Discolored Copper

[Cookie]

Does anyone know what causes this? Is the wire safe to use? Does it have the same conductivity and anneal as "regular" copper? For that matter does this occur with UK rolls of twin and earth?

https://www.reddit.com/r/electricians/comments/lm5nb2

 

[radiohead]

The ground wire has been tinned so it has a silver colouration, the insulated cores have not. In a used cable discolouration (darkening) of the copper is a sign of overheating, but if this is a new and approved cable it is just a characteristic and I would not be concerned.

 

[littlespark]

Did you hit your thumb with a hammer?

 

[Lucien Nunes]

It looks strange even for tinned wire, too golden and dark, unless the picture has some weird colorimetry. I have a lot of tinned wire around here, new, old and truly ancient, and it's pretty consistent in appearance and does not look like that.

I would not like to guess at what the colour signifies, and would want to go back to the manufacturer and check with them. It would be interesting to do a resistance check of the EGC against the other cores, which would more or less confirm whether it is a surface effect or throughout the cross-section.

I've never seen it in UK twin & earth. although I have seen slight tarnishing of the copper surface in a few low quality cables. Historically all our wiring cables were tinned and looked silvery. Alongside our change from imperial sizes to metric around 1970, we started using plain copper. Tinning had been necessary with vulcanised rubber insulation to avoid reaction with the sulphur, but was a needless expense in most applications of PVC-insulated cables.

 

[Cookie]

The ground wire has been tinned so it has a silver colouration, the insulated cores have not. In a used cable discolouration (darkening) of the copper is a sign of overheating, but if this is a new and approved cable it is just a characteristic and I would not be concerned.

Earth wires are tinned in modern romex cable. I've seen brown, reddish, bronze and even silver colored copper in romex on occasion.

 

[Cookie]

It looks strange even for tinned wire, too golden and dark, unless the picture has some weird colorimetry. I have a lot of tinned wire around here, new, old and truly ancient, and it's pretty consistent in appearance and does not look like that.

I would not like to guess at what the colour signifies, and would want to go back to the manufacturer and check with them. It would be interesting to do a resistance check of the EGC against the other cores, which would more or less confirm whether it is a surface effect or throughout the cross-section.

I've never seen it in UK twin & earth. although I have seen slight tarnishing of the copper surface in a few low quality cables. Historically all our wiring cables were tinned and looked silvery. Alongside our change from imperial sizes to metric around 1970, we started using plain copper. Tinning had been necessary with vulcanised rubber insulation to avoid reaction with the sulphur, but was a needless expense in most applications of PVC-insulated cables.

Not seen in the UK? I suspect you guys have better quality control. Or perhaps your copper tends to be more pure. I'm clueless to be honest, but at the same time I can't help but think your copper is held to higher standards in some way or another.

 

[Lucien Nunes]

Copper purity has a very strong influence on conductivity. I can't say with certainty but I would expect any copper that is so impure as to be visibly the wrong colour, would be rejected for low conductivity. Therefore discolouration of an otherwise usable cable I would expect to be a surface effect only. Of all European cables of good manufacture, surface discolouration of plain copper through chemical exposure is probably most seen in the popular EPR / Polychloroprene heavy-duty outdoor cables H07RN-F series.

I'm not sure whether chemical exposure is a likely cause of the discolouration in that NM sample, because the differing substances contacting the surface (insulation, filler, sheath) would probably create a patchy or striped effect. I am more inclined to think it was discoloured before the cable was made up.

It's unlikely that our QC is any better than yours. Our accredited certification body specifically for cables (BASEC) puts its stamp on most major manufacturers' products, and electricians are exhorted to use BASEC-approved cables. But there is no obligation to have BASEC approval to sell or use a cable. Historically we had the CMA (Cable Manufacturers' Association) and cables manufactured by CMA member companies were badged either 'Association Grade', or 'Non-Association Grade' which did not have to meet the same specs for IR, insulation thickness etc.

These days much of our cable is imported, Turkey is a large supplier (not sure if Brexit changes this.) We had a recall a few years ago of cables from a Turkish manufacturer, sold through one of the big DIY store chains, that had undersize conductors which is a pretty blatant fault that really should not have reached the retail shelves.

 

[Cookie]

Copper purity has a very strong influence on conductivity. I can't say with certainty but I would expect any copper that is so impure as to be visibly the wrong colour, would be rejected for low conductivity. Therefore discolouration of an otherwise usable cable I would expect to be a surface effect only. Of all European cables of good manufacture, surface discolouration of plain copper through chemical exposure is probably most seen in the popular EPR / Polychloroprene heavy-duty outdoor cables H07RN-F series.

I'm not sure whether chemical exposure is a likely cause of the discolouration in that NM sample, because the differing substances contacting the surface (insulation, filler, sheath) would probably create a patchy or striped effect. I am more inclined to think it was discoloured before the cable was made up.

It's unlikely that our QC is any better than yours. Our accredited certification body specifically for cables (BASEC) puts its stamp on most major manufacturers' products, and electricians are exhorted to use BASEC-approved cables. But there is no obligation to have BASEC approval to sell or use a cable. Historically we had the CMA (Cable Manufacturers' Association) and cables manufactured by CMA member companies were badged either 'Association Grade', or 'Non-Association Grade' which did not have to meet the same specs for IR, insulation thickness etc.

These days much of our cable is imported, Turkey is a large supplier (not sure if Brexit changes this.) We had a recall a few years ago of cables from a Turkish manufacturer, sold through one of the big DIY store chains, that had undersize conductors which is a pretty blatant fault that really should not have reached the retail shelves.

Hopefully that is whats causing it. I'm also thinking it may have something to do with the annealing process, or that the copper was overheated. But its just a wild guess.

FWIW I bought a 2100 watt UK hair dryer with 0.75mm2 flex. When I ran the dryer the cord didn't even seem to get warm. Where as some 120 volt cords despite being larger in become get warm.

 

[Lucien Nunes]

It won't be the conductivity of the copper making the difference, or at least if it is, the cable is unapproved counterfeit garbage.

 

[telectrix]

Where as some 120 volt cords despite being larger in become get warm.

could that be because the voltage is halved, so the current is doubled?

 

[pc1966]

Where as some 120 volt cords despite being larger in become get warm.

could that be because the voltage is halved, so the current is doubled?

And I2R losses 4 times more?

 

[pc1966]

@Cookie do you have some of the cable to play with?

I wonder what it looks like if filed/cut, as my initial reaction was it looked suspiciously like coated aluminium.

 

[Cookie]

Where as some 120 volt cords despite being larger in become get warm.

could that be because the voltage is halved, so the current is doubled?

Right, but the AWG (mm2) is adjusted to take that into account.

 

[Cookie]

@Cookie do you have some of the cable to play with?

I wonder what it looks like if filed/cut, as my initial reaction was it looked suspiciously like coated aluminium.

Sadly nothing, however I've personally encountered this before (red color) and it was indeed copper all the way through.

For some reason now and then US rolls of NM end up with odd color copper on one of the conductors.

 

[telectrix]

Sadly nothing, however I've personally encountered this before (red color) and it was indeed copper all the way through.

For some reason now and then US rolls of NM end up with odd color copper on one of the conductors.

maybe that's the infuence of the red indian native american population? ??