For junction boxes exceeding 100 cu in., how far must screws penetrate the wall?

For junction boxes that exceed 100 cubic inches, the National Electrical Code (NEC) requires that the screws used for mounting penetrate the wall a minimum of 1/4 inch. This requirement ensures that the junction box is securely mounted to the wall or structure, providing stability and support for the electrical connections made within it. Proper penetration depth is crucial for maintaining the integrity of the electrical installation, as it helps prevent the junction box from becoming loose over time due to vibrations or other factors.

Understanding the specifications related to mounting junction boxes is vital for ensuring both safety and compliance with electrical codes. Adhering to the 1/4 inch penetration rule helps ensure that the junction box can withstand various conditions while minimizing the risk of electrical hazards associated with loose or improperly mounted boxes.

The other options provided exceed the minimum requirement, but they are not necessary according to the NEC, which specifies 1/4 inch as the adequate depth for this application.