Duplex Outlets - Fire hazard - TVI

[David C. Hallam]

Scott,

I don't want to get into a discussion of the fine points of why Al house 
wiring failed in the market.  However, I was a metallurgical engineer 
involved, one among many, in developing a solution to the house fire 
problem.  Certain alloys were developed, Southwire's EEE and Super T 
among others, that had higher cold flow resistance.

Admittedly receptacles were developed with large contact head screws and 
a specified torque to break through the surface oxide layer and provide 
a greater contact area.

The basic problem was still one of cold flow.

David
KC2JD/4

Scott Johnson wrote:
> I have to respectfully disagree with the cold flow analysis.  Aluminum is a
> very active metal that almost instantaneously forms a surface oxide, which
> passivates the surface. (this is what give aluminum is corrosion
> resistance). The oxide is also an insulator, so as it oxidizes, the contact
> resistance goes up.  If one uses a large surface pressure contact (such as a
> wire around a screw), the exposure to atmosphere is reduced, and the
> corrosion is minimized, and all is well.  The back wire contact is a point
> contact, very small contact area, and frankly, I would use it even for
> copper wire.  That is why spec. grade outlets are not back wired!  The
> phenomenon of cold flowing applies to tightly bundled PTFE wiring, but I
> don't think it applies to aluminum in this case.
> 
> Scott V. Johnson W7SVJ
> 5111 E. Sharon Dr.
> Scottsdale, AZ 85254
> (602) 953-5779
> Cell (480) 682-7219
> scottjohnson1 at cox.net
> 
> 

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