Aluminum... Even with everything done right, with approved hardware, aluminum wiring will tend to 'creep' (Aluminum mushing out of the way of the lug screw or clamp. Just recently I checked the main lugs on my 150A garage sub panel, and sure enough the neutral lug was loose. This was about 8 years after installation, with virtually no use (only one circuit used for lights until now.) However I believe this is only a problem with the softer grades of aluminum. If your enclosure were out of 7075, or 2024 my guess is you wouldn't see aluminum creep at all. 6061-T6 or similar would probably be OK also. It's the soft stuff that moves easily. They all form the oxide layer, so that's still a problem... In a pinch, I may be able to machine something, but shipping to there from here is probably expensive... Dan On 9/20/2017 8:28 AM, volt-nuts-request@febo.com wrote: > An aluminum electrical connection needs a few things to > be reliable: > > 1) a "springy" fastener > 2) mechanical precleaning > 3) an oxygen blocking coating. > > In the US, aluminum conductors are allowed for certain > usages. We used to allow 14 and 12AWG receptacle wiring, > but too many houses burned down. The receptacles were > redesigned for Cu or Al, but the codes remained stubbornly > against the practice. A few more times where copper prices > go through the roof, and the codes will change. > > For larger conductors, the wire, or bar, is brightened up > with Emory paper, or a stainless steel (important!) brush, > and then is covered with "Gorilla Snot", or some sort of > NoAlOx grease. NoAlOx is a grease made of an oxygen > resistant heavy oil, and a coarse emory grit. I like to > again rough things up after the NoAlOx is liberally applied. > > Finally, the conductors are tightened to specified torque > using a springy fastener... The springy fastener is often > simply an ordinary fastener with a "Bellview Washer" stack > to give it compliance. > > The big thing that makes high current aluminum joints > fail is thermal expansion. If the fastener isn't springy, > the aluminum expands from the heat, finds it cannot go > in the direction of the tightened fastener, and flows > elsewhere. When the joint cools, and the aluminum under > the fastener shrinks, the joint is now loose, and will > arc when current is once again applied, evaporating more > aluminum out of the joint. Soon the fire department will > be coming... if you are lucky. > > NoAlOx prevents this issue, if you use a springy fastener. > > -Chuck Harris

I guess I would have to ask, "How do you know everything was done 'right'?" The evidence you have stated makes a pretty good case that it wasn't. The neutral entering a sub panel at most has the same current going through it as one of the line input leads, though in a 240V sub panel, load balancing makes it typically much lower. If the neutral was installed correctly, and yet still cold flowed, then one or both of the line inputs should have cold flowed too. If they didn't, then I don't believe the neutral was installed correctly. The grades and finishes of the aluminum used in the electric supply systems are well specified and regulated through UL, and the NFPA. If the wrong grade, temperature, or alloy of aluminum was used; or the wrong service equipment, fastener, or torquing was used; or NoAlOx was omitted; then it wasn't done "right". As to aluminum oxide, unless it is removed, and prevented, a good electrical connection to the aluminum is impossible. NoAlOx does both. It prevents the oxygen from reaching the joint, and the grit embedded in it breaks through any oxide layer, and mechanically raises fresh aluminum to the surface to make a gas tight joint. Even though the manufacturer says it isn't necessary to mechanically remove the oxide layer, I do it anyway. I have never had an aluminum connection (made in this way) fail. -Chuck Harris Dan Kemppainen wrote: > Aluminum... > > Even with everything done right, with approved hardware, aluminum wiring will tend to > 'creep' (Aluminum mushing out of the way of the lug screw or clamp. > > Just recently I checked the main lugs on my 150A garage sub panel, and sure enough > the neutral lug was loose. This was about 8 years after installation, with virtually > no use (only one circuit used for lights until now.) > > However I believe this is only a problem with the softer grades of aluminum. If your > enclosure were out of 7075, or 2024 my guess is you wouldn't see aluminum creep at > all. 6061-T6 or similar would probably be OK also. It's the soft stuff that moves > easily. They all form the oxide layer, so that's still a problem... > > In a pinch, I may be able to machine something, but shipping to there from here is > probably expensive... > > Dan