Basic Principles Of Light Switches

by Darwin Hall

light switch

All switches may look similar, but they have significant distinctions.  Furthermore, identical switches are wired differently in different situations.

The main distinction is the number of switches controlling a particular light or group of lights, and whether wiring from the electricity source goes first to the switch or to the fixture.

In spite of all the variations in style and the addition of certain features on some switches, there are really only four basic types, and only two are generally used in residential wiring.

Basic principles of switching.  There are many configurations for wiring connections involving two-way, three-way, and four-way switches.  It is important to understand connection principles than to memorize the hook-ups.  This way you will be able to adapt to any installation.

The most important principle is that a neutral wire is never switched.  A switch interrupts the flow of current to a fixture, never from it.  The path of the current is always the same: from the source to the switch(es) to the fixture and then back to the source.  All wires leading to the fixture are hot; all wires returning from the fixture to the source are neutral.  If you are wiring with cable, remember that a cable is a cluster of indivual wires that serve different functions.

Wires should be color coded properly.  If you are wiring with cable, there are times when you may need to use the white wire as a hot conductor.  In such cases, always blacken both ends of the white wire to indicate that it is hot.  Use electrician’s tape or paint.  Use switches with the correct terminals and cable with the appropriate number of conductors.

3 way switch

Example of a 3-way switch: source through fixture

The switch-fixture connections are only part of larger circuits; the boxes may also be junction boxes for extending the circuit in other directions.

There may be other wires in the same box you are working in, so always be aware of their function.

Types of switches

Single pole.  Use a two-way, or single-pole, switch as the only switch operating a fixture.  A single-pole switch has on-off markings on the toggle and two terminals (besides ground).

Double pole.  Use for 240-volt equipment or to operate two circuits at the same time.  Has on-off markings and four terminals.

Three way.  Use in pairs, when two switches control the same fixture.  The toggle can be on or off in either position.  Has three terminals.

Four way.  Use with two 3-way switches when three switches control the same fixture.  Toggle is on or off in either position.  Has four terminals.

Wiring Switches

Connect wires to a switch using screw terminals.  Strip 5/8-inch insulation from the wire, loop the bare end around the screw clockwise, and tighten the screw.  Always loop the wire around the Watch the Videoscrew clockwise.  Another method is to connect terminals by pushing the bare end of the wire into the designated hole in the back of the switch.

Use the wire gauge on the switch to strip the end of the wire to length.  Be sure to connect the correct wire to the correct screw and terminal:

  • Black wire to brass-colored screw
  • White wire to silver-colored screw
  • Green wire to green or dark-colored screw
  • Bare wire to box (ground)
  • Red wire to brass-colored screw.

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