burnt neutrals

[ciro mangione]

20 year old cutler residential load center, no arc faults, no shared neutrals, all seven neutrals terminated on left hand buss burnt insulation, no heat coming off buss, all terminations snug, highest current under 5 amps while under observation. we suspect there had been charger of an electric vehicle through a 120V garage outlet.
theories, educated guesses?
i have to figure out how to post a 4mb picture

 

[ciro mangione]

also no tripped breakers

 

[zbang]

Lightning strike? Those can do weird things.

 

[ciro mangione]

we do have lighting strikes occasionally but rarely here. there is another neutral buss in the load center with no symptoms at all. thanks for looking
i still have not figured out how to attach/upload images

 

[infinity]

You said that you had a problem with posting photos? They would certainly help.

 

[ciro mangione]

2 more pix to shrink

 

[ciro mangione]

You said that you had a problem with posting photos? They would certainly help.

i reduced the pix to 2mb each and was able to upload, thanks

 

[Little Bill]

i reduced the pix to 2mb each and was able to upload, thanks

The way the insulation looks, that's usually a sure sign of loose connections. You might check the connection to the other bar where the main neutral connects to see if it is tight.

 

[ciro mangione]

all neutral connections have been confirmed as tight, including the burnt ones.

 

[jim dungar]

The two screws above the large lug have heat discoloration, even though there are no conductors.
Tight screws may mean they are cross threaded/jammed. Have you disassembled and inspected?

 

[ciro mangione]

we removed and replace all the branch circuit neutral screws, none were cross-threaded. we did not touch the screws above the large lug.
i do see the discoloration you are referring to but cant understand how that would be meaningful.
also please notice the melted black plastic insulator at the bottom of the neutral buss in the first picture

 

[jim dungar]

we removed and replace all the branch circuit neutral screws, none were cross-threaded. we did not touch the screws above the large lug.

So, you do not know the quality of that neutral bar to the insulated cross bus connection.
IMO you should look at replacing that neutral bar and insulators, I believe they could be heat damaged.

 

[retirede]

Since the insulation damage is most severe nearest the neutral bus, the issue has to be poor (under torqued) connections. I suggest that someone re-tightened them before you got there.

If the issue was due to overcurrent, the insulation discoloration would be more uniform.

 

[ciro mangione]

i agree that i should replace the neutral bar and insulators, but that does not address why this happened.
i do not like to just change parts . i need to know the reason and the cause.

 

[ciro mangione]

Since the insulation damage is most severe nearest the neutral bus, the issues has to be poor (under torqued) connections. I suggest that someone re-tightened them before you got there.

i have pictures of this bus from 5 years ago and i am 99% certain that there has been no re-tighten prior to us.

 

[Fred B]

i agree that i should replace the neutral bar and insulators, but that does not address why this happened.
i do not like to just change parts . i need to know the reason and the cause.

I would be suspect of the main Neutral connections given all the neutral terminations on the bus in the picture had experienced some or significant melting. Add to that the melting of the bus isolator would seem to fit that the entire bus is heating at some point in time. It could even have been a utility neutral.
Are the neutral on opposite side and bus clean or show evidence of heating?

 

[Little Bill]

all neutral connections have been confirmed as tight, including the burnt ones.

I was saying to check where the left neutral bar connects to the right side to see if those connections were tight. Being that all the neutrals on that bar are effected, it very well could be a loose connection of the entire bar.

 

[ptonsparky]

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.

 

[Elect117]

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.

 

[ciro mangione]

I would be suspect of the main Neutral connections given all the neutral terminations on the bus in the picture had experienced some or significant melting. Add to that the melting of the bus isolator would seem to fit that the entire bus is heating at some point in time. It could even have been a utility neutral.
Are the neutral on opposite side and bus clean or show evidence of heating?

all of the neutral buss connections are firm. all of the right hand neutral buss terminations are in pristine conditions. there is no signs of overheating on the right hand side of the load center.
what do you mean by "It could even have been a utility neutral"?