Why does this switch work?

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Old 11-22-18, 07:59 PM
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Why does this switch work?

Can anyone comment on this working but weird wiring?

Someone installed main floor and upstairs hall lights with BOTH simple switches on the main floor. Im going to rectify that with 3-way switching, but thats another story. But first I need to understand HOW the existing wiring is working.

The top diagram is the main floor hallway. The topmost switch controls the main floor light and is straightforward.

But the switch below it, for the upper floor light (bottom diagram), confounds me. It works: when its ON, the upper the circuit is completed but then the hot and neutral are connected directly through the switch! Id expect at least a blown fuse. What am I missing?
 
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Old 11-22-18, 08:14 PM
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You must be mistaken. If it were wired like shown, the upper fixture wouldn't turn on.
 
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Old 11-22-18, 08:56 PM
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Simply because a white.is wired to a switch does.not.mean it.is.a.neutral.
 
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Old 11-22-18, 09:28 PM
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It would be better if you post some pictures of what you have there.... How-to-insert-pictures
 
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Old 11-23-18, 01:50 AM
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@mossman I understand the sentiment, the apparent impossibility is why I'm mystified. I guess I'm hoping there's something here that I just don't know and that someone out there does.

@pcboss Once I saw the previous owner used e.g. all white 18/2 LVT for the switch legs (nailed to the walls through the middle of the pair of course), I haven't relied on cable color anywhere in the house. My hot/neutral labels are from voltage readings only: hot to either neutral at 115v, 0v between neutrals. Now it IS possible that the (physical black) wire labeled Hot is actually Neutral, but that would mean N1 and N2 are both Hot, and the weirdness at the 2nd switch remains.

@pjmax I actually have a set of photos, but (a) they're so crappy I hesitate to put anyone through follow-the-cables, at least for the moment; and (b) I got frustrated enough that I ripped the switch legs down earlier and decided that tomorrow I'd crawl into the attic and see if I can find an independent pair to drop down to the upstairs light and be done with it. But the legs are still intact, so I could re-attach and take better photos.

Either way, I'll report back tomorrow. Thanks, all.
 

Last edited by rgutter; 11-23-18 at 02:06 AM.
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Old 11-23-18, 06:51 AM
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I'm guessing you have two switch loops and one of the neutrals you have drawn is actually a switch leg. When you are reading voltages, are all the wires connected or do you have anything disconnected? Reason I ask is because you can get a 120V reading on a neutral if it is disconnected and downstream of a light bulb.
 
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Old 11-23-18, 07:12 AM
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The switch connected to N1 is wired like a switch loop, without seeing any more of the circuit.
 
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Old 11-23-18, 07:13 PM
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@mossman @pcboss I think you're both on track here. I realized there had to be something behind the scenes in the wall, but could not figure out what that could be.

The new diagram (with everything outside two dashed boxes not visible) assumes that what was "N1" is actually the closed switch connection to the fixture. This all then makes sense (I think) - except for readings of 120v against the (other) hot input and 0v against the nNeutral.

Thanks again. If there are any further comments I'd very much appreciate them.
 
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Old 11-23-18, 08:18 PM
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Still doesn't look correct. As drawn, the upper fixture would be on constantly.
 
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Old 11-23-18, 08:36 PM
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Definitely not correct. All the red wires are tied together.
If you removed the red tie/splice in the middle of the diagram... it would be correct.
 
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Old 11-23-18, 09:41 PM
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@mossman @pcboss Aaggh! Sorry... I think I've got it right this time.
 
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Old 11-23-18, 10:11 PM
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Your latest drawing makes more sense and it will work correctly.
Each switch controller one light fixture.

How do you plan on putting 3 way switch?
 
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Old 11-24-18, 01:25 AM
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@Iambition I already knew that due to the layout any main floor switch for the upstairs hall was going to involve surface mounting or serious rerouting, so I had decided to go wireless. I already found and tested these RFID units for $15-20.

It turns out to be that rare breed of products that perform way better than expected. (The only drawback is that it seems you can't buy the transmitters separately, so you may end up with extra receivers. But at that price it doesn't bother me.)

Here's the plan incorporating what I learnt today wrt the stuff behind the walls, which remain unchanged. To represent the receivers/relays I made up those ugly double-switch symbols. The switches aren't shown, but they can go anywhere in my two hallways and well beyond. (I think I have the diagram right, but my batting average seems to have been unimpressive the last two days.)
 
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Old 11-24-18, 11:12 AM
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I believe you are using the color black as neutral in your drawings.
Remove the "switch" from the black lines. Neutrals don't get switched.
 
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Old 11-24-18, 05:10 PM
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You're right of course. Quick crappy symbol I made up 'cos I wanted to indicate the physical device which switches the hot line only and couldn't find a ready-made on SmartDraw. Bad choice... Here's a less crappy version.
 
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