FINISH WORK Once you begin the finish work, the first thing you need to do is to make all ground connections. Equipment grounding is the grounding of all exposed noncurrent-carrying metal parts of an electrical system to the earth. Grounding is done to protect anyone who might come in contact with these parts from being shocked and also to protect equipment from damage. Grounding is accomplished when all noncurrent-carrying parts are connected to a grounding conductor (or grounding has been achieved by other means, as approved by the NEC(c)), and the grounding conductor has been connected to earth at the service equipment or panelboard, as shown in figure 5-29. The equipment

Figure 5-28.- Nonmetallic cable installation.

Figure 5-29.- Duplex receptacle electrical connection with the grounding system. ground does not normally carry current. The only time it does is when there is a fault in the circuit. At all outlet boxes that require grounding according to the NEC(c), the equipment-grounding conductor must be fastened to the box with either a grounding clip or a grounding screw, as shown in figure 5-30.

When we speak of installing a device, we should be aware that, according to the NEC(c), a device is the part of an electrical system that is intended to carry, but not use, electrical energy; for example, switches and receptacles are devices. The grounded duplex receptacle comes equipped with a green hex-head screw to be used for connecting the ground wire. When more than one receptacle is connected in a circuit, the NEC(c) requires that these receptacles be connected to the grounding wire in such a way that the continuity of the circuit equipment ground is not broken if the receptacle is removed This grounding method is accomplished as

Figure 5-30.- Grounding clip and grounding screw.

Figure 5-31.- Grounding methods: (A) More than one receptacle in line and (B) a single receptacle in a circuit. shown in figure 5-31, view A. Figure 5-31, view B, shows an example of how you can ground a single receptacle in a circuit using a grounding clip.

Grounding the receptacle in this way bonds the box, grounding wire, and receptacle, and precludes use of an additional jumper wire. Now that we have made the ground connections, the next step of the finish work is to make terminal connections. Properly made terminal connections are important for several reasons. The operation of the circuit, prevention of tire, and safety of personnel all depend on good electrical connections. Electrical connections must be electrically and mechanically secure. There are two ways to make connections to devices: with or without using a terminal loop. The method of using the terminal loop and screw is shown in figure 5-32. Some receptacles and switches are made so

Figure 5-32.- Wire terminal loop.

that they can be wired from the back without using a terminal loop. This method is shown in figure 5-33. Now that you have made your terminal connections,

you install the device into its box and secure it with the screws provided. The next step is to install the receptacle cover plates. Cover plates will be installed plumb, will completely cover the opening, and will be seated against the mounting surface. When installing switches for interior wiring, you use single-pole, three-way, or four-way toggle switches. Most of the switches you use will be single-pole, but occasionally you will have to install a three-way

system, and on rare occasions, a four-way system. Still another system of switching, called the low-voltage system, is coming into use.

Figure 5-33.- Back-wired receptacle.

Figure 5-34.- Single-pole switch circuit. A single-pole switch is a one-blade, on-and-off switch that may be installed singly or in multiples of two or more in the same metal box. In wiring a single-pole switch, a general rule is a neutral conductor (white wire) should not be switched or used as one leg in a switch loop. This rule is easily followed in conduit systems but does not apply to armored and nonmetallic sheathed cable. Article 200-7 of the NEC(c) contains the exception to this rule. Figure 5-34 shows a single-pole switch circuit using nonmetallic sheathed cable. In a three-way switch circuit, you may turn a light on or off from either of two positions. The typical situation is one in which one switch is at the head of a stairway and the other at the foot. Figure 5-35 shows how the circuit functions.

Figure 5-35.- Three-way switch circuit.

Terminals A and A' are the common terminals, and switch operation connects them either to B or C and B' or C', respectively. Either switch will operate to close or open the circuit, turning the lights on or off.

By tracing the circuit in figure 5-35 from the source, you can see that the hot wire goes to the first switch, through the closed switch blade to the other switch by way of the traveler, and through the closed switch blade to the other switch by way of the traveler, and through this switch to the light. If the position of either of the switches is changed, the circuit is broken.

One or more four-way switches may be used with two three-way switches to provide control of a lamp from three or more different points. A four-way switch is an extension of a three-way circuit by the addition of a four-way switch in series with the two traveler wires.

Figure 5-36, view A, shows how a four-way switch is used in combination with two three-way switches to control a lamp from three locations. By tracing this circuit from the source, you observe the hot wire connected to Switch C passing through Position 1, which is closed. The hot wire continues to Point 4 on the four-way switch (B). At this time the toggle on Switch B is in the UP position, and contact is made from Point 4 to Point 3. The hot wire continues on through the

traveler to Switch A, and through Position 2 (which is closed) to the light.

Figure 5-36.- Four-way switch circuit.

Suppose, now, that you want to turn the light off at the four-way switch (B). By putting the toggle in the OFF (down) position, you change the switch blades from Points 1 to 2 and 3 to 4 to Points 1 to 4 and 2 to 3. (See fig. 5-36, view B.) If you now retrace the circuit from Switch B to Switch A, you will find that it goes from Point 4 to Point 1 on Switch B and through the traveler to Switch A to Point 1 where the circuit is broken by the blade being in the open position.

Note that three-and four-way switches may be used as single-pole switches, and four-way switches may be used as three-way switches. However, three-and four-way switches are usually larger than single-pole switches and take up more box room. The size of a switch depends on its ampacity (rated maximum amperage). The ampacity and maximum allowable voltage are stamped on the switch and must be considered when you order equipment for the job.