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I'm replacing (yet again) my bathroom dimmer switch. The old switch had 3 wires: 2 black and one green. The two black wires were attached to the wires coming out of the wall and the green wire was attached to nothing. The new switch has 4 wires: black, red, red/white striped, and green. Can I attach the new switch somehow? If not, what would you recommend when I only have 2 wires (circa 1930) coming out of the wall (besides rewiring my house)?

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    Did you read the installation instructions? – Tester101 Sep 10 '14 at 23:11
  • What is the make and model of the dimmer? – Tester101 Sep 10 '14 at 23:11
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    Does this dimmer go bad often ? Is it controlling just lights or is it also hooked to a fan or a heater and how many watts do the lights add up to? – user24125 Sep 11 '14 at 0:22
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Not sure what make and model dimmer you're trying to install, so I'll describe a common installation. Wire colors could vary, depending on manufacturer.

  • Black is the common terminal, and is attached to the ungrounded (hot) conductor feeding the switch.
  • Red is the switched lead (or a traveler in a 3-way installation), and is attached to the switched hot going to the light.
  • Red with white is a traveler, used for 3-way installations. In your situation, you'll just cap this one off.
  • Green is ground, and is attached to the grounding conductor.

Single pole installation
From Lutron Luméa® Installation Guide

If you don't have grounding conductors in your home, you could install a GFCI breaker and you'll be code compliant.

Lutron devices typically have a red and a red/white stripped wire, whereas Leviton has two red wires.

  • This answer might also be helpful. – Tester101 Sep 10 '14 at 23:34
  • even though you qualified by stating "ungrounded (hot)", I would be careful using the term "common" to describe a hot conductor. The neutral conductor is commonly referred to as the "common" conductor in the US. Jeez, was that too many "commons"? – Jimmy Fix-it Sep 11 '14 at 1:32
  • I've never heard the "neutral" referred to as the "common". Can you provide any sources (aside from forums and/or yahoo answers), where the grounded (neutral) conductor is referred to as the "common"? – Tester101 Sep 11 '14 at 2:09
  • I sold residential and commercial electrical supplies for 20+ years in SoCal, many electricians here refer to the neutral conductor as the "common". I s#*t you not. Maybe because they all lead to a "common" bus at the panel? Not sure of origin but absolutely true. I do not "yahoo" for my answers or comments, if I do not know by experience I do not post, when I am wrong I admit, apologize, and learn. – Jimmy Fix-it Sep 11 '14 at 2:22
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    Because a certain area uses the wrong term for something does not make it correct. "Common" used as a term for a neutral is NOT a correct term. Common definitely IS a correct term for one of the connections to a 3-way switch. – Speedy Petey Sep 11 '14 at 2:28

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