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(c) 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(c) 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.

Figure 5-24.- Drilling holes for nonmetallic cable. vertically or horizontally, as shown in figure 5-24. Holes that are drilled in a crooked line or at much of an angle to the line of pull, as shown at the bottom of figure 5-24, make it harder to thread the cable through the holes and pull it into position.

Cable can be placed into notches cut in the edge of the framing members and studs, as shown in figure 5-25, if the notches will not weaken the building structure. The notches should be as small as possible. Their depth must not exceed one fifth of the width of the wood. Cable placed in notches or through studs is protected from nails and screws by a thin metal plate at least one-sixteenth inch thick, according to the NEC(c), Article 300-4, like those in figure 5-25.

Figure 5-25.- Nonmetallic able installed in notches.

Cable is installed through metal framing members in about the same way as it is in wooden ones. Either holes or slots are used and they must be cut, punched, or drilled at the factory or in the field. Normally, holes in metal members must have bushings or grommets inserted securely to prevent damage to the cable covering. If holes or slots have been formed so that no metal edge can cut or tear the cable insulation, bushings or grommets are not needed. Use good judgment when deciding whether or not grommets are required. A steel sleeve, plate, or clip must be installed for protection wherever a cable might be punctured or cut by a nail or screw. The first step in wiring a building after the distribution panel or panels have been installed is, in most cases, to mark the location of the outlet boxes. Then mount the boxes in place unless the mounting of a box might interfere with hole boring or cable anchoring. Once the boxes are in place, make the needed holes or notches for the installation of the cable. Install the cable by starting at the free end. Strip, as a minimum, 6 inches of the outside covering from the cable end. If the box has cable clamps, remove one of the knockouts and insert the stripped cable end through the hole under the clamp until one-fourth inch of the cable cover extends beyond the clamp. Tighten the clamp to hold the cable firmly in place, but be careful not to overtighten as this procedure

Figure 5-26.- Cable termination at box.

could cause a short. This procedure will give you conductor ends 6 inches long in the box, as shown in figure 5-26. You need these ends so you can make splices or attach devices or fixtures easily. Remember to anchor the cable within 12 inches of the box, as shown in figure 5-26. Boxes without cable clamps require a little different procedure. After stripping the cable end, remove one of the box knockouts. Then install a cable connector, similar to the ones in figure 5-27, in the knockout hole. Install the locknut so that it points inward to dig firmly into the metal box as shown in figure 5-27. Put the cable end through the connector to expose one-fourth inch of the outer cover, and then fasten it in place, as shown in figure 5-25. After the free end of the cable is in the box, work the cable back toward the other box. Run the cable along the framing members, fastening it at points no more than 4 1/ 2 feet apart. When you get to the other box, cut the cable to length, allowing for 6 inches of free conductor in the box. Strip the outside covering, insert the cable end, fasten it to the box, and anchor it within 12 inches of the box. To help avoid damage to the wires as wall coverings are being placed and other construction is being done, make sure you tuck back the wires into the outlet box.

Figure 5-27.- Nonmetallic cable box connectors and mounting techniques.

Look at figure 5-28. As you can see, most of these cables are run through holes in the framing members. When holes are involved, you must plan ahead for easiest installation and the least waste. You would find it to be a little easier to run the cable between the two duplex receptacle boxes in the figure if you put a carton of cable near the box on the right and thread it through the holes to the box on the left. For the circuits that run from the left duplex receptacle box and the switch box to the ceiling outlet, the carton of cable should be placed under the boxes. Then you thread the cable up through the holes to the ceiling outlet. From these examples, you can see that you need to look at what is involved before you start to run the cable for a circuit. After you have completed the roughing-in phase of a project, your job comes to a halt for a time. In most cases, you should not start the finish work until the walls and ceilings are completed; after which you can splice wires as needed and install the receptacles, outlets, switches, lighting fixtures, and covers.