Replace a motion sensor with 3-way?


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Old 03-21-20, 06:47 PM
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Replace a motion sensor with 3-way?

I looked around, but could only find the reverse of my issue... I want to replace an existing motion sensor with a 3-way switch. It's at the top of the stairs, while the light is at the bottom, so it doesn't make sense to me.
At the bottom, there are the three wires needed, and a 3-way switch works, but only if the motion sensor side/switch is set to on. I don't see a 3rd wire anywhere in the outlet at the top of the stairs where the motion sensor currently is. So, is there any way to wire a 3-way switch in place of the motion sensor? Or does the lack of the 3rd wire (traveler?) mean there's some high jinks going on at a wall-covered junction. Thanks for any help for this relative noob, and see pics for a tiny bit more detail.
Top of stairs (motion sensor) shown in the top pic, bottom (3-way switch) on the bottom.
 
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Old 03-21-20, 06:51 PM
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You need three wires at the sensor switch to make it work. Looks like you have a conduit system so you should be able to pull in a new wire. Or pull in two wires using one of the existing ones as a puller.
You just need to find the other end. Could be at the fixture.
That second switch looks very odd with three whites on it. Should not be like that with conduit.
 
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Old 03-21-20, 08:13 PM
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That's helpful. I'll consider the "looks very odd with three whites on it." as an upvote for something strange going on behind the walls - I've seen that around here.
In the lower box, there is an accounted-for red wire (the one I'm holding in this new pic). It has no terminations, but seems like one direction leads to the upper switch. I'm not sure where the other end goes - it just heads out the other conduit.
I'll fish around to see if I can find another wire's end, or run one.

 
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Old 03-21-20, 09:22 PM
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You need three wires at the sensor switch to make it work.
No.... you don't. Many occupancy/motion sensors utilize the ground as a neutral.

Based on what I see and intuition.....
- the top conduit with red and white goes to the light.
- the upper/left conduit goes to the current sensor location and the white has been pulled out too far.
....You may be able to push the white wire back into the pipe.
 
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Old 03-21-20, 10:37 PM
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The red wire with your finger on it does not go to the other switch. The other switch has two red coming out of the conduit. Unless the white changes to red on the way that red goes someplace else.
The switch wires might all meet up at the fixture.
 
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Old 03-21-20, 10:43 PM
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Did you read what I posted ?

Look at the left conduit. Red wire connected to power/black splice. Up to switch on red.
Second red wire coming back is switched and goes to the light.

White wire has been pulled out to far.
 
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Old 03-22-20, 09:25 AM
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PJmax, I think that makes sense. I'm looking to see if the white wire is somewhere in the conduit by the motion sensor and if I can fish it out. I'll report back if I make progress.
Thanks
 
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Old 03-22-20, 10:40 AM
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Try pushing it back in first. If you can't push it back in try pulling it out.

Obviously if it pulls out..... it's out. To get it back in turn the circuit off. Either use a snake carefully if you have one or remove one red wire from the switch. Connect a sturdy piece of cord to it. Now pull that red out which will pull the cord into the conduit. Once it's out.... pull it and the white wire back in using the cord.
 
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Old 03-22-20, 11:32 AM
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If you have to pull a new wire in you should pull white and another red or black. With conduit you should not be using the white for a hot. By pulling white and black in you will have a neutral if you ever want a smart switch and the black will be easy to identify as the COMMON connection.
 
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Old 04-25-20, 02:58 PM
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Sorry gents, just getting back to this (something came up...)
I tried pushing the white wire back in as advised, but it seemed to bind along the way. I only then noticed a cover half-way up the stairs which revealed that the white wire goes nowhere.
Junction box pic: Name:  Junction Box - small.jpg
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So, I threaded a new wire (unfortunately, I only had red) between the upper and lower switches. The black-taped wire and the slightly thicker red wire go from brass screw to brass screw on the other switch. The thin red goes from black screw on the upper switch to the light (via the conduit).
Upper switch: Name:  Upper switch - small.jpg
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In the lower box, the whites are joined back together (after getting rid of the third one). The part I'm not completely sure about and checking with you: On the lower switch, I wired the black screw to the black wire (with the short yellow), which is also used by the other switch in the box. Is that correct?
Lower switch:Name:  Lower switch - small.jpg
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Thanks again for your help
 
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Old 04-25-20, 04:09 PM
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You have two red wires and a white wire entering the covered box but you don't have that leaving the lower three way switch.

Likewise.... you have three red wires arriving at the upper three way switch but that doesn't leave the covered box either.
 
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Old 04-25-20, 05:40 PM
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Ah, right. That picture was how I found it, the 'before'. I used the white that didn't go anywhere to pull the new red traveler, then removed the partial white completely.
Below is the 'after' of the junction box. I'm still curious about the connection to the black.
Thanks so much.
Matt
Name:  Junction Box after - small.jpg
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Old 04-25-20, 09:52 PM
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Ahhh..... ok.

In your lower switch picture..... both switches are getting power from a common hot source.
That means that two of the red wires connecting the travelers from that switch to the upper switch are moving the hot between the travelers. The third red wire coming back down from the common on the upper switch is what feeds the light.

Name:  Lower switch - small.jpg
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Old 04-25-20, 10:00 PM
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Cool. So I think you're saying it looks okay (i.e. I re-wired it correctly). It just wasn't completely clear to me if both switches drawing from one hot was typical/acceptable, and that the short yellow I added was an okay way to do things (with the exception of poor color choices). I inferred that it was, though, due to how it was wired when I started this (last picture from 3/21).
Thank you!
 

Last edited by BadAtMath; 04-25-20 at 10:03 PM. Reason: clarity
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Old 04-25-20, 10:20 PM
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Looks ok........... good job. Yellow is ok for a hot color.
 
 

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