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I'm trying to install a Lutron Maestro sensor dimmer to replace an existing bathroom light switch (on the left in picture) that is beside a fan switch (on the right in picture), however I can't seem to make sense of the wiring because:

1) the upper terminal of the light switch has two wires leading to it (from what I've read it might be the Jumper taking power to the fan switch?)

2) the existing switch doesn't appear to be grounded as there is no wire attached to the green screw on either of the switches. I also can't seem to find a screw in the metal box that would be used to ground the switch.

I've attached a picture of the existing setup and the new sensor dimmer I'm trying to install.

Many thanks in advance!! existing wiring set up

Lutron Maestro sensor dimmer

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    Welcome to DIYSE. You might take the tour to learn about how this site operates. – isherwood Mar 27 at 15:16
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    Does the switch on the left in your first picture control two things? – JPhi1618 Mar 27 at 15:29
  • I did not mention in my answer but having 2 wires under a screw (not a clamp) is a code violation. Under a screw the wire should be wrapped 2/3- to 3/4 around the shaft so the loop tightens when the screw is turned. These connections should be pigtailed and a single wire to the screw. – Ed Beal Mar 27 at 18:43
  • The switch on the left only controls the lights. I appreciate all the help!! Thanks for the info on the 2 wires.. I'll pigtail them. – Chris Mar 27 at 20:06
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I can’t tell but I think I see a bare copper middle right or possibly a green screw , this is the proper grounding point. It looks to me that each switch has a black wire that goes to the same wire nut this would usually be the hot because if the hot was on the top of the left switch when you turn that off the other switch would not work. My guess is the fan has a separate conductor run for the light , prior to remote controls it was common to run 2 circuits to a fan 1 for the fan 1 for the lights so either or both could be on or off.

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    Adding on something I noticed, it looks like a metal box. If so, (this for the CO, Ed knows this) it is probably the ground. The incoming ground while it attached to the metal box and the old switches are grounded just be being in contact with the metal box. – Ack Mar 27 at 18:18
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1) the upper terminal of the light switch has two wires leading to it (from what I've read it might be the Jumper taking power to the fan switch?)

Correct. Switches connect always-hot to switched-hot (or not). Most of the time when there's more than one switch in a box, the always-hot must be split to reach multiple switches. The installer usually does that in the most expedient way possible since the installer has a lot of stuff to install that day, and some of those methods look weird.

2) the existing switch doesn't appear to be grounded as there is no wire attached to the green screw on either of the switches. I also can't seem to find a screw in the metal box that would be used to ground the switch.

Note the screws you removed to pull the switches out of the junction box. Note how those screws go through a metal yoke (that's what that's called). Note the junction box is metal. That is the grounding path: through the screw threads.

"Through the threads" is not allowed for receptacles, but it is for switches.

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  • Thanks for the help! So, 1) would it be okay to simply wire the sensor dimmer switch the exact same way as the old switch was wired (i.e. with the hot and jumper wire connected at the upper terminal)? And 2) forget about the green ground wire on the new sensor-dimmer switch since it is being grounded by the screws at the yoke? – Chris Mar 29 at 14:20

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