burnt neutrals

ptonsparky said:
My thoughts are the 4th wire up from the bottom began the heating damage. Most likely from improper torque. The rest were collateral damage. Overtightened damages the conductor and creates overheated connections as well as under.
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i agree that the middle neutral wire shows the most damage and was perhaps ground zero. but to reiterate all terminations have been confirmed as good.
 
Elect117 said:
A couple of things I would check as well:

1) The white phase conductor on the two pole breaker isn't tied to any neutral at a load or something.
2) The neutral bar itself isn't loose. There appears to be discoloration on the top of the bar. The connection between the neutral bus to the bar might be loose. Also make sure it isn't bonded to the case (unless it should be).
3) The bare grounds aren't touching the neutral bar. There can be small arcs between the neutral and grounds if they are close or lightly touching creating heat.
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1) the white conductor is not used. the install ran a 12/3 rather than a 12/2
2) as previously reported all connections have been verified as tight/firm. the neutral is floating. no main breaker in load center.
3) good point, when we first opened the panel there was a slight chance that a ground wire was touching the neutral, but no continuity proved otherwise.
 
ciro mangione said:
1) the white conductor is not used. the install ran a 12/3 rather than a 12/2
2) as previously reported all connections have been verified as tight/firm. the neutral is floating. no main breaker in load center.
3) good point, when we first opened the panel there was a slight chance that a ground wire was touching the neutral, but no continuity proved otherwise.
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I have also seen where the bending space / larger wire presses up against the plastic that holds the neutral offset from the enclosure and breaks the plastic. We didn't know if it was broken when installed or if it happened from being pressed against over time.
 
Elect117 said:
I have also seen where the bending space / larger wire presses up against the plastic that holds the neutral offset from the enclosure and breaks the plastic. We didn't know if it was broken when installed or if it happened from being pressed against over time.
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the standoff does not appear to be broken only melted.
 
I would test the voltage drop of that neutral bar with my tester set to 20 Amps.
 
I cannot tell from the photos. Are all the wires fully inserted in the buss, or could one or more only be partly in contact with the screw?
 
Looks to me like a bad strap connection from one neutral bar to the other.
All of the left bar connections are overheated, including the screws at the top where there are no conductors other than the connecting strap to the opposite side bar.

the wires furthest away from the strap connection are burned the worst, as they have the most voltage drop.
The bad strap connection could be on either side of the panel, not just on the side experiencing the overheating.
 
MTW said:
Looks to me like a bad strap connection from one neutral bar to the other.
All of the left bar connections are overheated, including the screws at the top where there are no conductors other than the connecting strap to the opposite side bar.

the wires furthest away from the strap connection are burned the worst, as they have the most voltage drop.
The bad strap connection could be on either side of the panel, not just on the side experiencing the overheating.
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both sides of the horizontal neutral strap have been verified as good.
i am considering paralleling the strap with #6 conductor.
actually the middle of the neutrals is the worst
 
ciro mangione said:
both sides of the horizontal neutral strap have been verified as good.
i am considering paralleling the strap with #6 conductor.
actually the middle of the neutrals is the worst
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How did you verify their good? did you do a fall of potential test while under load, or a visual inspection?
 
The early post made mention to possibility of a 120V EV charger being used in the garage. Is one of those burnt wires belonging to the garage circuit?

The picture looks to be a subpanel, has the N/G bonding been lifted?
Are all the EGC are on the one side that have the burnt wires?
Have you confirmed that each neutral only serves just the one circuit? Have seen where a junction box was made up with multiple circuits run through that someone tied all the neutrals together. Seen as many as 4 circuits brough together is such a way. If one of the circuits was to loose its neutral path to the panel the other neutral would simply pick up it's load and the Home owner would never notice and issue because of the splice everything would continue to work. But if the combined loads being shared under the remaining neutral was to exceed the rating of the wire it would heat up maybe even burn. it would never trip the breaker as the breaker is only seeing the loads of the "hot side" not of the neutrals.
I would expect to see heating evidence on most of the length not just at the termination, but wouldn't rule it out if other things have been checked.

Most likely is loose connections. You state that all the connections are tight. Not to be insulting but how was this confirmed? Did you just try to see if they would tighten anymore? Use a torque wrench or driver to verify mfg specs? Did you actually back them off? With this much burn I wouldn't be surprised if the screws are seized and seem to be tight, and wire actually welded in so seem to be tight. (seen it) These wires need to be removed and stripped back to clean insulation and re-terminated anyway. That bus is compromised at best now, and I would think the inspector could ask that it be replaced with that much damage.

Been seeing issues with the mfg. of the bus screw or bar so that they seem tight before you even start, hitting the torque spec without even getting the wire slightly held. One was hitting the 20inlb (Eaton BR specs) without even turning the screw at all or wire even under the screw. Also, been having to run them in and out multiple times before you can get them to torque. Been a bigger issue more recently.
 
The first time I used my new Klein Torque screw driver was on a CH neutral bar. 25-30 years ago? . The #12s were basically cut thru. I demonstrated it to my area State EI. Somewhere along the way the bars were changed so that was no longer an issue,

I agree that the quality of product has dropped considerably in the last few years since manufacturing of load centers have been moved out of country. I've moved connections to a different setscrew because the first wouldn't thread in to begin with.
 
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