Duplex Outlets - Fire hazard - TVI

David C. Hallam dhallam at RAPIDSYS.COM
Fri May 22 10:02:54 EDT 2009

Having worked in the electrical wire and cable industry from about 1960 
to 2000, I know a fair amount about the aluminum house wiring situation.

The cost to conductivity ratio favored Al over Cu.  However an 
unexpected problem soon developed.  The cause was "creep" or cold flow. 
  When pressure is applied to a point contact, a material tends to flow 
away relieving the pressure. Unfortunately Al has a high tendency to 
cold flow.  The problem really came to light when Al wire was used with 
back wired switches and outlets.  Since the contact area in a back wired 
receptacle is small, it relies on high pressure to make the connection. 
  This caused the Al to creep away from the point of high pressure.  As 
the creep proceeded, the contact resistance increase causing heating 
which increased the rate of creep, a degenerative situation.  The result 
was fires.

After the problem became apparent, the wire manufactures developed Al 
alloys that greatly reduced or eliminated the creep problem, usually 
with the addition of a very small amount of iron to the Al and some 
residual cold work, but there were others.  However, the damage had been 
done and no one wanted Al wiring.

The fix for houses with Al wiring was to add Cu pigtails at each 
receptacle.  The pigtails were attached to the Al wire with a wire nut 
and a small amount of anti corrosion compound.

Cu Clad Al bombed as far as house wiring goes.  It solved the creep 
problem, but its cost was prohibitive.  The cladding process ate up part 
of the favorable cost to conductivity ratio.  The real killer was the 
value of the manufacturing scrap.  Cu and Al have a high scrap value 
because they can be easily recycled.  Cu Clad Al has very little value.


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