[volt-nuts] Best way to measure micro Ohms

[Dan Kemppainen]

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 at 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