TopBand: Sources of radial wire

[Larry Higgins]

><There is another reason to avoid aluminum.  It's the reason electricians
>are not fond of it.  That is, when aluminum is in a compression connection
>such as a screw terminal and it cools, the aluminum is squeezed.  The
>squeezing causes it to spread sideways.  When it warms up, it doesn't
>expand as much as it was squeezed because it's now wider.  Sort of like
>expecting toothpaste to be resilient.  The result is that the copper
>terminal expands more than the aluminum, so the joint becomes loose.  If
>any appreciable current is flowing through the joint, it will then become
>hot.  If hot enough, the aluminum will begin to oxidize.  Aluminum oxide is
>a pretty good insulator.  You get the picture.  I'm using aluminum wire for
>my elevated radials, but I make sure that I periodically check the screws
>in the connections for tightness.  There are also joint compounds available
>from electrical suppliers which will help. >
>
>
>Actually what happens is that electrolysis will occur when you join two
>dissimilar metals, e.g. copper and aluminum.  The connection will begin to
>corrode  when exposed to the weather and  will become very high resistance if
>it even conducts current at all.  This will happen despite the different
>coefficients of expansion between the copper and the aluminum.  There is a
way
>to retard the electrolysis, though.  If you use an antioxidant compound (such
>as Penetrox or Cramolin) you can slow the process down significantly.  I
think
>this is the joint compounds you refered to Larry.
>
>73................de Goose W8AV 


Goose, you're right about the electrolysis.  Actually, both effects occur:
the unequal compression/expansion (whether indoors or out) coupled with low
resilience,  and electrolysis.  And yes, those are two of the compounds
mentioned.  There are other brand names as well.  They do help a lot.  Some
of them are sold as aluminum/copper joint compounds, but they also work
well with aluminum/aluminum joints.  

If you are using an aluminum plate and attaching aluminum wires, you can
still get electrolysis and/or compression problems, unless you are also
using aluminum screws, washers, and nuts.  So it's a good idea to dope
everything with joint compound.

73

Larry, N9DX
  


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