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We have checked all the outlets and light switches and they all work. The power went out in three rooms and breaker did not trip. We took pictures of the breaker wires and noticed this one wire looked discolored. Do you think this maybe the reason the power is out? Does the wire look burned?

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chelly
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    That one wire did get hot enough to start melting the insulation. That should not happen, and it's interesting that the wire with the problem also looks like it was clamped down on in more than one spot as if to fix a bad connection. Did you attempt to re-clamp that wire or was it like that already? – JPhi1618 Jun 03 '19 at 14:49
  • That wire was like that already. Since the power went off we have keep the breaker off. When it is on it does give us a reading of voltage. That is why we keep it off. Before the power went out the lights were flickering. So I think there was to much going on. Do you know if each neutral wire belongs to each breaker switch? – chelly Jun 03 '19 at 14:59
  • Each single hot wire (black) should be paired with a single neutral wire. There are some incorrect wiring techniques that can lead to two hot wires sharing a neutral, and then the neutral can be dangerously overloaded. This can happen due to inexperience or even accidentally (mixed with inexperience). – JPhi1618 Jun 03 '19 at 15:05
  • So being that the wire did get hot. Does that means we need to replace the whole neutral wire from one end to the other? – chelly Jun 03 '19 at 15:08
  • I'll let someone with more experience answer that, but the reason you lost power is probably because another connection along the line has melted. Outlets and switches are not as "strong" as that connection in the breaker panel and would fail first due to excess heat. A breaker should trip before it gets that hot, so that's an issue that may take an experience electrician to troubleshoot in person and figure out. – JPhi1618 Jun 03 '19 at 15:10
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    @jphil you are wrong , a code recognized method of running 2 hots on 1 neutral is totally code compliant and is called a mwbc multi wire branch circuit. Covered in NEC 210.4. A loose connection can cause serious overheating and burn the hot or neutral completely off without causing an overload. – Ed Beal Jun 03 '19 at 15:21
  • When you say a loose connection. Do you mean on one of the outlets or switches? Do you mean on the Breaker Box? – chelly Jun 03 '19 at 15:25
  • @JPhi1618 MWBCs are fine if wired correctly. It may be that OP's is not. We can fix that. – Harper - Reinstate Monica Jun 03 '19 at 15:39
  • Please follow that neutral to the point where it enters the panel or diverges from the hot wire(s) - be prepared for 2 hots. This will be at a cable end, cable clamp, or conduit entrance. Describe it or shoot a pic. Then... follow each hot to its breaker and describe those or shoot pics. I am mainly interested in ampacity and whether it is a single, a 2-pole, or a double-stuff (note those last two are different things). I'm also curious about panel type since this works differently on some. – Harper - Reinstate Monica Jun 03 '19 at 15:41
  • @EdBeal, Right, I was referring to incorrectly done MWBC, which are a common source of overloaded neutrals. – JPhi1618 Jun 03 '19 at 15:41
  • I did cover that in my answer but your comment was not clear, Harper provided the same advice as I did, follow that white back to the cable that enters the box. – Ed Beal Jun 03 '19 at 15:47
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    OP did you loosen that screw? Compared to the others, it's loose as a goose. That would explain heat from arcing. – Harper - Reinstate Monica Jun 03 '19 at 16:23

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To me it looks like the wire may have been loose in the past and retorqued notice the gouge in the wire a torque driver was not used to do that much damage to the wire. Since you are having flickering or lights / circuits out and you have checked the panel it is time to find the problem. If you have other outlets or lights on that circuit that are working the problem will be at the last working outlet or device or the first non working one.

The most common cause is a back stab connection being used, these are when 14 awg wire is used and just pushed in to make the connection ( not under a screw or clamp), the next place is broken wires at a connection or 1 wire pulling out of a wire nut. I listed them in the order I find them in over the years. The big problems with back stabs is they may look fine on the outside but with a failed connection there is usually some deformation of the plastic and or insulation but you may have to look close. When you find the problem if the insulation is intact cut the arc marked wire back to good copper, this is enough as only the loose connection area was heated not the entire wire.

There is a small chance the problem could be a bad breaker, or panel and an even smaller chance it is a very old MWBC that did not have handle ties and the 2 breakers got separated and put on the same leg. To see if it is a MWBC trace that white wire back to the cable coming into the box. If there is only a black you are done. If there is a black and red (the most common hot colors) trace the black and red back to their breakers. They should be next to each other and by today’s code have handle ties, or a single handle, many years ago they just had to be in adjacent slots. If this is true the panel wiring is correct. If the breakers are separated someone messed up and they need to be together a handle tie or double pole breaker is the safe way to go.

Go back and find the source of the problem it usually is the last working outlet or device or the first non working outlet or device. And it could be the white or hot wire at those locations.

Ed Beal
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  • The gouge in the wire looks deep enough to me that it may have occurred as a result of melting at an earlier time. It would take a ridiculous amount of torque to cut that far through the wire, right? (Not saying some folks aren't that careless, but that's really deep.) – isherwood Jun 03 '19 at 15:50
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    I have seen it many times even by journeymen, that’s why torque drivers are required now. – Ed Beal Jun 03 '19 at 15:51
  • So, you're suggesting the melted insulation on the wire in the panel was because of the previous, possibly loose connection? – JPhi1618 Jun 03 '19 at 16:03
  • I have seen melted insulation and burned off wires mor often than a split mwbc but I have found those in years past, I would say in the last 15 years I have found bad breakers more often than the couple of split up single breakers and tandem powering a mwbc. For those that don’t know a tandem or double stuff breaker is one that has 2 breakers on the same pole, mwbc circuits must be on opposite poles. – Ed Beal Jun 03 '19 at 16:08
  • @EdBeal In a factory I recently found a MWBC with 3 hots sharing a neutral. No, it wasn't 208/wye. Based on panel markings they were on L1, L1 and L2 respectively, but upside they were evenly loaded and used at the same time, so that probably saved them. – Harper - Reinstate Monica Jun 03 '19 at 16:28
  • Wow I have never seen a miswired 3 phase mwbc, they were marked but did you measure them? I use them all the time. But maybe a dozen or a few more in residential but less than 2 dozen and most of those were split up and a few tandems. But with larger services I rarely see them or haven’t for a few years in residential work. – Ed Beal Jun 03 '19 at 16:45
  • I want to start out by saying Thank you everyone. It turned out to be the first ceiling fan we installed that the neutral wire disconnected from it. My husband took it down and check the connections and it was not connected. Once he connected the wires he turned the breaker back on and the power was back on. Yay! I think that because it was not connected properly caused the power to go out. – chelly Jun 03 '19 at 17:24