Receding insulation and oxidation

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Tainted

Tainted

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New York
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Engineer (PE)
A meter bank feeds apartments with multiple breakers. A circuit breaker tripped and they contacted me to investigate the issue, a lot of these apartments are fed by 2-pole 50A circuit breakers.

What could cause the receding insulation and oxidation forming in the wires? I'm suspecting that the receding insulation is due to overheating due to undersized wires and breakers with oxidation. Wires look burnt too. I'm not sure about the source for this oxidation either.
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That appears to be water damage and the corrosion has resulted a poor connection that creates excessive heat at the termination point.

It is unlikely that this is an overloaded circuit/undersized conductor issue.
 
don_resqcapt19 said:
That appears to be water damage and the corrosion has resulted a poor connection that creates excessive heat at the termination point.

It is unlikely that this is an overloaded circuit/undersized conductor issue.
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If they replace the wires, do they have to put some anti oxidant paste and that's it?
 
Besoeker3 said:
I don't think I have ever had to do that. I'm with don_resq and the water damage in this case.
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These wires are indoors. not sure where the source of water is coming from, it's not really humid in the room. Could even the tiniest volume of water effect it this bad?
 
I am doing a load letter on the apartment where the tripping happened and the breaker is undersized too.
 
What is the insulation type on those really bad looking ones? Do you have any other photos?
 
Tainted said:
Could not see any labels at all. Do you think the insulation might not be suitable for wet location?
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That doesn't matter as the breakers are not suitable for a wet location.

This got wet at some point in time. Is there any piping in the area? Does the supply cable for the panel originate outside the building?
 
It always looks that way when the terminals get loose. They overheat and then trip the breaker due to heat build-up. Just redo the terminations, keep the terminal screws as tight as possible and make sure you re-insulated the crumbling, burnt wire insulations, and be done with it. If you are not sure, take amp readings for good measure.
 
don_resqcapt19 said:
That doesn't matter as the breakers are not suitable for a wet location.

This got wet at some point in time. Is there any piping in the area? Does the supply cable for the panel originate outside the building?
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not sure, I don't think so.
topgone said:
It always looks that way when the terminals get loose. They overheat and then trip the breaker due to heat build-up. Just redo the terminations, keep the terminal screws as tight as possible and make sure you re-insulated the crumbling, burnt wire insulations, and be done with it. If you are not sure, take amp readings for good measure.
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When you say just redo terminations what do you actually mean? do you mean completely replace wires?
 
Tainted said:
If they replace the wires, do they have to put some anti oxidant paste and that's it?
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Looking at your picture, your wires are made up of copper (verdigris seen). You needed anti-oxidant paste when you are using aluminum wires to mate with copper lugs. There's no harm in listening to the old people here.
 
The termination 5th from photo left seems to have gotten hot (Screw blackened). Also the termination with the rag wire appears to have gotten hot based on discoloration of terminal.
If the conductors had gotten warm it will hasten oxidation under less humidity than it might otherwise.
Also the older copper "seems to" oxidize more readily than the newer copper. (Of coarse it could be simply the amount of time exposed).
The "burnt" breakers likely will need replacement. Also seen many times ageing breakers failing, either from tripping too easy or failing to trip at all.
 
This is my take. Likely someone just cut off the insulation more than they should have when the wires were installed. They didn't recede they just were always that way.

I don't know what's causing the copper to corrode. Could be just humidity especially if there it is a little bit of salt in the air. For instance it might be close to the ocean and over a very long time the humidity and salt in the air causes the copper to corrode.

Most times when circuit breakers trip it is because there is an overload. Loose wires occasionally can cause some extra heat which might cause a circuit breaker to trip at a lower current then it should. It's also possible that a circuit breaker could have failed in some way that causes it to trip at a lower amperage than it should.

I think your best bet is to do what one of the other posters suggested if it is possible. Cut off the wires at the point where the corrosion starts and reterminate them. Make sure when you reterminate them that you do not over tighten the screws.

Carefully inspect the circuit breakers for any sign of damage. If any of them are damaged replace them.

There is not much else you can do other than a gut and start over job with something like this.
 
petersonra said:
This is my take. Likely someone just cut off the insulation more than they should have when the wires were installed. They didn't recede they just were always that way.

I don't know what's causing the copper to corrode. Could be just humidity especially if there it is a little bit of salt in the air. For instance it might be close to the ocean and over a very long time the humidity and salt in the air causes the copper to corrode.

Most times when circuit breakers trip it is because there is an overload. Loose wires occasionally can cause some extra heat which might cause a circuit breaker to trip at a lower current then it should. It's also possible that a circuit breaker could have failed in some way that causes it to trip at a lower amperage than it should.

I think your best bet is to do what one of the other posters suggested if it is possible. Cut off the wires at the point where the corrosion starts and reterminate them. Make sure when you reterminate them that you do not over tighten the screws.

Carefully inspect the circuit breakers for any sign of damage. If any of them are damaged replace them.

There is not much else you can do other than a gut and start over job with something like this.
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I want to convince them to upgrade their entire meter bank and distribution (which they really should the building is so old). It is going to be hard to convince clients to pay for million dollar projects because they might think I'm a money grab but in reality I'm recommending what is right for them.. I agree there is nothing much they could do except to minimize hazards or gut everything and start over..
 
Tainted said:
I want to convince them to upgrade their entire meter bank and distribution (which they really should the building is so old). It is going to be hard to convince clients to pay for million dollar projects because they might think I'm a money grab but in reality I'm recommending what is right for them.. I agree there is nothing much they could do except to minimize hazards or gut everything and start over..
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It is hard to know what is "right" for someone else.

If the building is old enough that the electrical system needs redoing it probably needs a lot of other things like plumbing redone as well. I can't say I blame a building owner for not wanting to put a lot of money into a building electrical system that may well need to be torn down or seriously refurbished in the not too distant future.
 
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