Which of the following is necessary for a box to be considered able to support an outlet box containing devices or luminaires?

For a box to be considered able to support an outlet box containing devices or luminaires, it is essential that it meets specific structural requirements outlined in the NEC. The presence of two intermediates refers to the need for additional supports or reinforcements within the box itself. This is critical because the weight of the devices or luminaires can exert significant forces, and having adequate structural support is necessary to ensure safety and functionality.

Proper support mechanisms within an electrical box help prevent any movement or displacement over time that could lead to wiring issues or hazards. These intermediates, which can take the form of horizontal bracing or reinforced components as prescribed by the NEC, are necessary to distribute load and maintain the integrity of the installation.

The other choices do encompass qualities that may be beneficial to a box, such as being attached to a stud for enhanced stability or having a rigid base, but they do not encompass the core requirement of support outlined in the NEC regarding outlet boxes for devices or luminaires. Therefore, the correct answer focuses on the essential support structure requirement crucial for safe electrical installations.