Re: [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
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Re: [volt-nuts] Best way to measure micro Ohms

[Mitch Van Ochten]

I once repaired a Valhalla 2555A Current Calibrator 
  (good for up 
to 100A output). It uses aluminum bus bars inside to route the current.  The 
junctions between the bars had become higher than normal impedance and it could 
no longer deliver 100A.  I disassembled all joints, cleaned them with emery 
cloth, then applied a drop of Caig Deoxit and re-assembled.  That was over four 
years ago and no complaints from the customer so far.


Best regards,

mitch

-Original Message-
From: volt-nuts [mailto:volt-nuts-boun...@febo.com] On Behalf Of Andre
Sent: Wednesday, September 20, 2017 3:54 AM
To: Discussion of precise voltage measurement
Subject: Re: [volt-nuts] Best way to measure micro Ohms

Hi, just my $0.02 worth.
I have some instrumentation amplifiers here also looked into low resistance 
connections for my other projects.

If I recall correctly you need to look at the electrochemical series. For 
interconnects on Al you want a metal similar on the ES.
The oxide is a problem but if you connect it properly eg with an oil droplet 
and clamp connnector using compatible vernier it should be fine.

Looking at how wiring in the US is done might give you some ideas.

Kind regards, -Andre

From: volt-nuts  on behalf of Charles Steinmetz 

Sent: 19 September 2017 21:30
To: Discussion of precise voltage measurement
Subject: Re: [volt-nuts] Best way to measure micro Ohms

David wrote:

> A practical problem is the tools available to me. The U-channel was 
> machined by someone in my radio club, and the rest I made myself using 
> nothing more than a drill and hand tools. It would be nice to make 
> more out of one piece, but it would require better tools than I have 
> readily available. There are certainly engineering companies that 
> could do a better job, but it would be quite costly.

If you can make a decent drawing of what you need (it doesn't have to be a 
draughtsmanlike job, as long as the form and measurements are clearly shown), I 
bet you can find someone in your radio club, or a personal friend, or someone 
on a list you frequent to make it for a nominal cost (you would probably need 
to pay for the raw material, although I don't charge for anything that comes 
out of my scrap pile and this is true of many other home shop machinists).  
HSMs are behind every third or fourth garage door in the UK.

Another option would be to build up the parts as you have done, then have 
someone TIG weld the pieces together.

Best regards,

Charles


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Re: [volt-nuts] Best way to measure micro Ohms

[Andre]

Hi, just my $0.02 worth.
I have some instrumentation amplifiers here also looked into low resistance 
connections for my other projects.

If I recall correctly you need to look at the electrochemical series. For 
interconnects on Al you want a metal similar on the ES.
The oxide is a problem but if you connect it properly eg with an oil droplet 
and clamp connnector using compatible vernier it should be fine.

Looking at how wiring in the US is done might give you some ideas.

Kind regards, -Andre

From: volt-nuts  on behalf of Charles Steinmetz 

Sent: 19 September 2017 21:30
To: Discussion of precise voltage measurement
Subject: Re: [volt-nuts] Best way to measure micro Ohms

David wrote:

> A practical problem is the tools available to me. The U-channel was
> machined by someone in my radio club, and the rest I made myself using
> nothing more than a drill and hand tools. It would be nice to make more out
> of one piece, but it would require better tools than I have readily
> available. There are certainly engineering companies that could do a better
> job, but it would be quite costly.

If you can make a decent drawing of what you need (it doesn't have to be
a draughtsmanlike job, as long as the form and measurements are clearly
shown), I bet you can find someone in your radio club, or a personal
friend, or someone on a list you frequent to make it for a nominal cost
(you would probably need to pay for the raw material, although I don't
charge for anything that comes out of my scrap pile and this is true of
many other home shop machinists).  HSMs are behind every third or fourth
garage door in the UK.

Another option would be to build up the parts as you have done, then
have someone TIG weld the pieces together.

Best regards,

Charles


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