It's still widely used here in Washington State. Not for most of the branch
circuits, but for the service entry and large loads like the kitchen stove.
The problem was galvanic corrosion when aluminum wire was used with
terminals made of a dissimilar metal or joined with wire nuts to copper
wire. This created resistance which would heat up. When it's used today, it
needs to be used with hardware designed for aluminum, and should be coated
with special grease.
Have you checked the stove and dryer circuits? Our house (near Vancouver
BC), we have multi-strand aluminum for the electric stove and the
original electric dryer circuit, while all other circuits are copper.
I asked the house inspector about it when we were in the process of
buying, and he said that the multi-strand aluminum for large appliances
was not a problem, while solid aluminum branch circuits would be flagged
(and might trigger an increase in insurance premium).
The house I just sold (not in SD, but the opposite corner of the
country) had multi-strand aluminum wire for the dryer and stove
circuits. The house was built in '86. I'm pretty sure it's still
in use for these applications.
It wasn't just galvanic corrosion. Aluminum expands more than copper or
brass when it warms up and is very malleable. So as it tries to expand
under the screw/terminal, it actually deforms itself and changes shape to
flattish oval that extrudes out from around the terminal. Then when the
aluminum cools it shrinks down and is no longer tightly held by the
screw/terminal. This of course creates a loose connection so the next time
the circuit is loaded it gets hotter than before, more
expansion/deformation, looser connection, more heating etc... etc... etc...
FIRE! FIRE! FIRE!
Learning all this, the industry started making equipment with
connections/terminals that would remain tight with aluminum wire. The
standard now is that such devices must be marked Al-Cu if suitable for
Aluminum or copper wiring. If it doesn't say that, do not use it with
Aluminum is commonly used for services and may be used for higher amp
circuits. Both are reliable as far as I know.
The problems in the US were with 15 and 20A branch circuits. The problem
was great enough UL delisted everything (early 1970s) and came up with
Devices like switches and receptacles (15/20A) for use with aluminum are
marked CO/ALR. The aluminum alloy was also changed to reduce expansion.
CO/ALR receptacles are not tested with old technology wire (which is
most of the 15/20A wire installed).
In addition to the expansion problems with old wire, aluminum is very
reactive and very rapidly forms a thin insulating oxide layer on the
surface. It is standard practice to use an antioxide paste. The surface
may also be abraded to remove the oxide (particularly recommended on
15/20A circuits). Larger terminals deform the aluminum which breaks
through the oxide. The screws on 20A receptacles aren't as likely to
break through. Wirenuts can also fail because of oxide.
Yes. You need to reduce the gauge number by 2, which increases the
cross-section area by a factor of about 1.6, for the aluminum wire to
have the same resistance per unit length as the copper wire.
So if a particular circuit requires 12 AWG copper, it will require 10
AWG aluminum. That's a rule of thumb based on the physics of the two
metals and the way the gauge scale is set up (where the cross section
almost exactly doubles for every decrease of 3 in the gauge number).
Regulatory requirements may differ.
My house was built in '72 and has aluminum wiring in the branch circuits.
When I purchased it, I went through and pigtailed the aluminum wire to
copper wire and then ran copper wire to the switch/receptacle. I put anti
oxidation paste on each of the connections.
Note: I also check the connections once a year to make sure they are still
tight. It is also worth noting that after 25 years of neglect I found only
one connection where there was evidence of heat being generated i.e. burned
Don't use AL wire--especially for branch circuits. AL is generally
good for temp wiring because it is light and cheaper than copper.
Even though legal in FL, I never used SER for service entrances;
copper only. Save yourself a future headache.
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