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My tenants never turn the lights off in the stairwells of my 3 family house, so I'd like to replace all of the light switches with motion sensors. Here is a crude diagram of how this is set up now.

enter image description here

Each number indicates a 3 way switch. 2 questions:

  1. Can I replace each switch with these sensors?
  2. The #1 switch on the left with the asterisk is in the first floor apartment and I'd like to disable it, so that the first light only comes on from motion in the hallway when a door is opened. How do I take this switch out of the loop?
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Another alternative, that I have seen used in Europe is a glowing timer switch. The lights turn off automatically after a set period of time. –  Chris Cudmore Jul 23 '12 at 12:31
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1 Answer

up vote 5 down vote accepted

You can probably replace the switches with those sensors, but you're going to have to do some creative wiring to work around the fact that they're not 3-way switches, but the switches you're replacing with them are. You'll likely end up with the light being on whenever either of the switches is on. You also might run into trouble if they ran the 3-way switches as a switch loop (no neutral in box), because "smart switches" like these require a neutral so they can use power for themselves to decide when to switch on and off.

Here's what the difference between these wiring schemes looks like if you draw it out:

3-way switches, with neutral and as switch loop

Also note that those occupancy sensors still have a hard-on switch, so your tenants can still just leave the lights on. You might want to look instead at vacancy sensors. (An example vacancy sensor is Cooper Wiring Devices K01-400RW-L, but note that it does not handle CFLs, just incandescents.) These, you tap to turn them on, and they turn themselves off automatically when everyone's gone. That sounds more like what you want.

The how for switch #1 depends again on how they wired your #1 switches and the light they control together. If you diagram out the connections, it becomes straightforward. Until you have enough info to diagram it out, you don't have enough info to rewire it, either.

As an aside, all the exterior stairwell lights I've seen in apartment complexes were on timers. They'd come on around dark and flip off in the morning. I knew they were timers rather than photosensors because a couple times a year they'd end up slightly out of sync with actual daylight hours, but if these are in fact exterior lights, putting them on a photosensor and disabling the switches entirely might be an option.

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Thanks for the information. These are for the interior stairwell of the house. I DO want the lights to come on from either location, since the switches are outside the entry doors to the apartments, so that the lights come on downstairs when entering the house, or when leaving an apartment. Does that change things? –  Vincent Jul 22 '12 at 19:50
    
It means you can safely ignore any advice about exterior stairwell lights. :) Beyond that, not really. Vacancy sensors still seem like a decent option. You'll have to fiddle with whatever you choose to get the right settings on the infrared sensor. You should really draw up a diagram of how the existing lights and switches are wired, including what circuit they're on, since you'll need to power that down before doing any work in the boxes. With that, we could help you more. –  Jeremy W. Sherman Jul 22 '12 at 19:55
    
I would rather the lights come on automatically from any location (entry doors to the house and apartments are right next to the switches) instead of using vacancy sensors. I'm not sure how things are wired - switches were in place when I bought the house. I'll take a closer look at the wiring. Another question is, can I use regular single pole occupancy switches or do I need one of these special "3 way occupancy switches"? –  Vincent Jul 22 '12 at 20:56
    
It looks like those are intended to work along with a 3-way toggle switch, not a pair of occupancy sensors. You can find the installation manual linked from the SmartHome product page. This doesn't seem to be what you want. You should be able to wire up 2 occupancy switches in parallel to the light so that if either one is on, the light is on, and the light is only off if both are off. This should do what you want if both are left in auto on/off mode. –  Jeremy W. Sherman Jul 22 '12 at 21:15
    
Exactly, I want to wire both in parallel so the light turns on from either one. I'll pick up two sensors and start with one switch and see how it goes. Thanks! –  Vincent Jul 22 '12 at 23:08
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