What does Section 110.12(A) require for unused openings in equipment boxes?

Section 110.12(A) of the National Electrical Code (NEC) addresses the requirement for unused openings in equipment boxes. This regulation mandates that any unused openings must be closed. The rationale behind this requirement is primarily related to safety and functionality. Closing these openings prevents the entrance of dust, debris, or moisture, which could potentially cause short circuits or degrade the equipment inside the box. By ensuring that all unused openings are properly sealed, the likelihood of electrical hazards is minimized, promoting safer installations.

Other options do not comply with this requirement. For instance, leaving openings uncovered or allowing them to remain open would expose the internal components to potential contaminants and risks. Capping openings might be permissible in certain contexts, but it does not fulfill the explicit requirement for them to be securely closed as specified in the code. Therefore, the correct interpretation aligns with keeping all unused openings properly closed.