The setback distance of a device box face from the finished surface is determined by the finish type. For gypsum wallboard, what is the maximum setback?

• A. 3 mm (1/8 in)
• B. 6 mm (1/4 in)
• C. 9 mm (3/8 in)
• D. 12 mm (1/2 in)

Answer: (B)

The main idea is how far the device box face can be recessed behind the finished wall to accommodate the wall finish. With gypsum wallboard, the finish adds a relatively thin, consistent layer (tape, mud, and paint). To keep the device face properly aligned with the final surface after finishing, the maximum allowable setback is 6 mm (1/4 inch). Going deeper would cause the face to sit too far back once the drywall finish is applied, while staying within this limit helps ensure the cover fits correctly and the device remains accessible.