The simplest and most common light switch is actually referred to by hardware dealers and electricians as a “single-pole light switch.” With a single-pole light switch, flipping the lever up completes the circuit, turning lights or appliances on, and flipping it down breaks the circuit, turning lights or receptacles off.
A single-pole switch has two brass terminal screws on the side that receive the black (“hot”) wires of the circuit. One black wire comes from the power source and the other goes to the light(s).
When you turn the switch off, it interrupts the electricity that flows through the black wire from the power source to the fixture. For this reason, the two main terminals are connected to black wires. The bare ground wire—if there is one— is connected to the green grounding screw on the switch.
The wiring diagrams on this page can help you plan the proper way to wire for a light switch. Always turn off the power to the circuit before working on wiring. See How to Turn Off Your Home’s Electricity.
Again…the circuit’s white wires bypass the switch UNLESS…a white wire has been converted to do the job of a black wire. Many homes are wired with 3-wire non-metallic cable (such as the brand Romex®) that consists of one black wire, one white wire, and one bare or green grounding wire.
When wiring switches, this type of cable may be used as a switch leg—where you need two black wires to go from the switch to black wires located at the light or at an intermediate electrical box.
As shown in the diagrams below, you can paint a couple of inches of the end of the white wire black—or wrap it with black electrical tape—to indicate that it is being used as a black wire. Electrical codes can vary on this practice.
Single-Pole Switch Wiring Diagrams
The right way to wire a single-pole switch depends upon where the switch is located relative to the light. The diagrams below show the various options.
A dimmer switch is wired the same way as a single-pole switch. In this illustration, you can see the red hot “lead” wires of the dimmer are connected to the inbound black wire from the electrical source (the electrical panel) and the black wire that goes to the light fixture’s black wire which, in this case, is a white wire that has been taped with black electrical tape.
The type of switch that will operate hallway lights from either end of the hallway is called a three-way switch; it has an extra terminal. For information about the different ways to wire this type of switch, please see How to Wire Three-Way Switches.