Al/cu connections

[CraigDwyer]

Hello, we installed de-ox grease into wire nuts wherever al/cu wires are connected. After several months use the grease cannot be seen. I am wondering how to explain this to a client? I believe the components within the grease, coat the wires and moisture within the grease disapates, leaving just the chemical that prevents oxidation. Is this correct?

 

[Dennis Alwon]

I don't believe this is an approved means of termination aluminum/copper wire. Ideal makes a purple wirenut for that purpose.

 

[Dennis Alwon]

But then again they have their issues also

 

[GoldDigger]

Hello, we installed de-ox grease into wire nuts wherever al/cu wires are connected. After several months use the grease cannot be seen. I am wondering how to explain this to a client? I believe the components within the grease, coat the wires and moisture within the grease disapates, leaving just the chemical that prevents oxidation. Is this correct?

Do you coat the wires and then abrade the aluminum surface before putting it into the wire nut?
That is a necessary step even for compounds that claim to contain abrasives.
If you do not, you are depending on the wire nut to break through the insulating oxide layer. But even if you handle that properly, there are potential issues with the wire nut losing compression force on the wires after multiple thermal cycles. That is why specific wire nuts are tested and rated for Cu/Al connections. Extra design and testing requirements.

I you use a listed device, adding an anti-ox compound cannot hurt, and may be part of the instructions for use.

Once the metal parts are in good tight contact (called a gas-tight connection), the anti-ox has, in theory, done its job and is no longer needed. In practice, however....

 

[Dennis Alwon]

For years the Buchanan wirenuts- standard red ones- were listed for al/cu. We used them alot. To my knowledge they are still functioning however they did lose their listing.

 

[CraigDwyer]

Yes, we had stripped the wires of insulation about 3/4's of an inch and twisted the al & cu wires together tightly. De-ox was then squirted liberally into the nut and then tightly screwed back on. In most cases we used CoAlr wire nuts - purple. In some cases where the thermostat j box had 3-4 pairs of al cu pairs twisted together we simply squirted the de-ox into the wire nuts. The al wires were very stiff and several broke of at the j box and had to be re-stripped. Our concern was wires breaking deep in the box and causing us to pull new runs in. Therefore in some cases the de-ox was squirted into the existing wire nut, if they looked in good condition.

My question is what happens to the de-ox after the wires get warm/hot from current passing, does the moisture in the grease evaporate, leaving the chemical related to the de-ox coating the wires?

 

[GoldDigger]

Yes, we had stripped the wires of insulation about 3/4's of an inch and twisted the al & cu wires together tightly. De-ox was then squirted liberally into the nut and then tightly screwed back on.

My question is what happens to the de-ox after the wires get warm/hot from current passing, does the moisture in the grease evaporate, leaving the chemical related to the de-ox coating the wires?

I would expect that it might vary from one kind/brand of anti-ox to another. But there should be some form of liquid or gel coating left on the wire after use, IMHO.

When I say abrading the wire, I do not mean just stripping it. To remove the aluminum oxide layer you need to first coat the wire to keep the layer from re-forming immediately and then use sandpaper, file, or some other technique to break through that oxide layer before you twist the wires together. As a practical matter, no anti-ox can remove the oxide layer just by spreading it on. Your practice can cause all of the current to flow between the wires through the spring instead of directly from wire to wire. One possible result is what you see in the picture in Dennis' post.
Another may be that the connection gets hotter than it should and boils off the anti-ox.
Ideally if you make the connection properly, the resistance should stay low (at first anyway) if you take the wire nut off without separating the wires.

Read the linked pdf in post #12 in this thread for more authoritative information.

PS: There is a good chance that part or all of your problem with brittle wires is caused by nicking the wire when stripping it. That will provide a high stress point for a crack to start. However the spring wire inside the wire nut can cause a stress riser also.

 

[CraigDwyer]

Thank you very much for your response/s! They have been very helpful!