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Old 07-23-2011, 10:45 PM   #1
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3way switch wiring


I'm new to the site, did a search and couldn't find and answer to my question. I recently bought a house, the light going to the basement only has a switch at the top of the stairs, and I would like to add a switch at the bottom of the stairs. In the switch box there are 2 sets of wires. The whites and grounds are tied together and the blacks are screwed to the switch terminals. So I'm guessing the power comes into the switch box and then goes to the light. What would be the best way to add the switch at the bottom of the stairs, if it can be done.
Thanks for any help.

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Old 07-24-2011, 05:07 AM   #2
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3way switch wiring


It can be done. You'll need to run a 3 wire cable between the old switchbox and the new switchbox. (Red, Black, white, bare ground). and buy two 3 way switches. (three terminal screws on each)

-Leave neutral wires as is
-In old switchbox connect power to switch screw marked "common" (usually a different color than the other two)
-connect black wire from light to black wire from new 3 wire cable.
- Connect red and white from new 3 wire cable to the other two terminal screws on the switch.

In the new switchbox,

-connect black to the common screw
- Connect red and white to the other two screws.

Also don't forget to tie the grounds together in the old box as well as grounding the new box.

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Old 07-24-2011, 09:00 AM   #3
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3way switch wiring


If it is a single gang box, you will most likely exceed the box fill by adding a third (3 wire) cable. You may have to replace the existing box with a 22 cubic inch box.

If the boxes are plastic, they do not have to be grounded.

In the existing switch box it does not mater which of the black wires you connect to the switch are connected to the common terminal of the new 3 way switch.
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Old 07-24-2011, 11:34 AM   #4
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3way switch wiring


If the basement is finished you will need to run 4 conductor cable to meet new NEC code.
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Old 07-24-2011, 11:47 AM   #5
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3way switch wiring


It is a finished basement! So how would I connect the 4 cable wires?
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Old 07-24-2011, 11:49 AM   #6
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3way switch wiring


Quote:
Originally Posted by hayewe farm View Post
If the basement is finished you will need to run 4 conductor cable to meet new NEC code.
Clarification: Prior to the 2011 NEC you did not need the neutral.
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Answers based on the National Electrical Code. Local amendments may apply. Check with your local building officials.
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Old 07-24-2011, 12:18 PM   #7
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3way switch wiring


Very few areas have adopted the 2011 NEC that requires a neutral in all switch boxes. The OP does not say whwere he is located but if it is not 2011 NEC it would not require a neutral (4 wire cable). To the OP, If you are required to supply a neutral to the new switch box, the white neutral would connect to the bundled neutrals in the old switch box and be capped off in the new.
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Old 07-24-2011, 12:23 PM   #8
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3way switch wiring


I am in Southern Illinois. I guess I will play it safe and go with the new code. Thanks!
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Old 07-24-2011, 12:30 PM   #9
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3way switch wiring


Quote:
Originally Posted by Mlwhite View Post
I am in Southern Illinois. I guess I will play it safe and go with the new code. Thanks!
Illinois: There is no statewide adoption of the NEC. The following local jurisdictions have adopted the 2008 NEC: Bloomington, Danville, Decatur, Glenn Ellyn, Normal, Rock Island, State of Illinois Capital Development, Washington.

It's your money, but you will have to go to an electrical supply house to get the 4 conductor cable, no big box I am aware of carries it. Make sure you get 14-4 (or 12-4) not 14-2-2 (or 12-2-2). Same number of conductors but different colors and different uses.
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Old 07-24-2011, 07:18 PM   #10
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3way switch wiring


Actually 12-2-2 and 14-2-2 an be used there is not restriction in code to prevent it. Generally the 2-2 cables have a white and a white with red strip. One can be re-designated.

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