I went to replace an 90s era fluorescent electrical fixture, and when I took the old one down I had a black hot connected to the fixture’s black, and two neutrals twisted together along with the fixture’s neutral. Nothing strange so far. Everything was working normally. FWIW, it’s an old house and so this is early Romex with no ground- what I call snakeskin Romex.
I would never have noticed what comes next, but as is typical of this house someone decided wire nuts are just too expensive and had made the pigtails with electrical tape. I briefly thought “It’s been fine this long” but then decided I should spend the 20 minutes of frustration and remove the old tape and do it right with Wagos or nuts (I’m in love with Wagos). It was then that I realized I have the following; Had I just used the existing pigtails I would not have known (Pic to follow)
The black hot is switched. Good.
One neutral is always cold. Good.
One neutral is always hot unless I kill the breaker.
If I disconnect the two “neutrals” the two lights downstream don’t work. If I connect a load it operates as expected, via the light switch. If I connect the two neutrals with no load between them and the hot everything downstream works.
So I could put it back together as it was, and life goes on, and it hasn’t caused a problem in decades. But if I can figure this out without ripping open the walls, that might be nice. Any thoughts? Beyond “call an electrician?”
Oh, and there is another electrical tape “wire nut” inside the box, but I haven’t pulled it out to see what’s connected to what in there. I was going to do so, but decided to post this while I ruminate on it.
You have a shared neutral*. Put it back together the way you found it and it should work fine.
What’s happening here is that power comes from your panel, to a different light (or something else), then the neutral from that place comes over to the light you’re working on. As long as all the neutrals are connected, it’s fine, since it has somewhere to go (back to the box/ground) but as soon as you pulled them apart, you broke the circuit and that neutral is now live.
So this is sorta what you have going on:
You’re working on the light on the right. You have a hot (black) and and some neutrals (blue).
One neutral goes to the breaker box, one comes from the other light, the third is the one coming from the (removed) fixture. Those are what would’ve wire nutted (or electrical taped) together.
When you broke apart the wires in the blue circle, the power flowing through the light on the left has nowhere to go and leaves the neutral hot.
If you know which light it is, turn it off or remove the bulb and it won’t be hot anymore.
Thanks, makes perfect sense. And once you said it was a shared neutral (something I didn’t think was legal, but the house is 80 years old) it made perfect sense. Glad to know this doesn’t have to turn into rip the whole place apart.
ETA: And that explains why when I put my meter across them before hand I didn’t see any voltage. I thought I must have just not got a good contact between the probe and the wire and got a bad reading.
In an 80 year old house, it’s still (should be, I think) legal. In a newer house, built to current NEC standards, it’s still legal, but the two breakers that share the neutral have to be tied together so if you shut off one, the other one shuts off as well.
(NEC 210.4(b))
Also, you have to be careful with these. Provided the hots are on separate phases, which they should be for a shared neutral situation, if you end up with the two neutrals connected to each other, but not connected to the box, you’ll have 240v flowing through the devices. It would be like a 240v appliance, like an electric water heater. Two hots, no neutral.
And there’s other problems that can arise if they’re on the same phase. But, wired properly, it’s perfectly safe.
In any case, if it’s been that way for 80 years, rewire it like it was when you found it and you should be fine.
And, of course, if you’re unsure of anything, call an electrician.
