I have a friend who has a 200amp panel in an early 90s' house and he keeps having neutrals burn up at the neutral bar. I checked in the meter base, and all the line side wires in the panel, and nothing is loose. Incoming voltage is correct. It seems to be concentrated to only one of the neutral bars (panel has two). About 6 circuits had discolored insulation and two of the six were severly burnt up. I've been to his house once before, he had a circuit not working and in the panel the neutral for that circuit was burnt at the end. I stripped the wire back and landed it back on the nuetral bar and it worked. Should we start systematically taking the devices out related to those affected circuits? Does anyone have any ideas as to what is causing this? I think it could be in a receptacle where the wires are stabbed into the back of the device. I cleaned up the panel this time, stripped all the bad insulation back, cut the wire ends and reterminated them, we have been watching for a change for about a month, none of the wires are showing a problem.:?
Neutrals burning up in panel
- Thread starter E.Hall
- Start date
- Status
- Location
- Lockport, IL
- Occupation
- Semi-Retired Electrical Engineer
If a neutral wire is overheating, and you don't see corresponding signs of overheating at any of the breakers, I would suspect that you have two or more circuits from the same phase that are sharing the neutrals. This would only manifest itself when the combined running load exceeds the ampacity of the neutral wire. For example, if circuits 1 and 3 share a neutral (not legal, but certainly possible), and in the actual running load at any one time is 15 amps on each of circuits 1 and 3, then the shared neutral wire would see a load of 30 amps. That would cause it to overheat, without any problem showing up on the phase wires. On the other hand, if the actual running load was only 8 amps on each of circuits 1 and 3, this could continue indefinitely without any signs of overheating. So I would call this not so much of a "ghost problem," but rather a "lurking problem." By that I specifically mean that the fact that you haven't observed any symptoms for a while does not prove that there is no longer a problem.
glene77is
Senior Member
- Location
- Memphis, TN
Are you saying that two hots off the same phase,
returning on the single neutral could heat ?
And we realize that two hots off different phases,
returning on the single neutral is OK.
- Location
- Tennessee NEC:2017
- Occupation
- Semi-Retired Electrician
Probably not what Charlie was saying in the red above, but if it was circuit 1 & 3 in the panel, they would be on different phases and could share a neutral.
- Location
- Lockport, IL
- Occupation
- Semi-Retired Electrical Engineer
It could overheat the neutral, because current flowing from the two breakers will add together to become the neutral current. You could have 20 amps flowing in each breaker, without either breaker tripping, and the neutral current would be 40 amps.
That is because when the two currents flowing from the two breakers add together to become the neutral current, they will be in opposition to each other. I mean that one current will be at (or near) its positive peak and the other current will be at (or near) its negative peak, so they tend to cancel each other out.
- Location
- Lockport, IL
- Occupation
- Semi-Retired Electrical Engineer
Since we are talking about a house, I infer that the panel is rated at 120/240 volt single phase. That would put circuits 1 and 3 on the same phase. That, at least, was the intent of my comment.
- Location
- Simi Valley, CA
I would agree with Charlie's thinking, including the parts about circuits 1 & 3 being on the same phase.
If split breakers (or thins, if you like) were installed, sometimes when the "installer" isn't thinking they go with the standard blk/red, blk/red instead of blk/blk, red/red.
If split breakers (or thins, if you like) were installed, sometimes when the "installer" isn't thinking they go with the standard blk/red, blk/red instead of blk/blk, red/red.
zbang
Senior Member
- Location
- Roughly 5346 miles from Earls Court
I've seen this a few times where someone, I assume, thought they were creating a MWBC with a single tandem breaker, often to a quad receptacle fed with 12/3 NM in the garage. Definitely unclear on the concept of MWBC.
jumper
Senior Member
- Location
- 3 Hr 2 Min from Winged Horses
Charlie's theory is correct, but 1 and 3 are not on the same buss/pole in most panels. Odd is left side and even is right.
1 and 3 are A and B.
- Location
- New Jersey
- Occupation
- Journeyman Electrician
I agree.
Cow
Senior Member
- Location
- Eastern Oregon
- Occupation
- Electrician
Just some ideas:
Improper MWBC's
Broken/cracked neutral bar
Bad connection between neutral bar and jumper from other side.
Improper MWBC's
Broken/cracked neutral bar
Bad connection between neutral bar and jumper from other side.
marti smith
Senior Member
It will be over a longer time period that you'll have to watch, but if you are unsure of the arrangement of conductors to phases, it is best to get with someone who understands it; have them go through the troubleshooting with you. It will be a really good learning experience. Otherwise, depending on the loads on the conductors compared to time, you will be cleaning up the neutrals all over again.
Last edited by a moderator:
- Location
- Lockport, IL
- Occupation
- Semi-Retired Electrical Engineer
Mea culpa. I see that now. I should have used circuits 1 and 5 as my example, or perhaps 1 and 2.
Takideezy
New member
- Location
- Williamsport PA
Measurement?
Measurement?
If over current is suspected why not measure with a clamp on ammeter?
Also, using a clamp on to measure the affected neutral... cycling breakers and identifying the hot to neutral relationship might be helpful. If the neutral current does not fall to zero - keep looking to determine if there is another breaker sharing the same neutral.
Good luck and Takideezy
Measurement?
If over current is suspected why not measure with a clamp on ammeter?
Also, using a clamp on to measure the affected neutral... cycling breakers and identifying the hot to neutral relationship might be helpful. If the neutral current does not fall to zero - keep looking to determine if there is another breaker sharing the same neutral.
Good luck and Takideezy
Charllie, when a panel is wired, it is done in such a way that the odd ckts are on the left and the even on the right. Ckts 1 and 3 would be on different phases (phase A and phase B respectively) , making it impossible for the neutral to have both phase currents on it at the same time, MWBC are legal.
- Location
- Simi Valley, CA
Most main panels, at least here on the west coast, are not side by side, so Charlie would be correct.
jumper
Senior Member
- Location
- 3 Hr 2 Min from Winged Horses
- Location
- Simi Valley, CA
Well, you can just keep your Zinsco panels on that side of the US.
Oh and we have a bunch of those in town. You could do a pretty good side business just selling breakers for those.:happyyes:
- Status