[A/S] Aluminum wire

[bilmoran@xxxxxxx]

The following was posted as a quote by a resident electrical engineer 
describing the problem associated with aluminum wire. I agree and would like 
to add an additional factor not mentioned, OXIDATION. 
When the aluminum expands and is forced to change it's shape (because the 
screw restricts the expansion, which is called extrusion) it exposes material 
that
was not exposed to the air before. Aluminum when exposed to air oxidizes
which appears as a white powder. This oxidation offers electrical
resistance in the circuit and also occupies physical space. The next time
the cycle occurs, the oxidation occupies space and causes the aluminum to
extrude further resulting in more exposed aluminum, oxidation etc. The
amount of resistance caused by the oxidation between the screw and the 
aluminum wire causes heating in the connection resulting in failure 
(heating/fire).
This is why using the paste to exclude the oxygen from reaching the aluminum 
is critical. Also to have screw and wire that expand at the same rate. (Cu/Al 
devices)

"I've considered that the looseness of single strand aluminum wires 
comes from the differential expansion between the wire and the brass 
screw. As the wire heats, aluminum expands more than brass but since 
the brass screw retains it the aluminum has to spread at right angles 
to the screw pressure. Then when the assembly cools the aluminum 
shrinks in all directions and the screw is loose. Next time there's a 
load it heats a lot faster and repeats the deformation. All together 
a bad idea, "bad scene", fires and shocks including deaths result 
when the ground wire looses its connection. Been there, done that as 
an expert witness. Had to explain deaths to parents.

Gerald J... "