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This nonmetallic box may have originally complied with the Code when it was first installed. Now, with the wood paneling installed over the gypsum wallboard, it’s a violation. Section 314.20 permits installations within or behind noncombustible surfaces such as gypsum wallboards to be set back from the finished surface a maximum depth of ¼ in. This same Code Section requires installations within a surface of wood paneling or other combustible materials to have the box, plaster ring, or box extender installed so it covers all the way to the surface of the wood paneling or combustible material. The installation could even project out beyond the surface of the wood paneling or combustible material. The installation, however, is not permitted to be recessed behind the wood paneling (as shown in this Photo). Any arcing or sparking within the box could allow the sparks to contact the combustible wood paneling, possibly resulting in a dangerous fire. Before installing this receptacle, a listed box extender should have been installed to make this installation Code compliant.