# Burnt wiring conductivity.



## electrictim510 (Sep 9, 2008)

I often come across wiring that had burned, like most of us after a connection has failed. I always cut back the burnt part of the wiring to get a good copper connection to the wiring but I have a more technical question about the burn itself. 

A formal apprenticeship probably would of taught me this but if someone can point me toward some reading on this subject I would appreciate it:

When a wire overheats to the point where it burns does the conductivity of the wire itself change? Kind of an off the wall question since we don't keep the burnt wire but I just want to know more about it.


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## MDShunk (Jan 7, 2007)

Proably ought to go to google and type this in the search bar:

copper oxide site:www.copper.org


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## electrictim510 (Sep 9, 2008)

I don't mean the burnt surface, I mean the wire itself, the core.


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## MDShunk (Jan 7, 2007)

electrictim510 said:


> I don't mean the burnt surface, I mean the wire itself, the core.


I don't think you know what you're talking about. :laughing: How do you "burn" the core of copper wire?

Silly boy. :thumbsup:


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## electrictim510 (Sep 9, 2008)

Let me clarify: When we encounter a burn, say one that has been over time and has heated to the point that it has hardened and 'burned' the surface; if the copper oxide from the burned is cleaned off does the copper wire still keep its electrical potential?


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## MDShunk (Jan 7, 2007)

electrictim510 said:


> Let me clarify: When we encounter a burn, say one that has been over time and has heated to the point that it has hardened and 'burned' the surface; if the copper oxide from the burned is cleaned off does the copper wire still keep its electrical potential?


Yes. Copper is still copper. It didn't change into something else.


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## electrictim510 (Sep 9, 2008)

MDShunk said:


> Yes. Copper is still copper. It didn't change into something else.


Ok, I just thought since it overheated it may of changed the properties of the wire itself. Thanks for the response.


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## mikeh32 (Feb 16, 2009)

changing reply...

be back later


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## Robertd0824 (Nov 5, 2019)

Burned wires looses conductivity and easily heats up


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## HackWork (Oct 2, 2009)

Robertd0824 said:


> Burned wires looses conductivity and easily heats up


I don't know which part of your post I love the most. The part where it is filled with information to support your claim. The part where it bumps an 8 year old thread. Or the part where you show a picture of your backside. I hate to see you go, but I love to watch you leave :brows:


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## Signal1 (Feb 10, 2016)

HackWork said:


> I don't know which part of your post I love the most. The part where it is filled with information to support your claim. The part where it bumps an 8 year old thread. Or the part where you show a picture of your backside. I hate to see you go, but I love to watch you leave :brows:


You mean, don't go away mad, just go away?


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## jw0445 (Oct 9, 2009)

There's dust on this one


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## samgregger (Jan 23, 2013)

Copper is an element. unless it heats up to it's melting point, it's still going to be the same diameter and have the same ampacitiy when it cools down.


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## Forge Boyz (Nov 7, 2014)

samgregger said:


> Copper is an element. unless it heats up to it's melting point, it's still going to be the same diameter and have the same ampacitiy when it cools down.


I'm curious about this. I thought that if copper was burnished and hardened from overheating it would lose conductivity and cause problems if reterminated on new terminals. I cut the hard wire away to prevent more problems.

Sent from my SM-G970U1 using Tapatalk


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## jw0445 (Oct 9, 2009)

Forge Boyz said:


> I'm curious about this. I thought that if copper was burnished and hardened from overheating it would lose conductivity and cause problems if reterminated on new terminals. I cut the hard wire away to prevent more problems.
> 
> Sent from my SM-G970U1 using Tapatalk


You did good. The hard wire tends to break more easily while twisting on a nut.


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## MikeFL (Apr 16, 2016)

In Physics you learn that a shiny metal surface is a better conductor.

Polish the bottom of your cooking pans and you'll cook better.

Current wants to flow on the circumference of a wire. 

If I had to testify in court, I'd say a tarnished (oxidized) wire is going to be less conductive than a shiny new conductor. By how much? Well you'd have to set up the test and find out. 

Generally speaking, in building wire, once the insulation is compromised by fire (heat), it has to be replaced before inspector is going to allow power to be reconnected, so it's not so much the wire that gets the attention, but the insulation.


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## MTW (Aug 28, 2013)

I have often wondered this myself. I think we all understand that the copper hasn't magically become another metal, but I wonder the same thing - is the copper now less conductive because of the extreme heat? I play it safe and cut off the damaged wire and never re-terminate the discolored copper, but something that is really hard to do with an outlet that has burned up and several inches of wire in the box is destroyed.


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## splatz (May 23, 2015)

This is the kind of thing I have learned my high school grasp on chemistry is ok for idle speculation not enough to base an important decision. 

This is from https://www.elandcables.com/the-cable-lab/faqs/faq-what-are-annealed-conductors



> *FAQ: What are annealed conductors?*
> 
> When metal is cold worked or formed it becomes work hardened or strain hardened. Copper conductors go through a considerable amount of work hardening as the copper rod is drawn down through ever decreasing die sizes until the required conductor dimension is achieved. Copper in this state is known as hard drawn copper.
> 
> ...



So maybe (maybe) if copper is heated up due to overload then cools, it's annealed, and becomes softer. Annealed is more conductive, but if it is softer, it may not be elastic enough to keep good tension in terminations. Hard metals are highly elastic, just with forces much greater than necessary to deform things with usually think of as elastic, like rubber. But a soft metal is not so elastic. So maybe it doesn't make good contact, which would make better contact in a screw terminal, play dough or rubber? 

But I don't know. Just spitballing. I'd call the manufacturer, who would probably cover their ass, commit to nothing, and tell you when in doubt, rip it out. Doesn't cost them anything so why would they try harder. If I could find some engineering reference that said it's OK, then I'd say it's OK. But I would not base it on my halfassed metallurgy.


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## MikeFL (Apr 16, 2016)

And in annealing it's not just the time & temp of the heat, but the rate at which it's cooled which determines the physical properties. 

IIRC it's fast cooling for greater hardness (as in drop in a vessel of water).


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## dmxtothemax (Jun 15, 2010)

If a copper wire has heated up to the point that a connecttion has failed ?
Then it sure is "possible" that the cables conductivety has changed.
How ever ? How significant is the change ?
A check with a good quality meter will soon tell the story.
I would guess that the vast majority of times damage is minmal.
And therefore running a new cable may not be needed.


:glasses:


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## gpop (May 14, 2018)

MikeFL said:


> And in annealing it's not just the time & temp of the heat, but the rate at which it's cooled which determines the physical properties.
> 
> IIRC it's fast cooling for greater hardness (as in drop in a vessel of water).


fast cooling copper (quenching) make the material softer (more malleable). 
The atoms line up into a neat pattern when hot then when quenched the atoms get locked in to that pattern. Over a period of time the atoms move loosing the pattern which results in copper becoming stiff. 
If you do plumbing with copper pipe its fairly standard to heat a old piece then quench it so you can bend it. (old stuff is hard to bend and may crack)


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## argile_tile (Aug 12, 2021)

MDShunk said:


> Proably ought to go to google and type this in the search bar:
> 
> copper oxide site:www.copper.org


the "moderator" is my pet pieve on any website. they usually IP BAN people with correct infomation while favoring false information - SPREAD IN USA.

so. moderator. why don't you have a talk with me?

COPPER CORE BURNING: There are history channel episodes / segments on the topic. It is the bane of Electric companies, studies exist to prevent it while reducing the weight of copper needed to avoid it.

As far as "rusting from the inside out", I'd like your argument on how oxygen gets in the center of the wire before the outer part of the wire. Also about whether work hardening changes "the color" of metal without oxidation.

nuclear physics


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## argile_tile (Aug 12, 2021)

gpop said:


> fast cooling copper (quenching) make the material softer (more malleable).
> The atoms line up into a neat pattern when hot then when quenched the atoms get locked in to that pattern. Over a period of time the atoms move loosing the pattern which results in copper becoming stiff.
> If you do plumbing with copper pipe its fairly standard to heat a old piece then quench it so you can bend it. (old stuff is hard to bend and may crack)


that's good information. it's called WORK HARDENING. however - i see no URL or science to suggest that work hardening (moving copper) and copper core burning are ... firmly related


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## argile_tile (Aug 12, 2021)

Physics for Scientists and Engineers, 3rd edition, SERWAY

Ch. 43 Molecules and Solids, p. 1268

Fermi Distribution (the free electron theory for metals)

All atoms have "valence", 1s, 2s, 2p, 3s, 3p, ... Between those there are "gaps" and they are far from all the same pull as to different elements. When the gap is just perfect _and_ an electrical voltage is applied: the electron can move freely. (the "conduction band"). There are two main forces pulling different directions: atomic strong bond pulling in nucleons together, any like-charge electrical repulsions pushing them all apart, "banding" / valence shells they "agree" on, sometime an un-grounded/un-shielded inner atom imbalances exposed, and of course anothing exterior (applied voltage or radiation).

High voltage moves the atoms to destroy this balance. The "nearest neighbor", the compaction of the copper atoms together, makes the conduction band poor. Exactly more information of how, why, when, how to calculate is data I was just trying to find myself.

We can't say "work hardened" because "overhead lines are hard copper, home copper bendable soft copper: both conduct very well". But it's the right line of thinking about the problem.

Could it be rust oxidation reactions? The problem is copper core burning happens from the inside out (the browning). So no, it's safe to call that moderator comment as: trolling.


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## gpop (May 14, 2018)

so stranded copper when heated between 200-900 C in a oxygen atmosphere doesn't become coated in copper oxide which is a mott insulator. The insulator on the cores doesn't affect a crimp as only the outside strands are in contact with the lug and hardened copper still crimps at the same pressure even if its harder to deform. 

Well that's interesting i guess

Doesn't cost me nothing to cut the burnt end off before re-terminating the wire so i guess i will carry on doing it the wrong way.


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## p.harold.2065 (4 mo ago)

So does copper wiring that has been pinched and presumably heated up (discoloration) lose its conductive ability?


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## backstay (Feb 3, 2011)

Let sleeping dogs lie.


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## paulengr (Oct 8, 2017)

gpop said:


> so stranded copper when heated between 200-900 C in a oxygen atmosphere doesn't become coated in copper oxide which is a mott insulator. The insulator on the cores doesn't affect a crimp as only the outside strands are in contact with the lug and hardened copper still crimps at the same pressure even if its harder to deform.
> 
> Well that's interesting i guess
> 
> Doesn't cost me nothing to cut the burnt end off before re-terminating the wire so i guess i will carry on doing it the wrong way.


It’s a semiconductor. Not a good one but it’s a semiconductor,









An Overview of Copper(I) Oxide Semiconductors


Copper (I) oxide or cuprous oxide is an inorganic compound having the formula Cu2O. It is a principal oxide of copper. It is a red-colored solid, which is a component of certain antifouling paints. The compound may be red or yellow based on the particle size.




www.azom.com





It was used long before first SiC then later Ge and then Si and now back to SiC. Now CuI is being re-examined:



https://onlinelibrary.wiley.com/doi/full/10.1002/pssb.201248128


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## paulengr (Oct 8, 2017)

p.harold.2065 said:


> So does copper wiring that has been pinched and presumably heated up (discoloration) lose its conductive ability?


Two different effects and yes it is affected.

Copper is highly conductive. You won’t notice a change in conductivity except with a micro ohm meter. The inductance also changes quite dramatically. This affects the AC impedance and even DC resistance but it’s a subtle change.

What is not so subtle is something we call constriction resistance. If you pinch and neck down a narrow section of conductor at normal conditions it just gets hotter faster than the surrounding copper. But during a surge because of magnetic effects electrons simply can’t flow through the narrow gap making the mordants nonlinear…it current limits and gets even hotter.

Inside current limiting fuses we intentionally do this to control the fuse properties (current limiting, melting point).









How Current Limiting Electrical Power Fuses Work - Industrial Fuse, Hardware, Equipment Distributor


Power fuses are like overdraft protection on checking accounts., and in this case, power equipment is the bank. Power overloads are like bouncing a check, and fuses respond to overdraws accordingly, protecting the system and keeping it balanced. In the illustration below, you can see how a...



blog.monsterfuses.com


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## readydave8 (Sep 20, 2009)

paulengr said:


> If you pinch and neck down a narrow section of conductor at normal conditions it just gets hotter faster than the surrounding copper.
> 
> 
> 
> ...


and that's why it's bad to close a door with extension cord running through it


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## SWDweller (Dec 9, 2020)

No offense, why is this even being asked? I would NEVER do a job and leave burnt wiring. I can not imagine that many on this board would allow it.
In fact have turned down work because the owner wanted to . Not with my license. Same with a lot of used materials. 

WIth out test of conductivy with machines and certifications I do not have nor do I want the question is mute.


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## p.harold.2065 (4 mo ago)

paulengr said:


> Two different effects and yes it is affected.
> 
> Copper is highly conductive. You won’t notice a change in conductivity except with a micro ohm meter. The inductance also changes quite dramatically. This affects the AC impedance and even DC resistance but it’s a subtle change.
> 
> ...


Thank you for your response


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## p.harold.2065 (4 mo ago)

SWDweller said:


> No offense, why is this even being asked? I would NEVER do a job and leave burnt wiring. I can not imagine that many on this board would allow it.
> In fact have turned down work because the owner wanted to . Not with my license. Same with a lot of used materials.
> 
> WIth out test of conductivy with machines and certifications I do not have nor do I want the question is mute.


I agree. This question has nothing to do with LEAVING burnt wiring though. I just came across a section of wiring that had been pinched, so I stripped it to see if it was cut because it wasn't passing current and noticed it was still intact and wondered could it stop current flow if it was burnt. Just being a nerd, looking to learn more about things life presents to me. That's why the question was asked. And now I know so thank you.


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## paulengr (Oct 8, 2017)

p.harold.2065 said:


> I agree. This question has nothing to do with LEAVING burnt wiring though. I just came across a section of wiring that had been pinched, so I stripped it to see if it was cut because it wasn't passing current and noticed it was still intact and wondered could it stop current flow if it was burnt. Just being a nerd, looking to learn more about things life presents to me. That's why the question was asked. And now I know so thank you.


You are getting close to the idea of a hidden failure.

Say the trip mechanism in a circuit breaker fails. It manually trips and closes and seems fine. The only way that you know it failed us if something faults and it doesn’t trip or you test it and it doesn’t trip, or trips early or late. This is called a hidden failure. In maintenance and reliability we look at whether or not it is worth it (for downtime, financial, or safety reasons) to do routine tests to detect hidden failures or just run to failure.

Wiring is the same way. Failure rates are quite low though, and most problems like overcurrent trip the breaker/fuse/overload relay.


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