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few questions re switch loop (power from light) setup

528 Views 6 Replies 4 Participants Last post by  AllanJ
I'm wanting to install a smart/programmable light switch, to replace the existing switch. I removed the cover to find that it is a switch loop system (the white is hot 100% time and the black hot when the switch is on - there is no neutral). Oddly though inside the box is a 2nd feed of white/black which I also confirmed is another feed of a switched loop setup which I also confirmed is on a different circuit (breaker) than the one currently connected to the switch - this 2nd feed was not connected (was miret'ed). Well kind of - the black from the 2 feeds were tied together (remember, blacks are only hot when the switch is on), but the white (which is hot 100%) is the one that was disconnected on this 2nd feed.

So my question - is it possible that the 1 switch in the past (previous owners) was connected to both sets of switch looped circuits, such that when the one switch was turned it, it would complete the loop of both circuits and basically light-up (power) whatever they were connected to? Or is connected 2 different sweitch loops on different circuits, one one switch not possible (or if possible is it dangerous).

Second question - being the 2nd switch loop was disconnected, I'm curious why and what it powers? I assume there would be no harm in connecting a switch to this 2nd switch loop and seeing what it does when turned on - or does anyone think this may be a bad idea (perhaps it was disconnected for a reason)?

Lastly, the new smart switch I bought needs a neutral, but as mentioned there is not one in my box. However about 3' below the switch box is an outlet which has hot and neutral. If I can fish a wire between the 2 boxes, can I use the neutral from that outlet box? Note that the circuit that the outlet is on is the same as the disconnected switch loop circuit (not the circuit of the switch loop which was currently connected), but as stated the blacks of these 2 switch loops was connected, so they kind of were tied together already (well, it the white was connected, which it wasn't).

I did a little goggling about using neutral from different circuits - in my case I think it would be OK, cause the only reason the smart switch needs it is so it can keep memory power on at all times (in a switch loop system power is only obtaoined when the light/switch is on) - the new switch needs constant power for its memory and programming - so to me it sounds like a little switch like this would not take much power for memory, so using the neutral from below sounds OK to me?

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OK, so I did some more testing. I basically ran a neutral from the outlet below (remember, that neutral is from a different circuit). I then connected the black from the new switch to the 'always hot' wire (which is white in my box), connected the red from the switch to the black in my box (which is the switched hot), the neutral from the switch to the neutral I snaked in, and the ground to ground. As soon as I turned on the breaker I heard sparking so turned it off instantly (it was on a second) - the new switch was smoking from that 1 second. So what did I do wrong. BTW - I put the original switch back in and everything is working normal - hopefully that 1 second didn't cause any permanent problems (though doesn't seem like it).

I'm wondering if maybe I should have switched the black and red wires from the switch - basically put the red to the 'always hot' and the black to the switched hot?? Advice please
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Thanks guys for the info - I learnt a lot, from this forum and much more reading online. Yes, what I did was bad - I removed the neutral and put it back to the normal/original layout. I found a programmable switch on amazon that looks nice but doesn;t need a neutral - definately worth the $40 for the new switch vs trying to rewire the box and lighting it is connected to.

On a side note, the other programmable switch I tried to install (which got the spark and smoke) still smells like smoke (burnt) when I put my nose to it - is it garbage? I have other areas of the house that I could use a timer switch and likely which have normal (non switch loop) wiring, but wondering if the switch is toast now that it got hooked up wrong?

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