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[Edited from original version apparently read into a cell phone's voice reco.]

I am trying to wire a dimmer switch into an existing light switch that was in the box before. It had three wires connected to it:

  • a white wire which was labeled line negative on the old switch [NEUTRAL]
  • a black wire that was labeled line positive on the old switch [ALWAYS HOT]
  • in a red wire that is presumably the power wire To the light the light. [SWITCHED HOT]

The dimmer switch has a ground wire, a red wire, a black wire, and a striped red wire. According to the instructions on the dimmer the black wire should be connected to power; the red wire should go out to the light; the striped red wire should just be capped; and the ground should go to the ground.

What confuses me in the situation is that the white wire coming out of the wall doesn’t actually attach to anything. Is this correct? Do modern dimmers not need a negative [NEUTRAL] return?

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  • I edited your question to fix formatting (!) and install the proper names for the wires in brackets (e.g. [NEUTRAL]). This will make it simpler to discuss them. (Note that this being AC power, there is no such thing as positive and negative, but the concept of one conductor being near safety earth is at least correct.) – Harper Sep 15 '18 at 21:13
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The white is a neutral or grounded conductor, required for the old receptacle that was there.

In general, switches (including dimmers) just "make or break" the hot conductor; no neutral needed. If you no longer intend to use a receptacle in that box just nut and tape it and tuck it carefully into the back of the box.

  • As a note, some modern dimmers and switches that incorporate stuff like timers, lighted displays, electronic features, RF transmitters, etc., do need a neutral conductor. Yours does not. – Jimmy Fix-it Sep 15 '18 at 19:04
  • Wired the way you described, worked like charm – user379468 Sep 15 '18 at 21:16
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You need neutral in that box. Now.

I don't mean for your current dimmer. I mean as of 2008?, they changed the Electrical Code to require that you pull neutral down to almost every place a switch can go. This being a "switch loop" circuit, it must be wired -- by amazing coincidence -- exactly the way it is now. Lucky you.

That means you must keep it that way.

Your particular dimmer does not require neutral. Increasingly, more and more of them do. That's because dimmers, motion sensors, lighted switches and smart switches are capable of doing more cool stuff when they have real neutral. Eventually I assume you'll upgrade to LEDs and experience the limitations of this dimmer, and want to change to a better one.

In the meantime, just put a cap on it (orange or blue wire nuts are about right) and tape the cap down to the wire pretty aggressively, because wire-nuts fall off single wires very easily. Neutral loose in that box would be a problem.

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