What is the basis for volume allowance when internal cable clamps are present in the box?

The correct answer is based on the NEC guidelines regarding volume allowances for conductors when internal cable clamps are present in an outlet or junction box. When determining the volume allowance for a box, it is essential to consider the largest conductor present. This is because the size of the largest conductor dictates the space required in the box to ensure proper installation and to prevent overcrowding and overheating. The NEC guidelines recognize that larger conductors occupy more space, and by using the largest conductor for calculating the volume allowance, you help ensure compliance with safe electrical practices.

In contrast, using the smallest conductor would not provide sufficient room for the electrical connections and other conductors, potentially leading to unsafe conditions. The average size or assuming no volume allowance is necessary does not adequately account for the physical constraints imposed by the largest conductor, which is crucial for maintaining proper installation standards as specified in the NEC.