Installation of Nonmetallic Cable

Many rooms require multiple ceiling lights. If only two lights are involved, measure half the length of the room and then run diagonals for each half, as shown in figure 5-21, view C. This measurement procedure gives you the location for each light. A room that is to be lit with a row of lights will have them installed along the center line. The lights should be spaced so that the lighting is as uniform as possible. You can determine the spacing by dividing the length of the room by the number of lights. This figure is the space that is to be left between any two adjacent lights. The light at each end of the row is placed at half the preceding distance from the wall. This spacing is shown in figure 5-21, view D. If you take another look at view C, you will see that the space from the end walls to the lights is also half that of the space between the lights. INSTALLATION OF NONMETALLIC CABLE Installation of electrical circuits with nonmetallic cable is fairly simple. It is usually done in two stages. The two stages are called roughing in and finish work. Roughing in is the work done before the walls and ceilings are put in place, and finish work is just what it implies, the finishing up. You splice wires as needed and install the receptacle outlets, switches, and lighting fixtures. ROUGHING IN The main objectives in roughing in are to get circuits routed properly, to reduce the chance of damage to the cable during installation, and to reduce the chance of damage while the structure is being finished or during Figure 5-22.—Nonmetallic cable staples. later modifications. You should refer to Article 300 NEC© for wiring methods. When roughing in your circuits, study your electrical blueprints. They will show the general location of the outlets and switches and how the cable is to be routed. The exact spot where each outlet and switch are to be put is determined by the requirements of the NEC© and the experience of you, the electrician, unless specific directions are given. A straight line is the shortest distance between two points. This principle is used a great deal of the time by electricians when they are routing cables. Cable is run from box to box by the shortest route unless there is a good reason not to do this. Such routing does not always look neat, but it keeps the cost of material and labor down, and since most wiring is concealed, it is not often seen. Cable must be fastened in place to support it and to prevent strain at boxes and connections. Cable must be anchored within 12 inches of a box, cabinet, or fitting and at points no more than 4 1/2 feet apart between boxes. NM cable is usually attached to wooden framing studs by staples (fig. 5-22). Care must be taken not to drive the staples in tight enough to damage the cable. Another method for securing Romex is by the use of straps. Figure 5-23 shows four types of straps that may be used to secure cables. Concealed cable is installed either through holes bored in wooden framing studs or into notches cut in their edges. Holes can be bored with various sixes of bits, depending upon the size of hole needed. The holes should be drilled in the center of framing studs in a straight line and at the least possible angle either Figure 5-23.—Straps for fastening cable. 5-13