[GreenKeys] Switch marked for aluminum wire.

[John Nagle]

CO/ALR is the "good" marking. OK for both copper and
aluminum wire.

Copper wire plays nicely with brass and steel terminals.

Aluminum wire has a problem. It has long, thin crystals.
The wire expands when heated and contracts when
cooled, as you'd expect. The crystals tend to align
perpendicular to the pressure on the wire, because they're
long and thin, like grains of rice.  So the wire gets a little thinner.
This breaks the solid connection between wire and terminal.
Then you get hot spots, and sometimes fires.
Big headache with 1960s-1970s aluminum house wiring.

See:

https://en.wikipedia.org/wiki/Aluminum_building_wiring#Coefficient_of_expansion_and_creep

				John Nagle