How to Extend the Wiring from a 3-Way Switch

By Dave Rongey - Summary:

The Key to Understanding Light Switch Wiring and Knowing What You Can and Cannot Do

White Wires and Light Switch Wiring

Electrical Question: I am trying to figure out how to finish my circuit. I have a 3 way switch controlling a light(in the middle) where the power(2wire) comes into the first gang box that has the leg going out to the light there. The other switch(on the other side of the room)has been wired to control this light as well using 3 wire. (The white coded as black). Using a double gang box for this second box, I’m trying to add an additional single pole switch and continue power to control another light, but I don’t know where this light’s white return wire should connect to, because the white in the box is coded for hot (black).

This electrical question came from: Jeff, from Richmond, Virginia
See more about Home Wiring for Virginia

Dave’s Reply:
Thanks for your electrical question Jeff

Understanding Light Switch Wiring

Understanding how a White Wire is used for light switches can be very confusing, and here is why:

  • Just because you see a “White Wire” in a switch box does not necessarily mean that it is a “Neutral Wire”.
  • It is often found that the White Wire is actually used for switching the hot, thereby being part of what is known as a “Switched Leg” which is nothing more than switching the hot side of the light circuit.
  • In years past and before the days of DIY home wiring, the white wire was used for switching and was not identified with black tape or a black marker which is now required. This was fine for us electricians because we understood this principle.
  • To complicate the issue, seasoned electricians know that long ago the neutral wire was used for switching light fixtures, not the hot wire. This practice was discontinued but every once and a while we still find this in some older homes, especially where there is knob and tube wiring.

The Key to Understanding Light Switch Wiring

  • What you can and cannot do will be based entirely on how the lighting circuit is wired and where the “Neutral Wire” actually is.
  • If you have not installed the electrical wiring then this is best discovered by using a voltage tester.
  • Once you have identified the location of the neutral wire you will then know if and how the wiring may be extended to accomplish your desired extension of the circuit wiring , or if it is even possible due to finished walls or available access.

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