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"Preventing Copper From Discoloration Inside PVC Cable."

An ongoing discussion beginning back in 2000 ...


Q. Hi,

I have a cable plant, the problem I am facing is that in spite of using bright annealed copper the color turns black or green after the P.V.C coating within 20 to 25 days.Can you suggest any chemical that may be used during the copper drawing or annealing process which can protect the copper from oxidation inside the P.V.C and also does not effect the current carrying capacity.

Any person who can rectify this problem may please help.

Vaibhav Sondhi
cables - Delhi, India.

"Wire Technology"
from Abe Books


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A. Dear Vaibhav Sondhi,

Would you please tell me detailed process of P.V.C coating; does it need high temperature? If it does, how high?

I just want to know about the current discoloration-proof treatment that is used. You know BTA (benzotriazole) is always used for copper anti-discoloration, but sometimes it is not good enough to prevent discoloration for a longer time. I have been studying copper discoloration-proof for many years, and there are several kinds of anti-discoloration products, please tell us your present problem as detailed as possible.


Ruifeng Bai
- P.R.China


A. Please add copper passivator to solve this problem.

- Tirunelveli, Tamilnadu, South India

February 9, 2009

Q. Mr. Bai,
Can you please explain in details about discoloration phenomenon during & after insulation of copper conductors.

Anil Kapoor
copper cables - India

July 20, 2016

Q. Hello!

I am facing the similar problem of getting copper black while coating PVC. Have you people already discussing the same problem get any solution so far? If anyone knows please help me I will be grateful.


Iqra Ayoub
- Lahore, Pakistan

Hi Anil; hi Igra. The black is certainly an oxide or sulfide; sulfur certainly turns copper black, as has been reported thousands of times in the Chinese wallboard scandal. If there is a way to limit exposure to sulfur and high temperatures, that probably would help. Ruifeng probably can't condense his "many years of study of this subject" into a paragraph of two that covers all situations and which will turn us all into experts able to deal with a general issue that he has spent years on, so ...

As he requested of Vaibhav, please tell us the details of your own particular situation. What are you presently putting on the copper as corrosion inhibitor, benzotriazole? Any other tarnish inhibitor, like a chromate? Does this happen on every meter of cable, or only occasionally. How big is the cable? What temperature is the PVC. What does the installation look like -- is it a continuous wire drawing and PVC coating line? I am fairly confident that someone with years of experience can be helpful to us towards solving a carefully detailed highly specific problem, even though unable to educate us into being experts ourselves. Thanks, and get back to us with details please!


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