Understanding Dimmer Switch and  3 Way Switch Wiring

I have a rotary dimmer switch that I am making a regular three way switch  with 12 gauge wiring.

• I have one 12-2 leg from a switch coming to the dimmer, then the dimmer switch has four wires on it; two red, one black, then ground; and then a 12-3 wire coming down which I am traveling to the a normal three way switch and then powering my lighting off that switch.
• Now the wiring for the dimmer switch I don’t know where to wire them to.
  All together in that dimmer I have three black, two red, two neutral, and three ground.

I am confused, can you please help?

This electrical question came from: Andrew, a Handyman from Tower City, Pennsylvania

See more about Home Wiring for Pennsylvania

Dave’s Reply:
Thanks for your electrical question Andrew

Biggest Mistake When Replacing 3 Way Switches
One of the biggest problems that occurs when replacing 3 way switches is when the existing switch is removed before identifying the wiring and taking too many wire connections apart.

Three way switch wiring for a dimmer and a standard 3 way switch is the same except that the dimmer switch has a set of wires and not terminal screws to make up the wiring.

The Key for Comparing 3 Way Switch and 3 Way Dimmer Switch Wiring

There are only three connections for both the 3 way dimmer and the 3 way switch

1. The Power In or Out.
   The Dimmer Power is typically the Black Wire.
   The Switch Terminal is typically the single screw terminal at one end of the switch and is usually a Black Screw
2.  The Two Travelers (or Jockeys-electrician terminology)
   The Dimmer Travelers are typically the two Red Wires.
   The Switch Travelers are typically the two screw terminals at one end of the switch and are usually brass.
3. The Ground Wiring is typically a green insulated wire on the dimmer switch and green or bare copper wire in the switch boxes and they bond together and a pigtail wire is attached to the green ground screw on the 3 way switch frame.

Key Components of 3 way Switch Wiring

• There are several wiring configurations that are used for 3 way switching which include the Power In, the Switched Leg Out to the light fixture(s), the two Travelers and of course the Ground wires.
• There are also other cables that may be found and need to be identified, such as:
  • Power Out to another light fixture switch or wall outlet.
  • Additional cable(s) that may lead to additional light fixtures that are controlled by the three way switching. These cables are most always found in the  same switch box location.
  • Additional Power Cables include a hot, neutral and ground wire.
• NEUTRALS are not used in standard 3 way switching, however it should be understood that WHITE WIRES may be used for the 3 way switching configuration but that does not mean that they are neutral wires, in fact they should be identified with black or red electrical tape when a white wire is used for the purpose of power switching.

When the wiring has been taken apart or the configuration is unknown the electrician should start by using a voltage tester to identify all of the cables with regard to the key connections as described above.

Please Note: These are typical connections for standard 3 way switches. This does not apply to wireless dimmer switches and some Lutron Light Switches.

The Following links will assist you with Wiring 3 Way Switches and Dimmer Switches

For more information about 3 Way Switch Diagram
3 Way Switch Diagram

3 Way Switch Diagram

In response to the requests for this information, I have developed a comprehensive,step-by-step guide designed to walk you through the identification and wiring of your 3-way switches.

How to Wire a Switch

Wiring a Light Switch – Diagram 1

Wiring Diagrams

Fully Explained Light Switch Wiring Diagrams. Detailed Electrical Wiring Diagrams and Pictures assist your Home Electrical Projects.

Wiring a Dimmer Switch

3 Way Dimmer Switch Wiring Diagram

Fully explained 3 way dimmer switch wiring diagram will take the mystery out of wiring a 3-way dimmer switch.

Electrical Wire for the Home

Guide to Home Electrical Wire

Electrical Wire for the Home

Complete listing of electrical wire types and parts used for home projects with electrical code information serves as selection guidelines.

Lighting for the Home

Planning and Installing Home Lighting

Home lighting articles covering recessed lighting, under cabinet lighting, lighting terminology and more.

Using Electrical Testers

Understanding Electrical Testers

When working on home electrical wiring using voltage testers can play an important part in electrical safety. Electrical testers enable you to identify electrical circuits and help prevent the possibility of accidental electrical shock.
Types of Electrical Testers