NEC Commercial Electrical Practice Test

What is the maximum depth an electrical box can be set back from the finished surface of walls or ceilings made of non-combustible material?

1. 1 inch

2. 1/2 inch

3. 1/4 inch

4. 3/8 inch

The correct answer is: 1/4 inch

The maximum depth an electrical box can be set back from the finished surface of walls or ceilings made of non-combustible material is 1/4 inch. This standard ensures that the cover plate for the electrical box can be securely fastened and that the electrical connections are accessible for maintenance and safety. Setting the box back too far from the finished surface could result in complications, such as difficulties in securing the cover plate, which could ultimately lead to exposure of the electrical connections. Additionally, maintaining the 1/4 inch requirement helps ensure compliance with safety codes that protect both the integrity of the installation and the safety of the building's occupants. When adjusting installations to comply with the NEC, it’s crucial to adhere to these guidelines to prevent electrical hazards and ensure proper functionality of electrical devices. This specific depth requirement reflects an understanding of safe and practical installation practices.