Since you must never interrupt or switch the neutral wire, a switch is connected in series only with the circuit’s hot wire. (Receptacles are connected to both the hot and neutral wires of a circuit.) Connections made using wire-binding screws are more secure than those with push-in connections.
The most common type of wall switch, the single- pole switch, controls a receptacle outlet or fixture from one location. It has two brass-colored terminal screws and its toggle is marked On and Off. Used in pairs to control a fixture from two locations, a three- way switch has two brass-colored traveler terminals for the wires between the two switches and a dark com mon terminal, which connects the incoming hot wire or the switched wire up to the fixture. The toggle on a three-way switch has no On or Off markings.
Switches in the United States are now required to be grounded and have green grounding screws. Replacement switches must have the same voltage and amperage ratings. Note: Standard dimmer switches shouldn't be used for ceiling-fan control.
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Reading a Switch
There’s a lot of information on the front and back of a typical snap switch. Markings include voltage and amperage ratings, wire material (CU means copper), third-party certification and the size of wires that may be terminated. Electricians normally use screw terminals, not the less reliable push-in terminals.
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Replacing a Single-pole Switch
Use a noncontact voltage sniffer to make sure power is off. Remove switch cover plate and switch. Disconnect wires from the old switch and reconnect to new switch. Install a pigtail from grounding screw on switch to grounding wires or metal box. Tighten screw terminals and fold wires and switch into box. Screw switch to box and reinstall cover plate. Restore power and test the switch.
A middle-of-circuit switch has two black
wires attached to the brass screws. One black wire is the incoming hot wire.
The other black wire is the switch-leg to the light fixture.
In a switch-loop circuit using two- wire
NM cable, the incoming hot wire is white, re-identified with black tape.
The other black wire is the switch-leg to the light fixture.
Installing a Dimmer Switch
Dimmer styles include rotary, slider, toggle and dig ital electronic types for controlling incandescent, low-voltage and fluorescent lighting (fixture modification may be required). Some dimmers replace single-pole switches for controlling lights from one location; other special dimmers replace three-way switches for multiple location control. To avoid electrical accidents and risk of fire, make sure dimmer-switch ratings match the load and type of light and that electrical boxes are big enough to accommodate the larger wires and wire connectors. Dimmers are required by code to be grounded.
1. Pull switch out and turn power on. Check for voltage between box and each terminal. If tester lights, box is grounded. Turn off power to proceed.
2. Press grounding clip and 6-in. (15-cm) length of bare copper wire onto box’s edge using a screwdriver. Notch drywall to provide clearance for clip.
3. Select proper connector based on wire sizes. Hold stranded wire 1/8 in. (3 mm) beyond solid wire and twist wire connector clockwise until it's snug.