Letter 28003

Silver Flashing vs Tin Plating of Switchgear Bus Bar [Texas] 

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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.

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 Whatley
Manufacturer - Beaumont, TX, USA

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 v/s 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 Vahanwala Automaxx   Bangalore, Karnataka, India

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 Whatley
Swithgear - Beaumont, TX, United States

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 spec may work for you!

Khozema Vahanwala Automaxx  Bangalore, Karnataka, India

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 typicaly up to 1800mm long and 200mm wide copper busbars, any help would be appreciated

Shaun Moore
- Kent, UK

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

Khozema Vahanwala Automaxx  Bangalore, Karnataka, India

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

Sujoy Roy
Electrical Engineer - Philadelphia, PA, USA

We are manufacturing of switchgear in saudi arbia could you please advise us about the minumum thikniss of the silver and tin plating of the busbar as per the international standard.
Thanks.
Engr.Hussam Al-Sakka
Production Manager
Switchgear Business Unit (SBU)

Hussam Al-Sakka
- Dammam, Saudi Arabia

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