Tin Plating on Connectors

[Dodgee]

Does anyone know of a study comparing tin plating of connectors such as hylugs to just straight aluminium? In addition would the etching on top of a tin plated connector (removing part of the tin plating) have any long term effects on that lug?

 

[busbar]

In the simple sense, this typically constitutes modification of the connector, voiding any NRTL-listing [like UL 486B] and promoting decreased corrosion resistance of its aluminum-alloy body.

 

[jbartos]

Suggestion: It just depends on a situation. The tip plated aluminum appears to be an improvement to the aluminum itself. Visit

http://www.gwelec.com/images/ca3-02pdf/p3,8,9.pdf

for:
Bi-metallic crimp type or migweld bimetallic
connector with silver plated
copper top and tin plated aluminum
bottom.
Any associated label, e.g. UL label may be applicable and required as hinted in the above posting.
Additional details pertaining to the original posting would help.

 

[Dodgee]

First off thanks for the replies. As for more details.

We are considering etching civic addresses, onto the tops of tin plated aluminium lugs found in residental 120/240V transformers (outdoor transformers). The etching would be done on one lug, of the three which go from the transformer to the home.

The concern is after a number of years (10-15-20) will the etching off of part of the tin, cause connectivity problems. Perhaps if etching becomes standard, then tin plating might not be required?

 

[IRstuff]

If you have that much control over the process, why not etch before the tin plating? TTFN

 

[Dodgee]

Etching is done in the field, when they know the exact address to be etched.

 

[busbar]

Why not ask T&B, Penn-Union and Burndy directly?

 

[peebee]

Keep in mind I have no idea what I'm talking about here. That said. . . .

Aluminum won't corrode like steel, it forms a self-protecting layer of aluminum oxide (essentially sapphire) over itself almost immediately on exposure to air. As soon as that layer forms, oxidation almost completely stops. The sapphire is highly resistive, makes for bad connections, and is the cause for concern when using aluminum.

My guess is that if you keep your etching away from any contact areas, you should be OK. Etch anything in a contact area, and you're asking for problems.

I strongly agree with busbar and would check with the manufacturers. Be aware that you could potentially void the UL listing of your lugs, that is perhaps your biggest concern.

 

[kenvlach]

I would think that electrical types should know what galvanic corrosion is. [At least, busbar seems to.] If you etch all of the way through the tin plating to the aluminum, any moisture will set up a galvanic couple between the two dissimilar metals. Any dust will make it worse. In this case, the aluminum being more anodic, it will preferentially corrode at the Al/Sn interface. The aluminum hydroxide corrosion product will eventually cause the tin plate to lift and peel or flake off.

peebee, your comments about aluminum forming a protective layer are only true if you have both a ~pure Al alloy (as EC grade) that is kept clean and away from any other metal.
Also, sapphire (a 'doped' crystalline alumina) only forms at very high temperatures, the low temperature oxide film is amorphous (glassy structure). You are correct about it causing conductivity problems.

Dodgee, Try using a polyurethane paint for labelling if there is sunlight (UV) exposure.

 

[peebee]

I know enough about galvanic action to know that the rate of corrosion is highly dependant on the surface area of the interface. The Al/Sn interface at the area of etching is incredibly small. These things get scratched by wrenches all the time, they work just fine.

In addition, dodgee's most likely using copper conductors, and these are most likely Al/Cu rated lugs. The copper will cause the tin to sacrifice anyway. I'm sure they accounted for this in the design of the lugs.

I'm not saying that I recommend removing tin from the lugs, or using uncoated Al lugs. But all in all, engraving an address in the back of the lug away from the contact area should have little or no effect on the life or reliability of the lug. I'd still recommend checking with the vendors and/or UL soley due to the litigious nature of our society.

 

[peebee]

Also, kenvlach, regarding your statement regarding aluminum forming a protective layer only being true if you have both a ~pure Al alloy (as EC grade) that is kept clean and away from any other metal:

Damn near every outdoor chain-link fence I've ever seen is made from aluminum. The few steel exceptions are immediately obvious due to the red crusty oxide that forms on them. The reason for the extensive use of Al is the very low corrosion rate in air: 20-year old Al fences look remarkably similar to 1-year old fences. There's nothing particularly exotic about fence aluminum, and they are commonly bonded to steel, copper, concrete, dirt, etc., with no significant change in their rate of corrosion.

 

[kenvlach]

peebee,
I was concerned about corrosion over a 10+ years in what seems to be an exposed environment. I use both Sn-plated-Al & Cu lugs in a much more severe environment (anodizing & plating shop) for cathode & anode bar connections, fill the end of the cable w. EJC before lugging, coat the exterior with EJC, cover w. plastic film & then tape.
Haven't plated Sn onto Al, but Ni plated-Al fails the salt spray test if there is any porosity or scratches in the coating. The white Al hydroxide spreads underneath the plating.

Please check those aluminum chain-link fences with a magnet, maybe they're just better quality galvanized (with possibly a clear chemfilm). This is a good application for suitable aluminum alloys; I think it's uncommon due to cost.

I don't want a debate; just wanted to support earlier concerns re corrosion & why UL might not approve of the etching from the viewpoint of a metallurgist with lots of Al experience.

 

[Dodgee]

I just wanted to thank you for the help. You've brought up some great points. Just for some clarity.

- You're right, the environment is very exposed to the elements. Dust and water will settle into the etched area.
- The lug is Al with Sn plating (etching done on the top of the lug).
- Lug is about 3 inches in length.
- The lug is connected to a Cu busbar (side on the lug used to connect the lug to the bar)
- 120V phase to ground on the lug.
- fretting will also be an issue.

Thanks again.

 

[peebee]

"fretting will also be an issue."

Don't fret too much about it

 

[Milenko]

The most serious problem in tin-plated contacts is the occurrence of fretting or fretting corrosion resulting from samll ooscillatory movement of the contacting interface. The motion can be generated by vibration, thermal expansion of the dissimilar metals in contact, by switching on and off etc. It is very difficult to eliminate deleterious effects of fretting, but lubrication can only reduce these effects. The manifestation of effects of fretting is dramatic increase in contact resitance leading to arcing, melting and even evaporation of tin. For further inquiries ask milenko37@sympatico.ca

 

[rtrimblepe]

Is this too simple-minded or could you attach some sort of identification onto the cable similar to what is used in substations when marking control wires?

If not, perhaps a tie-wrap and some paper in a laminated covering?

http://machinerunner.com/Laminating/Pouch-Laminators/Pouch-Laminators-49.html

Just a thought although not very high tech. Seems easier than etching onto the connector.

 

[Dodgee]

rtrinblepe,

Tags are the current way of doing this. The problem is that, with time, they fall off and disappear. People have even pulled them off from inside the TXs, which are locked. It seems a good way, for the long term, is etching. While tags are okay, they far from great. Etching would be perferred as long as it doesn't overly effect the connection.