Light Switches, Dimmers and Timer Switches

Single-pole, three-way, dimmer or timer?

A single-pole switch controls a light from one place; a three-way pair controls it from two, such as at the top and bottom of stairs. Check the terminals before buying: a single-pole has two brass terminals plus ground, while a three-way has a darker common screw. Dimmers add a load rating and a control type, and rotary dials are a common style. Timer switches turn a load off after a set time, useful for fans and lights left on by mistake.

LED and compact fluorescent bulbs need a dimmer rated for them, and bulbs must be marked dimmable, or they may flicker, buzz or fail early. Dimmers also have a minimum and maximum load in watts. Fan speed controls are separate devices made for motor loads, so use one of those for a fan and keep dimmers for lights. Photo controls switch a load on at dusk and sit in a receptacle or wall box with a stated voltage range.

Volts, amps and the 22 mm or 30 mm cutout

Every switch lists voltage and current: household devices are usually 15 A at 120 V, and heavier or commercial devices list 20 A or 277 V. Industrial pushbuttons, selector switches and indicator lights are sold by panel-hole size, most often 22 mm and 30 mm, and their contact blocks list a type such as 1NO/1NC with amps at 240 V. Colors carry meaning in control panels: red for stop, green for start. Pick the panel hole before the color.

Questions about Light Switches, Dimmers and Timer Switches

Will any dimmer work with LED bulbs?

No. Use a dimmer marked for LEDs and bulbs marked dimmable, and keep the total load within the dimmer's minimum and maximum. An old incandescent dimmer can cause flicker, buzzing or a narrow dimming range with LEDs.

How can I tell a three-way switch from a single-pole?

Look at the terminals. A single-pole has two terminals and usually ON and OFF marked on the toggle; a three-way has three terminals, with one darker common screw, and no ON or OFF marking. Turn off the breaker and label the wires before removing the old switch.

What does 22 mm mean on a pushbutton or indicator light?

It is the diameter of the hole in the panel that the device mounts through. Standard industrial pushbuttons use 22 mm, and larger heavy-duty ones use 30 mm. Check the hole size, the mounting depth behind the panel and the thickness it can clamp.