a. There are many types of electrical boxes. They are made of either metallic or nonmetallic (NM) material. The metallic box is still widely used; however, the NM box is becoming more popular because it is less expensive and the installation of conductors is easier and faster than with the metallic box. Figure 1 shows a NM, two-gang box.

b. Electrical boxes come in many shapes, sizes, and depths (Figure 2). Box depths range from 1/2 inch to 6 inches. Boxes of a special size and depth can be ordered.

c. When required, common metallic boxes can be ganged together to make the box wider (Figure 3). Boxes to be ganged must be of the same type and have a removable side. If a box is not deep enough, extension rings can be added to increase the cubic-inch capacity as needed (Figure 4. Extension rings are attached to a box by tightening the screws.

a. Electrical boxes are mounted in several different ways. Some boxes come with the mounting brackets attached. The side-mounting box is attached to a stud with nails or screws (Figure 5).

b. The front-mounting box is attached to a stud by hammering the spikes of the mounting bracket into the stud (Figure 6). This procedure is known as setting the box. Nails and screws are also driven through the mounting bracket to ensure that the box is securely mounted to the stud to prevent movement.

c. An adjustable bar hanger is designed for installation between wall studs, ceiling joists, or floor joists. The bar hanger is nailed or screwed to studs or joists, then a box is mounted to the bar hanger (Figure 7).

d. Electrical boxes must be mounted so that the outer edge of the box will be flush with the finished surface of the wall. Some boxes come with thickness gauges stamped on them (Figures 8 and 9). Align the gauge against the side of the stud (Figure 9). Move the box in or out, depending on the thickness of the proposed finished surface. Nail or screw the box to the stud.

e. Electrical boxes installed in walls constructed of noncombustible material can be mounted up to 1/4 inch back from the finished surface. Electrical boxes mounted in walls containing combustible materials must be mounted flush with the finished surface.

f. All electrical boxes (including junction boxes) should be mounted so that the conductors are accessible. Wall covering should never cover boxes.

g. Electrical switch boxes may be mounted 46 to 52 inches from the top of the box to the finished surface of the floor. Outlet boxes may be mounted 12 to 18 inches from the bottom of the box to the finished surface of the floor.