Calculations for a Masonry Wall Box

Depth

• Depth dimensions describe the distance between the front face and back plate of a masonry wall box. These boxes measure at least 2 inches deep. Any wall box must exhibit enough depth to fit the outlet intended for it and the electrical wiring that connects to that outlet. The depth of the box ideal for your specific masonry wall depends on the thickness of your wall. For instance, manufacturing firm Garvin Industries recommends its 3.5-inch-deep wall boxes for masonry walls with a thickness of 6 to 8 inches and its 2.5-inch-deep boxes for walls with a thickness of 4 inches.

Height and Width

• Height and width dimensions help you determine how large a hole you must cut in your wall to fit a wall box. Width depends on something called “gang,” which describes how many outlet pairs you need. A one-gang wall box, for instance, fits one vertically oriented pair of outlets, while a two-gang wall box fits two vertically oriented pairs of outlets, side by side. Height dimensions are more standardized, in the 4- to 4.5-inch range. These wall boxes all fit standard outlet pairs.

Faceplate

• A faceplate fits over the open front of a wall box. It provides an aesthetically appealing cover for these usually very bland, steel-colored boxes and helps protect you and your family and pets from the dangers from exposed electrical wiring. A number of manufacturers provide faceplates with masonry wall boxes, or sell faceplates designed for their own boxes. A faceplate should contain holes for access to your outlets and screws. Always use a faceplate with the same width and height dimensions of your wall box and make sure that the holes in the faceplate line up with the appropriate features of your wall box. Taking simple measurements can ensure this.

Holes

• All wall boxes contain at least two holes, one at the back and one on the top or sides. The hole at the back allows you to feed electrical wiring into the box. The hole at the top or sides allows you to connect the wall box to a mounting device that ensures your box doesn’t slip and fall into the wall. When installing a mounting box, you must cut a hole in the wall. The easiest way to ensure cutting the right size hole entails measuring the outside of your box, drawing an outline on the wall to these specific dimensions and cutting a hole to that size. You need a heavy-duty tool like a power saw for cutting in masonry material.

Materials

• Wall box dimensions ultimately depend on considerations such as the thickness of walls and the height and width of outlets. The materials of a wall box are what make it specifically suited to use with masonry walls. Masonry walls contain abrasive material such as concrete and brick. Your wall box must offer resistance to these materials, while providing an appropriate substitute in terms of weight support. Because of this, all manufacturers make masonry wall boxes from metal, usually steel. Some steel wall boxes contain additional elements, like polyvinyl chloride (PVC) coating or rim work, for additional support and protection.