According to NEC®, unused knockouts and other openings in electrical boxes and cabinets are required to be closed.

The requirement set forth in the NEC® (National Electrical Code) specifies that all unused knockouts and openings in electrical boxes and cabinets must be closed to ensure safety and functionality. This is crucial for several reasons.

First, leaving these openings unsealed can expose the interior components of the electrical box to dust, moisture, and potential contaminants, which can lead to deterioration and reduced performance of electrical equipment. Additionally, open knockouts can pose a safety hazard, such as the risk of electrical shock or fire, as they can allow foreign objects to enter the enclosure.

Furthermore, securing all openings contributes to maintaining the integrity of the circuit and protects against unintentional contact with live parts, which is critical in safeguarding both personnel and property.

While some might think that only certain types of openings or boxes require closure, the NEC® applies broadly to all unused knockouts and openings in electrical installations. This comprehensive approach underscores the importance of electrical safety standards in a variety of settings. Thus, the stipulation that all unused openings must be appropriately closed is vital for maintaining compliant and safe electrical systems.