Why must Copper Bus Bar be Tin Plated?

• Thread 28003 "Silver Flashing vs Tin Plating of Switchgear Bus Bar"

A. Hi Keith. I am not by silence going to concede that you can do perfectly acceptable plating yourself following DIY instructions, but copper is not subject to the rapid corrosion which steel suffers from, so it's a good substrate to start with in any case :-)

I would use tin plating on electrical connections, and nickel plating on more decorative things and on moving contacts if any.

Luck & Regards,

A. Hi again, Harry. Here's a couple of thoughts about hobby plating ...

If it's something you want to do as a learning experience, that's fine. And people tend to be willing to be blind to small flaws in their own work whereas they'd demand to return it is purchased plating services turned out the same way :-)
But on the downside, you'll have iffy equipment, iffy chemistry, no instrumentation, no ability to analyze what's wrong, and no outside chemical analysis help. If you want to do it, the thing is, like in any other endeavor you have to practice ... and the way you practice is on scrap, not on any components that are precious.

You may able to find a shop to do small parts; the first question to ask them before getting lost in the detail is whether they do consumer parts. Many plating shops are set up with high volume production equipment and simply can't help you; some others may have been burned and won't work with consumers. It's akin to the wholesale-retail stuff you are familiar with: some plating shops are wholesale, some retail, and some whole-retail.

I am personally not familiar with people doing hot tin wiping on bus bar and electrical components, but people have been doing it on copper pots for many decades (copper is generally not a food-safe surface, so copper pots are 'tinned) ... and I'm not seeing any reason it wouldn't work. In fact, since it doesn't need to be food-safe you can use fluxes and solders that aren't food-safe and might make the task a bit easier. Please search the site for "tin wipe pots" or start with thread 25553, "Historical hand re-tinning of copper cooking utensils"

If you do try it, we'd certainly love to hear how it goes :-)

Luck & Regards,

A. Copper oxidizes and the oxides do not stay on the copper well. When they come off there is more copper exposed, which in turn oxidizes, and so-on. Also the oxides do not conduct well. This causes poor electrical contact, which then gets hot and increases the oxidation rate. The oxides, because of their poor conductivity, also cause arcing at the electrical contacts, eroding the copper.

A. Tin plating has two main technical advantages:

1. The thin tin oxide film (10-30 nm) forms on the surface of the tin coating could act as a shield, inhibiting further oxidation; and

2. Being a relatively soft metal, tin provides a low constriction resistance.

A. Tin plate works well to prevent corrosion and provide a good, clean contact surface. However, I prefer to heat the end of the copper end of the part to be coated, apply flux and then melt solder onto the surface, which I smooth out with a solder brush. Use lots of flux(soldering paste). The final step is to smooth our the coating and eliminate lumps and drips with a wet rag, wiping quickly to remove excess material.

Come to think of it, it might be easier to tin plate! Why didn't I think of that?

The advantage of soldering the connection surface is the heavy coating that results.

A. Hi Jagdish. The ampacity is not increased, but the reliability of the joint is increased.

Regards,

A. Hi.

Black discoloration of metals is often a sign of the presence of sulfides. But if you send a photo of the marks, people may be able to help you more.

Regards,

A. Hi, Sanj. May we assume you are referring to plating of bus bars? If you are talking about other kinds of contacts, this becomes an electrical engineering project to look at the voltages, currents, arcing, durability, contact pressure, required reliability, etc., etc.

For bus bar the standard would be to plate any aluminum completely with copper first, and then to plate the copper contact surfaces with tin. It is possible, however, to more directly plate aluminum with tin.

Regards,

A. Hi, Sanj. Current density will not be affected -- only the reliability of the joints.

Yes, entire manufacturing plants have been devoted to making aluminum bus bar and plating it with copper. Atotech used to offer, and may still offer, their Alstan process for plating aluminum directly with tin, skipping the copper plating step. So, both tin directly on aluminum and tin on copper on aluminum are common.

Certainly galvanic corrosion is possible any time any object is partially covered in one metal and partially covered with another metal, such as is the case with aluminum bus with copper, tinned or silvered ends -- but exposure conditions determine whether this is an actual problem or simply a potential concern, and often it's not.

Nickel plating tends to be hard, and it is used for contact surfaces such as battery chargers. Tin is significantly less expensive than silver, but the conductivity is lower and in some cases tin whiskers could be a problem.

Regards,

Hi Andy. I don't think an intermediate connection would make any difference, as the galvanic compatibility issue would still be there. If the environment is benign, galvanic corrosion will probably not be an issue. And if the area of tin (the baser metal) is large compared to the area of silver (the nobler metal), the issue would be minimized.

Regards,

A. Hi Jitender.

The design of electrical contact surfaces is an advanced electrical engineering science; so as a neophyte myself, I don't want to suggest that there is a simple universal answer to your question. But I do think that for 12 volt low amperage contacts, electroless nickel may be a good choice. It's what you'll usually see in AC adaptor devices for charging cell phones and cordless tools, and on the contacts of cordless phones, etc.

Regards,

A. Hi Monir. I must repeat that my knowledge of this science and technology is minimal, and that some engineers send their entire careers trying to deal with your question; there are surface transmission effects depending on frequency, burning and arcing issues, and hosts of others. But at low frequency, the current is carried by the copper, not the silver or nickel plating. They are there for hardness, wear resistance or lubricity, perhaps appearance, to prevent oxidation of the copper, etc.

Nickel is harder and more durable and is probably preferred for most repetitive contact applications; silver is probably preferred for permanent contact applications like bus bar joints and for easier soldering.

Regards,

A. Hi Ayanna. I can't see any reason for that to be a problem unless the environment is hostile.

Regards,

A. Hi Chris. To the extent of my own knowledge, I would not be concerned about this at all.

Regards,

A. Hi Deepak. In my estimation, the ends (contact areas) of aluminum busbar must always be plated. Here in the USA, aluminum house wiring used to be used until there was a fire at the Beverly Hills supper club in 1977, a tragedy that killed 165 people, and which was blamed on aluminum wiring. Please see
cmrris.com/news-real-estate-details/17/aluminum-wiring-hazard-mitigation.html
for a summary of what is thought to be wrong with aluminum wiring and how it may affect your decisions. Good luck.

Regards,