what really happens?

[Ponchik]

Why does a connection between the aluminum and copper REALLY fail?

Is it copper to aluminum connection?
Is it because of bad connection to start with?
Is it the connector it self? Maybe it was or was not designed for aluminum.

Example install.

If I install a #10 copper to #8 aluminum using a large blue wire connector (Ideal wire nuts) and made sure the connection is nice and tight, will the connection ever fail because we have aluminum to copper connection?


Is the aluminum material used in older conductors different material than the newer conductors?

 

[cowboyjwc]

Copper and aluminum expand and contract at different rates. So what really happens is that he connection is always trying to loosen it's self.

 

[gar]

150629-1045 EDR

Aluminum oxidizes very quickly in air. Chemistry class. Aliminum oxide is a good insulator. Anodized aluminum has a thicker oxide layer than just the normal oxide layer of aluminum in air.

To use aluminum as a conductor the oxide layer must be broken down where it interfaces with another conducting material and prevented from redeveloping in that contact area.

.

 

[ggunn]

Copper and aluminum expand and contract at different rates. So what really happens is that he connection is always trying to loosen it's self.

That's not the problem it used to be back in the 1970's. Aluminum for conductors is now alloyed with other metals so that its coefficient of thermal expansion more closely matches that of copper.

 

[Ponchik]

Assuming the antioxidant is used, it is NOT the aluminum to copper connection that creates the problem. It is because of the natural heat generated by the current flow that expands the dissimilar material at different rates that creates the loose connection and eventually leads to the burned connection.

If the connection is tight then we should not have any issues??? Regardless if we use a regular wire nut or one that is rated for CU/AL.

 

[macmikeman]

Those of us who were working in the trade back in the seventies and even earlier for some probably experienced more problems with the mixed connections of copper to aluminum than what is encountered in modern wiring. Partly due to code changes prohibiting that practice and partly due to changing the alloy of the aluminum wire. I found more issues with aluminum wiring degrading at connection points due to no usage or improperly applied anti-oxidant grease, than incidents of degradation due to mixing of copper to aluminum. Exposure to salt damp air near the ocean was particularly hard on aluminum wiring back before they changed out the alloy.

 

[templdl]

I briefly reviewed the post but didn't pick up on what the terminations are. With beakers and I know if you use Cu conductor Al, Cu, or stainless steel terminals are allowed. With Al conductor Al or SS terminals are allowed.
As one of the other posters pointed out should a termination not be torqued per spec it will heat when loaded and cool when the load is redused whether CU or AL conductor. When the conductor heats and cools this esults is a further listening termination. As the load cycle continues the heating increases which escalates a terminal failure often resulting as arcing terminal. The arcing ionizes the air around it and scan involve an adjacent phase in addition to the metal mounting surface just below it.
I have seen the results of such a failure and it wasn't pretty.
Periodic thermal scans can be very helpful in helping to prevent such catastrophic failures.