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I was adding an outlet and removed a blank cover over an existing outlet to see what was behind it, and noticed it had a red wire that was capped, and a hot and neutral that were capped together under one nut. I put my multimeter to the hot/neutral combo and it sparked and burned my multi tip. I went and cut the main and uncapped it, and noticed that the end of the neutral was completely gone and burned on the end. There was no melted piece, so my guess is that someone (possibly me) twisted them together and then it melted through the neutral until the wire just evaporated? Interestingly, the inside of the plate had my handwriting on it and said "220v - Marked as Dining Room A/C in breaker. White is ground."

Maybe this used to be the wiring for my old A/C unit before I moved in 15 years ago and replaced my AC? I checked the breaker box and I have a separate breaker also listed as A/C and my AC works just fine with this breaker off. I measured the hot/neutral and it measures as 115v, not 220. The breaker is 30 amp. I restripped the wires to remove the burnt ends and then capped them individually and put them back in the receptacle. Everything seems to still be running fine in my house and my A/C works. I then cut the breaker to it so they aren't live.

I have not touched this outlet in at least ten years. I guess my question is, is that a danger to have the hot and neutral capped together and if so, why didn't it trip the breaker, which has apparently been on this entire time? And lastly, I assume it's fine now that I capped them all individually and cut the breaker?

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  • To answer your question, no you cannot connect hot and neutral together ever. Sometimes the white wire is not used as a neutral, but used as a hot on a 240v circuit or a switch hot wire from a switch.
    – crip659
    Aug 7 at 23:27
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I tend to disagree with the previous answers. If you had a label saying "white is ground" and found it vaporized in the vicinity of a hot wire, then somebody connected the wrong wires and melted them on the first application of power. Very likely the circuit breaker DID trip, but the wire was already melted. Had you been near the junction when it happened, you would have heard a "pop" from the wire blowing out. After resetting the breaker, the wire was damaged to the point where it was no longer tripping the breaker.

Sticking your tester probe in the nut may have created a new short with the remains of the white wire.

Yes, it is safe with the wire ends protected and the breaker off.

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Others will go into more detail but it is an interesting setup. Red is a second hot, used in 3 way switches. White can be a hot but convention is to mark it with black sharpie/electrical tape to denote it is a runner.

Wire nutting the Black/White would seem to indicate this used to be a switched circuit that used white as a runner, somewhere... but... you'd really need to trace everything to figure out what's happening.

As an aside I'll share this link. My first guess was a 4 way switch or fan but the age is a bit iffy. https://www.electrical101.com/optional-4way-switch-wiring-using-nm-cable.html Be careful.

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Wow, this is a new one!What might have happened is the wirenutted hot and neutral (whoever did it) made a lousy connection and the wire fried before the breaker could trip, breaking the errant connection. When you inserted your multimeter probes, you jostled those wires causing them to make contact again. Again, this is speculation, but I've seen sparks fly and breakers not trip. (apologies to "No Sparks Please"!)

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