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I wanted to install motion sensor switch in my bathroom. Its a small closet like room with a toliet sitting area. Most US users know what I am talking about. In it are two switches. One switch controls a 14W LED light and the other exhaust fan.

This is what it looks like. Imagine two dumb regular switches here.

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Now what I wanted to do was install one motion sensor switch that will control both the fan and light. So I bought a leviton motion sensor switch: https://www.homedepot.com/p/Leviton-2-Amp-Single-Pole-Decora-Motion-Sensor-In-Wall-Switch-Auto-On-in-Light-Almond-DOS02-1LT/317168137

I opened up both the switches and connected the wiring of each i.e. black & black of each to the black of motion sensor and neutral and ground of motion sensor to the ground of wall switches. Now when I turn on the power. Everything is on. LED is running + Fan is running. But when I click on the on/off switch of motion sensor to turn them off, nothing happen. They keep running.

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I thought ok, there is either something with the motion sensor I just bought or something wrong with the wiring. I connected only the LED bulb to the motion sensor and it worked perfectly. It turns on/off when I click the motion sensor switch. Why doesnt they turn off when both the switches are connected? Is there something basic I am missing here?

I went and bought a Lutron 2amp motion sensor switch and that too behaves in the exact same way. Works when alone, keeps running when both switches are connected.

NOTE: I have done similar setup in two other bathrooms of mine (LED+Fan on one motion sensor switch) the exact same wiring setup (black on black and ground+nertual to ground only) and they are working fine there. Its only here the swtich is acting up. I also tried connecting neutral of motion sensor to white (you can kinda see in the back) and still this one remain stubbornly on all the time.

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3 Answers 3

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So many wires, so little time...

Instructions below, except as noted, apply generically to any similar motion sensor, dimmer, timer, smart switch, etc. For this specific switch, instructions should be included in the box and are available online.

Neutral/Ground

Generally speaking, but check the instructions to be sure, if you actually have an available neutral for the correct circuit in the same box then you are supposed to use that. The "green sleeve over neutral to switch and connect to ground" is only if neutral is not available. But while that is marginally important for safety (marginally, because if you were not allowed to do it then it would be a "neutral required" switch and the green sleeve would not be included), it should not affect operations. But you should correct that.

Identify Wires

This is the key. Starting with your best recollection of the original configuration, you need to identify every single wire in the box. Some will be easier than others.

  • Figure out how many circuits you are dealing with. Most likely one, but that is key. If one breaker turns off everything (Non-Contact Voltage Tester doesn't register on anything with a single breaker off) then proceed. If it takes two breakers, except for a handle-tied or double breaker that is an MWBC (two hots, one neutral) then STOP.
  • Multiple white wires in a wire nut - almost always neutral.
  • Bare wires - ground - all together, connect to any/all switch grounds.
  • Hot/line - this can be black or red or possible white (in an old-style switch loop). If all wires (except grounds and bundled whites) are (carefully, so you know how to reconnect) separated and you turn power back on, you should have exactly one hot wire.
  • Switched hot - you should have one switched hot for the light, one for the fan. If you think you have found each one, connect it (just the one wire, not both at the same time) to the hot wire and turn power back on to verify. Mark the one for the light with red tape, the one for the fan with blue or yellow tape.
  • Ongoing hot/load - you may have one or more of these wires feeding other devices. You can identify by connecting, one at a time, any spare non-white wires to the hot wire and seeing what things in the rest of the house start working again.

Once you have identified all the wires:

  • Switch ground to all other grounds.
  • Switch neutral to the neutral bundle. (I think I see one in the box, if not then yes connect to the grounds and put on the green sleeve.)
  • Switch hot to the incoming hot and to any/all ongoing hot/load wires.
  • Light and fan switched hots to switch switched hot.

An ordinary ("dumb") switch will simply have two connections for hot and switched hot and you can designate them as you choose. A smart (motion, etc.) switch may designate those or may not. If it does, follow the hot/line and switched hot/load designations. If it doesn't then pick one for each, and mark the "switched hot" with red tape. This switch specifically says:

NOTE: This device is designed so the line and load wires can be wired interchangeably.

Fan?

The specifications (on the Home Depot page and in the manual) reference various types of lighting as well as a pure resistive load. There is no mention of fan or motor loads. There are other motion sensors, including Leviton Maestro, available at Home Depot that specifically include fan usage. My hunch is that any reasonably flexible lighting switch (as long as it is not a dimmer) will work fine with a fan, but there may be issues.

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    So many wires, so little time ... lol. nice detailed answer. yes, its one circuit breaker for both the switches. you are right about hot wire. I randomly picked two blacks and connected them together with black of motion sensor. I assumed two hanging out on the top are the same but I guess they are not. I think that is my problem. Commented Feb 12, 2023 at 15:07
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You appear (to the extent I can decipher that paint-splattered mess) to have neutral in the box, and the joining of ground and neutral is definitely wrong.

Most likely you connected the always-hot of one of the original switches to the switched-hot of the smart switch. Screw positions mean nothing regarding which connection is always-hot, particularly on a dumb switch.

You only need one always-hot supply to the smart switch, and if the fan and light were not on the same circuit to begin with, you cannot join the two circuits at this switch, (or anywhere else.)

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  • sorry I dont understand what you are saying. I did a similar setup in two other bathrooms of mine (LED+Fan on same motion sensor) and they both are working correctly. Its only in this bathroom here they are not. I updated my question. I have also tried connecting netural of the motion sensor to the neutral white wire in the back and it still has no effect Commented Feb 12, 2023 at 14:53
  • When you connect unswitched hot to switched hot, the switch won't work. From your symptoms, you have done that here. Commented Feb 12, 2023 at 14:56
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Let's break this down into simple steps:

With the electric to the box off, observe just the black wires. One goes to the fan. One goes to the light. Find those 2 wires that exit the box without being connected to anything else. Those are your "load" wires. Bend them to the side, you you don't get them mixed up.

Look at the remaining 2 black wires. They should be connected to another black wire with a wire nut inside the box. Those are your hot or "line" wires. If they are NOT connected with a wire nut. If you have 4 separate black wires out of the box, you have 2 separate circuits and cannot connect the 2 together. This is what Ecnerwal is trying to tell you. STOP THERE. you cannot connect both light and fan on one switch.

If the case is that the 2 black wires are connected to a third with a wire nut, you remove the 2 wires. The remaining wire is your hot or "line" wire. That black wire gets connected to the pigtail on the new switch marked "Hot" or "Line" Your 2 black wires to the fan and light get connected to the new switch remaining black wire marked "Load" or "Out"

The green wire with the yellow stripe is connected to the 2 ground wires from the box. The white wire with the green sleave from the new switch is capped with a wire nut and not used.

This will make the switch work.

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  • The white wire with the green sleave from the new switch is capped with a wire nut I don't think so. If this was a "don't really need it" wire, they wouldn't supply the green sleeve. I believe that is a required wire for proper switch functioning, the only question is whether it connects to neutral (which it should if available) or ground. Commented Feb 12, 2023 at 15:25
  • From the manufacturer: " Can be installed with or without neutral wire." Commented Feb 12, 2023 at 15:29
  • Correct. But I'm 99% sure (haven't read these instructions, but have read many in the past, is that "without neutral wire" (in a "with or without") does not mean "don't connect the so-called-neutral from the switch to anything", but rather "if you don't have a true neutral available, you can connect the so-called-neutral to ground instead and then you mark it green with the provided sleeve." In fact, I'd bet that in addition to it not working with the white (green optional) wire connected that if you do a continuity check on the switch (not connected to anything) you will find that the Commented Feb 12, 2023 at 15:35
  • green ground wire is connected to metal yoke of the switch and neutral white (green sleeve if needed) wire is not connected to the metal yoke - i.e., it only becomes "ground" when needed. Commented Feb 12, 2023 at 15:36

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