Should all knockout openings be removed from the box before it is mounted?

The correct understanding is that knockout openings do not need to be removed from the box before it is mounted. These knockouts are designed to provide flexibility in installation; they can be removed as needed based on the specific wiring requirements of the electrical installation. Keeping the knockouts intact until the box is installed allows the electrician to assess the proper configuration after the location of the box is determined and ensures that the box maintains its structural integrity.

Removing knockouts unnecessarily could lead to potential issues, such as compromising the enclosure's ability to protect the wiring from damage or contaminants, or creating openings that are not needed for the project at hand. Therefore, it is acceptable to leave them in place until the installation requirements dictate that they should be removed. This practice supports both safety and functionality in electrical installations.