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I have the Lutron Maestro 2 Sensor Switch. As seen in the picture, it has a ground and 2 black wires.

My junction box has black and white, and is a metal junction fully grounded. Im not sure what I do with the second black wire on the switch.

enter image description here

Update:

@manassehkatz pointed out that the wiring was most likely a switch loop, where the installer just used the black/white for the hot and the switch-hot, therefore confusing my insanely newb brain when an unmarked white was being used for the return hot from the light.

THANK YOU

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    For an explanation of why the box just has a black and white wire in it, look up "switch loop". Here is one question about it, but there are many. – JPhi1618 Apr 3 at 14:51
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    Those wires in your wall are not color-coded at all. They are black and white because those are the standard colors used in all cables. – Harper Apr 3 at 17:53
  • Can you post a photo of the inside of the box please? – ThreePhaseEel Apr 3 at 22:58
  • will do this weekend! thanks @ThreePhaseEel – cgmckeever Apr 3 at 23:31
  • See the solution below. Turns out just an insanely poor wire choice for a switch loop that confused me hard. But walking through it helped me understand it a whole lot better. Did go in there this weekend and verify/clean it up some now that I know a little more what was going on in the rats nest – cgmckeever Apr 8 at 14:58
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Unfortunately, the Installation Guide doesn't say much. It shows the two black wires but does not have any indication as far as which one goes to hot vs. switched-hot. The implication is "it doesn't matter".

However, the marketing information (and the installation by omission) makes it clear that no neutral is required. But the switch has to get power from somewhere to run the motion sensor. The instructions indicate this is by using ground:

  • Both bare and green ground wires are required to connect to ground. If no ground is available, consult an electrician. Device will not function if it is not grounded.

So that tells me two things:

  • The green ground is NOT for safety but rather in place of neutral for the motion sensor power. According to Q&A on homedepot.com, the switch uses < 1 watt when "off". That puts in the relatively safe range as far as current running over the ground wire. While using ground in place of neutral is not normally permitted, it is still allowed within certain limitations, and it avoids the problem of either (a) requiring a neutral in the switch box which many boxes simply don't have or (b) running a small amount of current through the switched line when off, which works fine on incandescent bulbs but on LEDs will often result in either flashing lights or a very low constant glow. It might put it below the normal threshold of a GFCI, but I wouldn't count on it.

  • The bare ground is for safety.

Provided your box really is properly grounded, connect both grounds (green & bare) to the box, connect hot to one black, switched hot to the other black, and you're done.

This actually makes for a very simple and almost foolproof installation. But they could have made it totally foolproof by being upfront in the instructions about how it uses the wires. A classic example of dumbing down instructions too far, raising more questions instead of making things easier.

Beware of GFCI

As I understand it (pros can chime in, of course), lighting circuits in areas that require GFCI for receptacles (bathroom, kitchen, laundry room, etc.) do NOT need to be on GFCI. They can be on GFCI, and if so then a switch like this might be detected as a ground fault. If that happens then you should either move the lighting to a different circuit or (generally much simpler) pigtail the lighting to the LINE side of the receptacle instead of daisy-chaining off the LOAD side.

  • Comments are not for extended discussion; this conversation has been moved to chat. – Michael Karas Apr 4 at 12:59
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    You sir, are a party pooper. There was a lot of good info in there that helped solve the issue. I have tried to summarize. – cgmckeever Apr 8 at 14:57
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Assuming you're replacing an existing switch, then

  • the black wire in the gang/junction box (hot) will go to one black wire on the sensor switch.
  • the white wire in your gang/junction box is likely the switch wire, which will go to the other black wire on the sensor switch.

It is also important that the switch is properly grounded to function.

  • Ground via the green wire from the switch attached to grounding screw on junction box. Appreciate the response, it perplexes me that the white (from the box) goes to the black (switch). Is white the neutral? – cgmckeever Apr 3 at 14:15
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    Neutrals are always white, but the switch wire can be anything, even white... That's why I'm assuming you're replacing an existing switch. Switches won't use a neutral (except for special cases, e.g. Smart Switches). Some houses won't even have neutrals exposed in the boxes when they're reserved for switches. If you could take a picture of your box, then it may be easier to tell. If the previous switch was connected to the black and white wires, then the new switch will be connected similarly. FWIW, I installed this exact switch in my garage just last Saturday. – Sam Apr 3 at 14:20
  • Can get a picture later, but yes/sorry -- it is replacing an existing standard toggle switch, and yes, it was connected top/black, lower/white – cgmckeever Apr 3 at 14:52
  • Yeah, then just connect both of those to the two black switch wires; the order does not matter, and no photo is necessary. – Sam Apr 3 at 15:00

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