My existing conventional light switch was connected only to the red (top, painted over somewhat) and black (bottom) wires shown here. I just bought a Lutron motion-sensing switch and its instructions say it requires grounding.

The new switch has a bare wire and a green wire coming out of it for grounding, but I'm not sure what to do with those. I tried leaving the ground wires dangling in the back and merely connecting the red and black wires from the wall to the switch, as was done with the existing switch, but it did not work.

From what I can understand, the wiring coming from the wall is already grounded because it is attached to the electrical box itself in two places (see photo) using a screw. Do I need to unscrew that and attach the new switch's ground wires to that connection point?

Original wiring Close up of box

  • The new Lutron switch has a bare wire AND a green wire? That's odd. What is the exact Lutron model number so we can look at the installation instructions (Lutron has a great online library of all documentation). – Tyson Jul 16 '17 at 21:37
  • @Tyson Lutron MS-OPS2H. The manual is here: lutron.com/TechnicalDocumentLibrary/0301654.pdf They want me to connect the bare wire and green wire when connecting it to ground. – Stewart Jul 16 '17 at 23:15
  • That's interesting, and unusual. Follow harpers directions and create a pig-tail and attach both the bare and green of the switch to the bare copper attached to the screw at the back of the box. – Tyson Jul 16 '17 at 23:19
  • Is there a reason you're using the MS-OPS2H instead of the MS-OPS6M2N? The latter is a better fit for your install as it doesn't do the naughtiness of putting current on the ground wire, and you have a neutral... – ThreePhaseEel Jul 17 '17 at 3:11

You're required by law to follow the labeling and instructions. This is not optional.

Fortunately, your box contains both real neutral and real ground, so you can provide whatever any smart switch will require. The switched hot is a red wire, which makes it even more straightforward. Unfortunately your drywaller or painter painted all your wires, very sloppy, so you'll need to scrape a bit to identify colors.

You can't put two wires on the same screw. You would need to pull the solitary ground wire off the screw to the left, put a 6-8” pigtail ground wire n that same screw, then splice the pigtail, freed ground and smart switch grounds together.

  • Ok, that makes sense. And I can disregard the white wires that are just capped off? The only ones I need to connect to my new switch are red and black? (and are red and black interchangeable in this case?) – Stewart Jul 16 '17 at 23:29
  • Yeah, you can ignore the white wires if you don't need neutral. You may want it, though. By the way is this motion sensor going to a receptacle? – Harper - Reinstate Monica Jul 17 '17 at 1:55
  • The motion sensor is for a light bulb. Why might I want the neutral? The switch manual is here, by the way lutron.com/TechnicalDocumentLibrary/0301654.pdf – Stewart Jul 17 '17 at 9:18
  • 1
    SE's format is to answer questions not only for you, but for others who also have a similar question. Most quality sensors made to switch LED want neutral. Just tween you and me, I have a feeling the Lutron was built to need neutral, but got a waiver from UL permitting them to bootleg off ground, so they changed white wire to green, hence two grounds. Still, hook it up according to instructions. – Harper - Reinstate Monica Jul 17 '17 at 9:28
  • @Harper -- I'll have to poke at Lutron tech support in the near future and see if they can give us an official word about what the idea is with this configuration. – ThreePhaseEel Jul 17 '17 at 22:38

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.