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Silver Flashing vs Tin Plating of Switchgear Bus Bar

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Q. I am the Quality Assurance Manager for a manufacturing company in Southeast Texas. We manufacture switchgear and various other products for marine and industrial use. Our switchgear ranges from 600VAC to 15KVAC, and from 0 to 6000 Amps. At one time we primarily used tin plated copper bus bars; however, with industry changes we have since moved to silver flashed copper bus bars.

Recently we shipped some switchgear from the US to Singapore, and when the customer uncrated the switchgear, s/he found silver flashed copper bus that appears to have begun oxidizing/corroding. We are unsure of the cause at this time; however, we have shipped many products overseas with no reported incidents.

silver plated copper bus bars

My question(s) are as follows:

1. Is silver flashing better/worse than tin plating? Why?
2. Which one, if either begins to tarnish/oxidize sooner, given the same weather conditions?
3. What is the recommended thickness of both?

I would like the answers to get a better understanding as to why copper bars are plated/flashed, is silver better than tin, why is that, the similarities/differences, and to prevent this situation from repeating.

Steve Wdeleted
swithgear - Beaumont, Texas


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A. Dear Mr. Steve,

The coating of Silver in this case appears to have been too thin, I presume its Copper that we are seeing below the busbar. Whatever the Silver thickness, you must use an anti-tarnish over Silver. The minimum should be 3 to 6 microns.

The prediction about Silver vs. tin corrosion resistance is like this: You can probably afford to put on 10 microns of tin for every micron of Silver at the same cost. 10 microns of Tin will outdo 1 micron of Silver hands down. Fixed Busbars like yours are traditionally only Tin plated + anti tarnished; only moving parts that are likely to arc are generally silver plated.

khozema Khozema Vahanwala
Saify Ind
 
Bangalore, Karnataka, India


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Q. It appears we are going to move back to using tin plated copper bus bars for our switchgear. The next question is what is the "standard" or recommended plating/flashing thickness of tin? What is it for silver?

Steve W [returning]
swithgear - Beaumont, Texas, United States


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A. I have plated busbars to a spec of 5 - 12 microns of Tin. You have to determine your plating thickness requirement based upon "Fitness of use" for your current / corrosion requirements. I do not believe that anyone else's spec may work for you!

khozema vahanwala Khozema Vahanwala
Saify Ind 
Bangalore, Karnataka, India


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Q. We are also tin plating switchgear busbars. We use an 8 micron finish of acid tin, we also send parts to hot climates with no reports of corrosion. One problem we do have is a milky finish on our busbars. analysis shows no faults with the solution. I cannot understand why we get this "milky" result so often, the busbars are typically up to 1800 mm long and 200 mm wide copper busbars, any help would be appreciated

Shaun Moore
- Kent, UK


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A. Have you ensured that your Tin plating bath was always under 27 °C? You may have lost some of your stannous.

khozema vahanwala Khozema Vahanwala
Saify Ind 
Bangalore, Karnataka, India


+++++++appended

Q. Please let me know what shall be the thickness of tin coating used in copper bus?

Sujoy Roy
Electrical Engineer - Philadelphia, Pennsylvania, USA


February 17, 2008appended

Q. We are manufacturing switchgear in Saudi Arabia. Could you please advise us about the minimum thicknesss of the silver and tin plating of the busbar as per the international standard?
Thanks.

Engr. Hussam Al-Sakka
production mgr., switchgear - Dammam, Saudi Arabia

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Ed. note: Sujoy, Hussam. We appended your questions to a thread where they are already answered. Get back to us if you have additional questions.



October 11, 2010

Q. Which is the best, silver or tin plated?

Jim Raub
Switchgear engineer - crosby, Texas USA


December 28, 2012

A. Hi Jim. Please see Khozema Vahanwala's first response -- I found it very informative.

Regards,

pic of Ted Mooney Teds signature
Ted Mooney, P.E. RET
finishing.com
Brick, New Jersey


April 11, 2013

A. I'm not in the plating business, but rather in the electrical design and installation side of the industry.
What I have noticed is that in a high H2S (Hydrogen sulfide) environment copper and silver have a high oxidation rate in a short period of time.

I have had generators fail because the silver solder holding the winding retaining bars oxidized completely away allowing the windings to flex under load and short.

This was a gas plant with 200,000 PPM H2S in the inlet stream.

Tin is not affected.

Just sharing.

Tony Romero
- Katy, Texas USA



December 28, 2012

Q. Dear receiver

We are switch board assembling company and we have a difficulty with bus bar corrosion and discoloration.
We have no idea about the necessary chemicals to avoid above.
With regard to tin plating on bus bars, I want to know the chemical to be applied or any other method to use to do this.

A.Pathmasiri
electromech engineering - Maharagama, Sri Lanka



A. Hi. The chemical to be applied is tin electroplating solution, but it's not a chemical that is wiped on or brushed on like a paint; rather, it's a manufacturing process where the bus bar is alkaline cleaned by immersion, rinsed, acid activated by immersion, rinsed, electroplated by application of DC electricity while the parts are immersed in a solution of stannous sulfate or potassium stannate (for example -- there are other choices) with proprietary addition agents, rinsed, and immersed in a bath of tarnish inhibitor.

The normal way this is done is by sending the parts to a plating jobshop. That is not to say that you absolutely can't do it in-house; but that requires a knowledge base, a significant capital investment, and probably operating and waste generation permits. Good luck.

Regards,

pic of Ted Mooney Teds signature
Ted Mooney, P.E. RET
finishing.com
Brick, New Jersey

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