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How do I install a Lutron occupancy sensing switch on a switch box with two wires?

Also, what do I do with the green ground wire?

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    Can you give us more info? What are you calling a "two wiring system"?? Do you mean there are only two wires at the switch? And what part # switch are you using. They are not all the same. Jan 7, 2016 at 21:49

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If you mean there are only two wires at the switch then you cannot use a typical occupancy sensor at this location.

This type of switching is called a switch loop. The hot is brought down on the white and the switched black goes up to turn on the light. There is NO neutral wire in a two-wire switch loop.

This is why new codes require a neutral wire at a switch box location, even with a switch loop.

The ground should be connected to the ground wires in the box. If none exist, or the box is metallic and grounded, then just fold the ground wire into the box behind the switch. You should definitely check the instructions to see if the ground is absolutely required. Switches in existing applications that are non-grounding can be replaced with new, but some electronic switches require a valid grounding conductor.

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  • I remember installing a handful of these in a mezzanine of an old office. They do exist but they are often mail order and $50-60 ea Jan 8, 2016 at 12:56
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How do you do it? Well, without compatible wiring, you don't. Here are your options:

  1. Get another sensor meant to be installed in a switch loop without neutral. (Good luck)

  2. Run a new 3 conductor+ground cable from the light to the switch and use it to supply a neutral to the switch on white and carry its switched hot leg back to the light on red.

  3. Run a new 2 conductor plus ground cable from the breaker panel or another junction box to the switch, and then another 2 conductor plus ground from there to the light.

  4. Use some sort of home automation hardware with one control module tucked away in the light's jbox and a sensing module in the wall where the switch was.

You can make it work without having grounding in the switch' junction box. But if you are running new wire, you should properly ground things as much as possible.

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    If the existing wiring is #12 on a 20A breakeryou must stay with #12. The suggesting to use #14 assumes the existing circuit is #14. Jan 7, 2016 at 22:21
  • True. And most lighting is 15A on #14. And the asker didn't say anything about 20A.... And "must" is a relative term. The light is not going to need 20 amps of ampacity. Only the NEC would "need" it, and as far as I'm concerned, adding a grounding conductor and a neutral are much more relevant and useful. Jan 7, 2016 at 22:33
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    No, "must" is a definite term. If the breaker is 20A for a lighting circuit you MUST stay with #12 (minimum). The OP said nothing about #14 and 15A either. ........... I was just clarifying for the OP or anyone else reading. Jan 7, 2016 at 23:15
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    I don't know why you are getting all bent out of shape over this. I merely made a simple clarification. I could have edited your post but I don't like doing that to another professional. You are, aren't you? Jan 7, 2016 at 23:36
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    Not to get technical, but I didn't make an assumption. Jan 7, 2016 at 23:41

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