Switches are made in assorted sizes and shapes and are rated at different voltages and amperages. A single-pole switch is the most commonly used type of switch. Single-pole switches are used to control devices, such as lights or receptacles, from one location (Figure 1-12).
Figure 1-12. Single-pole switch
There are simple rules of thumb, that when followed, make wiring circuits very easy. Here are the rules of thumb for a single-pole switch:
Rule 1: The hot conductor (wire) is the only conductor that is switched. The incoming hot conductor from the power source goes to either terminal on the switch.
Rule 2: The conductor going from the other terminal of the switch goes to the device. This conductor must be black.
Rule 3: The neutral conductor goes to the current-using device (such as a receptacle or a light fixture), and it must be white or neutral gray.
There are two wiring methods that the electrician must know. The first is an "in line," and the second is a "switch loop." If the conductors from the panel box go to the switch then to the light, it is an in-line circuit. Follow the rules of thumb and compare them with Figure 1-13 below.
Figure 1-13. In-line circuit
A switch loop occurs when the conductors go to the light then to the switch. In Figure 1-14 notice that the same rules of thumb were used for both wiring methods.
Figure 1-14. Switch-loop circuit
In the switch loop (Figure 1-14), the incoming black (hot) conductor is spliced to a white conductor (making it a hot conductor) at the light to complete the run to the switch.
When a white conductor is used to carry current to a switch, as in a switch loop, the white conductor must be permanently marked to indicate it is not neutral but is now a hot conductor. This is usually done with black electrician's tape. Place a piece of tape at both ends of the white conductor that is being used as a hot conductor everywhere it is exposed in every box. Do not tape a white conductor that is being used as a neutral conductor.
When an electrical device requires control from two different locations (for example, the top and bottom of stairs), three-way switches are used. Three-way switches must be used in pairs. Three-way switches have three terminals or screws on them and no ON or OFF markings on the handle (Figure 1-15).
Figure 1-15. Three-way switch
A three-way switch has three terminals, one common in brass or black and two travelers in silver, white, or a light-colored metal. If all terminals are the same in appearance, there may be a letter beside the common terminal (Figure 1-16).
Figure 1-16. Three-way switch with three terminals
A three-way switch shift's the electrical path from the common terminal to one of the traveler terminals (Figure 1-17).
Figure 1-17. Three-way switch shifting the electrical path
When installing three-way switches, the silver screws on one three-way switch are wired together with the silver screws on the other three-way switch, using conductors called travelers (Figure 1-18).
Figure 1-18. Traveler conductors
There are four simple rules of thumb for wiring three-way switches. They are
Rule 1: The incoming hot conductor goes to the common terminal on the nearest three-way switch.
Rule 2: The conductor from the common terminal on the other three-way switch goes to the device (light, receptacle). This conductor must be black.
Rule 3: The neutral conductor goes to the device. The neutral conductor must be white or neutral gray.
Rule 4: The traveler terminals on one three-way switch go to the traveler terminals on the other three-way switch.
Wiring a three-way lighting circuit follows the simple rules previously stated. To complete the circuit, one of the switches is operated as shown in Figure 1-19a. In Figure 1-19a, the circuit is open and the light will not burn. In Figure 1-19b, the circuit is complete and the light burns.
Figure 1-19a. Wiring a three-way lighting circuit
Figure 1-19b. Wiring a three-way lighting circuit
Look at Figure 1-20 and follow the rules to wire a three-way switch system.
Figure 1-20. Wiring a three-way switch system
A four-way switch is similar to a three-way switch. Neither switch has ON and OFF markings. The four-way switch has four terminal screws and no special markings. A four-way switch is used with two three-way switches to control electrical equipment from three or more locations. Each additional four-way switch will give one additional control point (Figure 1-21).
Figure 1-21. Four-way switch
A four-way switch controls the two traveler conductors by switching the electrical flow through one terminal or the other (Figure 1-22).
Figure 1-22. Wiring a four-way switch
Follow the current flow in Figures 1-22, positions 1 and 2. You will notice that the circuit is complete in both and the light is on. Simply changing the switch position of any of the three switches will cause the light to go off. Change any switch position a second time, and it will turn the light back on.
A double-thrown switch is used when two conductors must be open at the same time. Double-thrown switches are used primarily in 240-volt lines; however, they are occasionally used when the hot and neutral conductors must be disconnected from the device. Double-thrown switches look just like four-way switches, but they have ON and OFF markings (Figure 1-23).
Figure 1-23. Double-thrown switch controlling a duplex receptacle
Duplex switches have two switches mounted on a single frame. Duplex switches are used to control two separate electrical devices from a single location (Figure 1-24).
Figure 1-24. Duplex switch
A switch can also be used to control a receptacle. It is common to wire a duplex receptacle where half the receptacle is controlled by a switch and the other half has power all the time. This type of circuit is called "split wired." Split-wired receptacles are covered in Lesson 2.
A switch-receptacle combination may be wired two ways: the switch controls the outlet, or the switch controls a light and the outlet is always hot (Figure 1-25).
Figure 1-25. Switch-receptacle combination
General-use snap switches rated for alternating current (AC) only can be used for control of resistive and inductive loads. Check the load rating of the switch. Do not overload it. A switch will not carry more than its rated voltage.
Motors require additional amperage until the rotation speed is achieved. For this reason, motor loads should not exceed 80 percent of the ampere (amp) rating of the switch at its rated voltage. For example, a switch rated at 120 volts and 20 amps can only carry a 16-amp motor load.
|Content provider: U.S. Army, David L. Heiserman
Publisher: SweetHaven Publishing Services
Copyright © 2005, SweetHaven
Revised: April 19, 2005