[volt-nuts] Best way to measure micro Ohms

[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