Homebrew PCBs

In a message dated 5/19/2004 2:53:33 PM Central Standard Time, 
les@lnewell.screaming.net writes:
Does anyone know why aluminum is bad for house wiring?  (real question,  not 
a joke)  Is it that aluminum has a greater thermal expansion ratio than 
copper, and so the connections worked themselves apart?<<
This may CONTRIBUTE to the problem, but the MAIN reason is that aluminum 
oxidizes INSTANTLY upon contact with oxygen in the air, and then stops oxidizing 
as soon as an invisibly-thin layer of alum.oxide is created (same "chemical" as 
saphires or rubies!).   Same stuff that is used to make much sandpaper.  And 
that AlO³ is a "perfect" insulator.  So, with that working caused by the 
condition in your question, any of that which may have been scraped away and 
"contact made" upon initial installation is instantly replaced, as soon as oxygen 
touches the bare Al surface, again.  This resistance causes heat which FURTHER 
exascerbates the problem, and on it goes until the heat so generated becomes 
hot enough to melt plastic and start fires.  Now, the "heavy stuff" from the 
utility may still be aluminum, but that is fastened to the "bus" in the initial 
main breaker-panel with specially-treated connectors which (mostly-) impede 
this oxide-generation.  Thus, $Dollars are saved by using a few short feet of fat 
Al wire where copper was used decades ago.  It boggles MY tiny mind that the 
people who "thought-up the use of Al wire in house-wiring" didn't realize what 
they were DOING!  The $ speaks loudest, I guess!
                            Jan Rowland


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