Unused openings in panelboards can be closed using what?

Unused openings in panelboards must be closed with listed fillers. The requirement for using listed fillers ensures that the materials used are appropriate and compliant with safety standards set by the National Electrical Code (NEC) or other relevant authorities. Listed fillers are specifically designed for this purpose, as they help maintain the integrity of the panelboard's construction, protect against dust and other contaminants, and minimize potential hazards such as electrical arcing.

Using unlisted products or unsuitable materials, such as plastic tape, cardboard, or non-listed fillers, could compromise the safety and performance of the electrical installation. This could lead to issues such as overheating, increased risk of electrical faults, or providing a pathway for moisture and debris which could affect the internal components of the panelboard. Therefore, using listed fillers is not only a best practice but also a requirement for ensuring electrical installations meet regulatory standards.