I'm trying to replace one of the 3-way switches in a 4-way switch circuit with a 3-way occupancy sensor.

Here's my current wiring for the occupancy sensor:enter image description here

And here's the current wiring for the other 3-way switch enter image description here

I haven't touched the 4-way switch.

Before I changed any wiring, the black screw on both 3-way switches was connected to the black wire.

Here is the current behavior of the circuit:

When occupancy sensor is OFF:

  • 4-way switch does not function
  • If the 4-way switch is in the OFF position:
    • 3-way switch does nothing
  • If the 4-way switch is in the ON position:
    • 3-way switch works, but only if I switch it slowly. If I switch rapidly, it only works every other time the switch changes.

When occupancy sensor is ON:

  • 3-way switch works properly
  • When the 4-way switch is switched, the lights flicker off while the switch is in between positions.

Any thoughts on what I've screwed up with my wiring?

  • What make and model is the occupancy sensor? – ThreePhaseEel Dec 27 '16 at 2:23
  • Some of the occupancy sensors require the neutral. The 2nd switch only has 2 wires going to it is it a digital model that doesn't require the travelers? If this is the case you will need the same brand and model for the system to communicate to the other switches. – Ed Beal Dec 27 '16 at 2:34
  • @ThreePhaseEel it's a Lutron MS-OPS5MH-LA – Jonah H. Dec 27 '16 at 3:29
  • @EdBeal there are three wires in the second switch, I just have the one of the travellers and the hot wired together with the yellow wire, as instructed by the occupancy switch's installation directions. – Jonah H. Dec 27 '16 at 3:32
  • Can we have photos of the inside of the occupancy sensor box and the four-way box? – ThreePhaseEel Dec 27 '16 at 12:41

You generally have 3 conductors in a 3/4-way switch loop, and you can't misuse ground as a conductor. That leaves Only two ways to do it (short of a relay and low-voltage wiring):

Smart switches in the auxiliary locations

Obtain smart switches designed to be "remotes" for the main motion sensor and interact with it electronically, either using 1 wire as a data line, or wireless via power-line signaling or radio.

Very lucky topology

This can only work, if

  • supply power comes in to the light, the switches are all one spur, and the motion sensor is in the first box.
  • supply power comes into the same switch box as the spur to the light, and the sensor is in that box.
  • the essential interconnections are in conduit, and you can pull more wires.

Otherwise you'll have a spot where you need 4 wires, and you only have 3 in the walls.

Your sensor needs three wires coming in: always-hot, switched-hot from the switch, and neutral for the light's current return. The sensor doesn't need neutral, but the light does, so inevitably neutral must come back this way.


It does not support a 3-way switch. It supports a plain switch which switches between 'open' and always-hot or switched-hot. If it is placed in one position and the one other position was a 3-way switch, then they have you rewire the 3-way to be a plain switch.

Since you have two remaining positions with manual switches, those two positions must together emulate the behavior of a plain 1-way switch. They way you do that is the classical 3-way circuit. The 4-way switch needs to be swapped out for a 3-way. Which you happen to have spare. However, if supply to the light also travels the switch wires, you'll need 4 wires in that segment:

  • always-hot for the smart switch
  • messenger 1
  • messenger 2
  • neutral to return current from the light

This is one more than a traditional n-way, installed with the usual 14/3, and you can't retrofit a consuctor.

This does work if your topology is just right: the two remaining physical switches are on a spur. In that case you won't need to carry lighting power (i.e. The neutral) between switches and you'll have enough wires.

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  • I found this question which has an answer that seems to indicate via this document that this is in fact possible if I were to purchase two of these companion switches. Is that correct? – Jonah H. Dec 27 '16 at 7:40
  • Ha! I fell to the narrow thinking I am usually warning others about! Yes, if you go smart switxhes in all locations, you are sympatico. Then instead of 2 messengers you have just 1 comms wire (or 0 if it uses signal-over-power or wireless). – Harper - Reinstate Monica Dec 27 '16 at 14:52

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