The single-pole, wall-mounted toggle switch, as shown in below Figure , is the most commonly used switch in homes and offices. These wall switch wiring diagrams have the two brass screw terminals on the right side of the switch for the connection of black “hot” wires. It makes no difference which “hot” wire (input or output) goes to which brass screw, but most electricians follow a consistent pattern when wiring them into branch circuits so that input wires can be distinguished from output wires. It was explained previously that single-pole toggle switches are the only wall-mounted switches with ON and OFF legends marked on their toggles. If the switch is mounted correctly, ON is visible when the load is powered. Single-pole toggle switches for use in nonmetallic switch boxes have a grounding screw, typically on the left side of the switch.
Neither the three-way switch shown in above Figure (b) . nor the four-way switch shown in above Figure (c) has the ON/OFF toggle legends because they would have no meaning; the positions of the toggles on the other switches in the three- and four-way circuits determine the ON and OFF positions of any one switch in the circuit.
Each three-way switch has three screw terminals (one painted to identify it as “common”) and an internal movable blade. In wiring three-way circuits, common traveler wire is connected between one of the brass terminal screws on each switch. A lamp in a three-way circuit is OFF when one switch toggle is upand the other one is down.By flipping one toggle of the pair so that both are either up or down, the circuit is completed and the lamp will turn on.
LAMP CONTROLLED BY A SWITCH
below Figure illustrates a lamp controlled by a single-pole switch. The black input “hot” wire goes to the upper brass screw, power passes through the switch, and the black output “hot” wire goes from the lower brass screw to the lampholder. The neutral wires bypass the switch and go directly to the lampholder. With the switch between the “hot” wires, the lamp circuit can be made or broken. A switch in the neutral wire could make or break the circuit, but it would not disconnect the lamp from the power source. This cheme could expose a person to electrical shock, or a short circuit could occur at the lamp with the switch off.
LAMP CONTROLLED BY A SWITCH LOOP
below Figure illustrates a switch loop for wall switch wiring diagrams. The NEC limits the number of wires allowed in a switch box. To avoid this limit, circuit wires can be run to the lampholder first with a switch loop going to the switch, as shown. The black “hot” input wire and its black-marked extension go to the lower brass screw on the switch. Power passes through the switch and leaves from the upper brass screw on a black wire that goes to the lampholder. The white neutral wire bypasses the switch and goes directly to the lampholder.
LAMPS AT THE ENDS OF CIRCUITS
below Figure illustrates a circuit ending at a lampholder for wall switch wiring diagrams controlled by a single-pole pull-chain switch.The black “hot” and white neutral wires go directly to the lampholder. This wiring scheme is frequently used in unfinished attics and basements.
below Figure illustrates another example of circuit ending at a lampholder, but this circuit is controlled by a single-pole switch. The “hot” wire connects the black-marked white extension to the lower brass screw of the switch. Power passes through the switch and leaves from the upper brass screw on a black wire to the lampholder. Again, the white neutral wire bypasses the switch and goes directly to the lampholder. This wiring scheme is widely used in finished room
SWITCH IN THE MIDDLE OF A CIRCUIT
below Figure illustrates a single-pole switch in a middle of a circuit controlling a lamp at the end. The “hot” black wire is attached to the lower brass screw. The power passes through the switch and goes from the upper brass screw on a black wire to the lampholder. Again, the white neutral wire bypasses the switch and goes directly to the lampholder.
LAMP IN THE MIDDLE OF A CIRCUIT
below Figure illustrates a single-pole switch at the end of a circuit controlling a lamp in
the middle of the circuit. This circuit is wired as in the switch loop of Fig. 7-3. The black “hot” input wire and its black-marked extension go to the lower brass screw on the switch. Power passes through the switch to the upper brass screw and a black output wire that goes to the lampholder. The white neutral wire bypasses the switch and goes directly to the lampholder. In this circuit, two or more cables can enter the octagonal fixture box and the “hot” and neutral wires go to the next outlet
LAMP IN THE MIDDLE OF A CIRCUIT CONTROLLED BY THREE-WAY SWITCHES
below Figure illustrates how a pair of three-way switches can control a lamp in the middle of the circuit from two different locations. This circuit allows the lamp to be switched on from either the top or bottom of a stairway, or from either end of a hallway. It can be switched off by the second switch. Each three-way switch has three screw terminals, one painted to identify it as “common” and the other two interchangeable as traveler or return terminals. The three-way switch also contains a movable blade.
The “hot” black wire goes to the common terminal on the lower three-way switch. After power passes through the switch, it leaves by the upper common terminal through a black-marked white wire to the upper common terminal of the upper three-way switch. Again, power passes through that switch to the common terminal to a third black “hot” wire that takes it to the lampholder. The white neutral wire bypasses the lower switch and goes directly to the lampholder. The common red traveler wire connects the two screws not functioning as “common.” As stated earlier, a lamp in a three-way circuit will be on only when both switch toggles are in the same positions, either up or down.