cable. In the case of six current-carrying conductors, the NEC requires applying a derating factor to account for the increase in temperature due to the proximity of the conductors. The typical derating factor for six conductors is 0.67. Assuming an initial ampacity of around 540 amperes for a single conductor, when you apply the derating factor, the calculations proceed as follows: 540 amperes * 0.67 = 361.8 amperes. This would round