Originally Posted By: Greg Fretwell
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We had an interesting topic today at the IAEI meeting. A couple people from the wire industry came by and told us some stuff about aluminum wire.
The “problem” wire is alloy 1350 that was originally designed for overhead spans. It was not designed to bend very much and tight bends will quickly fracture it. It also was not designed with use in pressure terminals and the coefficient of expansion is a problem.
I guess we all know that.
The new AA 8xxx alloys are designed to be bent and also have a coefficient of expansion that in more compatible with copper/brass
CO/ALr devices use different materials in the screw itself that is more compatible with aluminum.
In NRTL testing they determined that aluminum conductors are actually better in the typical aluminum alloy lugs than copper!
(Hundreds of tests, 4 failures, 3 copper)
The test rapidly cycled between 90c and 0c under load
There was no significant difference in testing whether they used the antioxidant or not. Proper torque was a lot bigger factor.
80% of lugs tested in installed equipment were OVER torqued and that is as bad as under torque. In some cases the overtorque had actually damaged the conductor to the point that it might cause a failure.
Once properly torqued you should never re-torque.
The CU/AL rating of a terminal has more to do with expansion rate than galvanic action. That is probably why aluminum outperformed copper in an aluminum alloy lug.