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-requ...@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
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